Document:

<PAGE>   1

                                                                    EXHIBIT 4.19

                               GUARANTEE AGREEMENT

                         DATED AS OF _________ __, 20__

                                 BY AND BETWEEN

                                  U.S. BANCORP,
                                  AS GUARANTOR

                                       AND

                            WILMINGTON TRUST COMPANY,
                                   AS TRUSTEE
<PAGE>   2
                             CROSS REFERENCE TABLE(1)

<TABLE>
<CAPTION>
SECTION OF TRUST                                                      SECTION OF
INDENTURE ACT OF                                                      GUARANTEE
1939, AS AMENDED                                                      AGREEMENT

<S>                                                                  <C>
310(a)....................................................................4.1(a)
310(b)...............................................................2.8; 4.1(c)
310(c)..............................................................Inapplicable
311(a)....................................................................2.2(b)
311(b)....................................................................2.2(b)
311(c)..............................................................Inapplicable
312(a)...............................................................2.2(a); 2.9
312(b)...............................................................2.2(b); 2.9
312(c).......................................................................2.9
313(a).......................................................................2.3
313(b).......................................................................2.3
313(c).......................................................................2.3
313(d).......................................................................2.3
314(a).......................................................................2.4
314(b)..............................................................Inapplicable
314(c).......................................................................2.5
314(d)..............................................................Inapplicable
314(e).......................................................................2.5
314(f)..............................................................Inapplicable
315(a)..............................................................1(d); 3.2(a)
315(b)....................................................................2.7(a)
315(c)....................................................................3.1(c)
315(d)....................................................................3.1(d)
316(a)...............................................................2.6; 5.4(a)
316(b)...................................................................... 5.3
316(c)..............................................................Inapplicable
317(a)......................................................................2.10
317(b)..............................................................Inapplicable
318(a)....................................................................2.1(b)
</TABLE>

(1)      This Cross-Reference Table does not constitute part of the Agreement
         and shall not have any bearing upon the interpretation of any of its
         terms or provisions.

                                      -i-
<PAGE>   3
                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                                               PAGE

<S>      <C>                         <C>                                                                       <C>
ARTICLE 1 INTERPRETATION AND DEFINITIONS..........................................................................1

         SECTION 1.1.               Interpretation and Definitions................................................1

ARTICLE 2 TRUST INDENTURE ACT.....................................................................................5

         SECTION 2.1.               Trust Indenture Act; Application..............................................5

         SECTION 2.2.               Lists of Holders of Securities................................................5

         SECTION 2.3.               Reports by Guarantee Trustee..................................................5

         SECTION 2.4.               Periodic Reports to Guarantee Trustee.........................................5

         SECTION 2.5.               Evidence of Compliance with Conditions Precedent..............................5

         SECTION 2.6.               Guarantee Event of Default; Waiver............................................6

         SECTION 2.7.               Guarantee Event of Default; Notice............................................6

         SECTION 2.8.               Conflicting Interests.........................................................6

         SECTION 2.9.               Disclosure of Information.....................................................6

         SECTION 2.10.              Guarantee Trustee May File Proofs of Claim....................................6

ARTICLE 3 POWERS, DUTIES AND RIGHTS OF GUARANTEE TRUSTEE..........................................................7

         SECTION 3.1.               Powers and Duties of Guarantee Trustee........................................7

         SECTION 3.2.               Certain Rights of Guarantee Trustee...........................................8

ARTICLE 4 GUARANTEE TRUSTEE......................................................................................10

         SECTION 4.1.               Guarantee Trustee; Eligibility...............................................10

         SECTION 4.2.               Appointment, Removal and Resignation of Guarantee Trustee....................11

ARTICLE 5 GUARANTEE .............................................................................................12

         SECTION 5.1.               Guarantee....................................................................12

         SECTION 5.2.               Waiver of Notice and Demand..................................................12

         SECTION 5.3.               Obligations Not Affected.....................................................12
</TABLE>

                                      -ii-
<PAGE>   4
<TABLE>

<S>      <C>                        <C>                                                                          <C>
         SECTION 5.4.               Rights of Holders............................................................13

         SECTION 5.5.               Guarantee of Payment.........................................................14

         SECTION 5.6.               Subrogation..................................................................14

         SECTION 5.7.               Independent Obligations......................................................14

ARTICLE 6 LIMITATION OF TRANSACTIONS; SUBORDINATION..............................................................14

         SECTION 6.1.               Limitation of Transactions...................................................14

         SECTION 6.2.               Ranking......................................................................15

         SECTION 6.3.               Subordination of Common Securities...........................................15

ARTICLE 7 TERMINATION ...........................................................................................15

         SECTION 7.1.               Termination..................................................................15

ARTICLE 8 INDEMNIFICATION .......................................................................................15

         SECTION 8.1.               Indemnification..............................................................15

ARTICLE 9 MISCELLANEOUS .........................................................................................16

         SECTION 9.1.               Successors and Assigns.......................................................16

         SECTION 9.2.               Amendments...................................................................16

         SECTION 9.3.               Notices......................................................................16

         SECTION 9.4.               Benefit......................................................................17

         SECTION 9.5.               Governing Law................................................................17
</TABLE>

                                     -iii-
<PAGE>   5
                               GUARANTEE AGREEMENT

                  This GUARANTEE AGREEMENT (the "Guarantee"), dated as of ______
__, 20___, is executed and delivered by U.S. BANCORP, a Delaware corporation
(the "Guarantor"), and WILMINGTON TRUST COMPANY, a Delaware banking corporation,
as trustee (the "Guarantee Trustee"), for the benefit of the Holders (as defined
herein) from time to time of the Securities (as defined herein) of USB CAPITAL
______, a Delaware statutory business trust (the "Trust").

                                    RECITALS

                  WHEREAS, pursuant to the Trust Agreement (as defined herein),
the Trust may issue up to $___________ aggregate liquidation amount of capital
securities, having a liquidation amount of $___ per security and designated the
"_____% Trust Preferred Securities" of the Trust (the "Capital Securities") and
up to $_____________ aggregate liquidation amount of common securities, having a
liquidation amount of $___ per security and designated the "_____% Common
Securities" of the Trust (the "Common Securities" and, together with the Capital
Securities, the "Securities");

                  WHEREAS, as incentive for the Holders to purchase the
Securities, the Guarantor desires irrevocably and unconditionally to agree, to
the extent set forth in this Guarantee, to pay to the Holders of the Securities
the Guarantee Payments (as defined herein) and to make certain other payments on
the terms and conditions set forth herein; and

                  WHEREAS, if a Trust Enforcement Event (as defined herein) has
occurred and is continuing, the rights of holders of the Common Securities to
receive Guarantee Payments (as defined herein) under this Guarantee are
subordinated to the rights of Holders of Capital Securities to receive Guarantee
Payments under this Guarantee;

                  NOW, THEREFORE, in consideration of the purchase by each
Holder of Securities, which purchase the Guarantor hereby agrees shall benefit
the Guarantor, the Guarantor executes and delivers this Guarantee for the
benefit of the Holders.

                                   ARTICLE 1

                         INTERPRETATION AND DEFINITIONS

         SECTION 1.1. Interpretation and Definitions. In this Guarantee, unless
the context otherwise requires:

                  (a) capitalized terms used in this Guarantee but not defined
         in the preamble above have the respective meanings assigned to them in
         this Section 1.1;

                  (b) a term defined anywhere in this Guarantee has the same
         meaning throughout;

                                      -1-
<PAGE>   6
                  (c) all references to "the Guarantee" or "this Guarantee" are
         to this Guarantee as modified, supplemented or amended from time to
         time;

                  (d) all references in this Guarantee to Articles, Sections and
         Recitals are to Articles, Sections and Recitals of this Guarantee,
         unless otherwise specified;

                  (e) unless otherwise defined in this Guarantee, a term defined
         in the Trust Indenture Act has the same meaning when used in this
         Guarantee;

                  (f) a reference to the singular includes the plural and vice
         versa and a reference to any masculine form of a term shall include the
         feminine form of a term, as applicable; and

                  (g) the following terms have the following meanings:

               "Affiliate" has the same meaning as given to that term in Rule
405 of the Securities Act of 1933, as amended, or any successor rule thereunder.

               "Business Day" has the meaning specified in the Trust Agreement.

               "Capital Securities" has the meaning specified in the Recitals
hereto.

               "Common Securities" has the meaning specified in the Recitals
hereto.

               "Common Stock" means the common stock, par value $0.01 per share,
of the Guarantor.

               "Corporate Trust Office" means the principal office of the
Guarantee Trustee at which at any particular time its corporate trust business
shall be administered, which office at the date of execution of this Guarantee
is located at 1100 North Market, Wilmington, Delaware 19890, Attention:
Corporate Trust Administration.

               "Debentures" means the series of junior subordinated debentures
to be issued by U.S. Bancorp designated the "______% Junior Subordinated
Debentures due ______ __, ____", held by the Property Trustee as defined in the
Trust Agreement.

               "Global Security" means a fully registered, global Capital
Security, as defined in the Indenture, representing the Capital Securities.

               "Guarantee Event of Default" means a default by the Guarantor on
any of its payment or other obligations under this Guarantee.

               "Guarantee Payments" means the following payments or
distributions, without duplication, with respect to the Securities, to the
extent not paid by or on behalf of the Trust: (i) any accumulated and unpaid
Distributions (as defined in the Trust Agreement) that are required to be paid
on such Securities to the extent the Trust has sufficient funds available
therefor at the time, (ii) the redemption price, including all accumulated and
unpaid Distributions

                                      -2-
<PAGE>   7
to the date of redemption, with respect to any Securities called for redemption
by the Trust, to the extent the Trust shall have sufficient funds available
therefor at the time or (iii) upon a voluntary or involuntary dissolution,
winding-up or termination of the Trust (other than in connection with the
distribution of Debentures to the Holders in exchange for Securities as provided
in the Trust Agreement), the lesser of (a) the aggregate of the liquidation
amount and all accumulated and unpaid Distributions on the Securities to the
date of payment, to the extent the Trust has sufficient funds available therefor
and (b) the amount of assets of the Trust remaining available for distribution
to Holders in liquidation of the Trust (in either case, the "Liquidation
Distribution").

                  "Guarantee Trustee" means Wilmington Trust Company, until a
Successor Guarantee Trustee has been appointed and has accepted such appointment
pursuant to the terms of this Guarantee and thereafter means each such Successor
Guarantee Trustee.

                  "Holder" means any holder of Securities, as registered on the
books and records of the Trust; provided, however, that, in determining whether
the Holders of the requisite percentage of Capital Securities have given any
request, notice, consent or waiver hereunder, "Holder" shall not include the
Guarantor or any Affiliate of the Guarantor or any other obligor on the Capital
Securities.

                  "Indenture" means the Indenture, dated as of November 15,
1996, by and between U.S. Bancorp and Wilmington Trust Company, as Trustee, and
any indenture supplemental thereto pursuant to which the Debentures are to be
issued to the Property Trustee, as defined in the Trust Agreement.

                  "List of Holders" has the meaning assigned to it in Section
2.2 hereof.

                  "Majority in Liquidation Amount" means, except as provided in
the terms of the Capital Securities or by the Trust Indenture Act, Holder(s) of
outstanding Securities, voting together as a single class, or, as the context
may require, Holders of outstanding Capital Securities or Holders of outstanding
Common Securities, voting separately as a class, who are the record owners of
more than 50% of the aggregate liquidation amount (including the stated amount
that would be paid on redemption, liquidation or otherwise, plus accumulated and
unpaid Distributions to the date upon which the voting percentages are
determined) of all outstanding Securities of the relevant class. In determining
whether the Holders of the requisite amount of Securities have voted, Securities
which are owned by the Guarantor or any Affiliate of the Guarantor or any other
obligor on the Securities shall be disregarded for the purpose of any such
determination.

                  "Officers' Certificate" means, with respect to any Person, a
certificate signed on behalf of such Person by two Authorized Officers (as
defined in the Trust Agreement) of such Person. Any Officers' Certificate
delivered with respect to compliance with a condition or covenant provided for
in this Guarantee shall include:

                  (i) a statement that each officer signing the Officers'
         Certificate has read the covenant or condition and the definitions
         relating thereto;

                                      -3-
<PAGE>   8
                  (ii) a brief statement of the nature and scope of the
         examination or investigation undertaken by each officer on behalf of
         such Person in rendering the Officers' Certificate;

                  (iii) a statement that each such officer has made such
         examination or investigation as, in such officer's opinion, is
         necessary to enable such officer on behalf of such Person to express an
         informed opinion as to whether or not such covenant or condition has
         been complied with; and

                  (iv) a statement as to whether, in the opinion of each such
         officer acting on behalf of such Person, such condition or covenant has
         been complied with.

                  "Person" means a legal person, including any individual,
corporation, estate, partnership, joint venture, association, joint stock
company, limited liability company, trust, unincorporated association, or
government or any agency or political subdivision thereof, or any other entity
of whatever nature.

                  "Redemption Price" has the meaning specified in the Trust
Agreement.

                  "Responsible Officer" means, with respect to the Guarantee
Trustee, any officer with direct responsibility for the administration of this
Guarantee and also means, with respect to a particular corporate trust matter,
any other officer to whom such matter is referred because of that officer's
knowledge of and familiarity with the particular subject.

                  "Securities" has the meaning specified in the Recitals hereto.

                  "Successor Guarantee Trustee" means a successor Guarantee
Trustee possessing the qualifications to act as Guarantee Trustee under Section
4.1.

                  "Trust Agreement" means the Amended and Restated Trust
Agreement, dated as of the date hereof, as amended, modified or supplemented
from time to time, among the trustees of the Trust named therein, the Guarantor,
as sponsor, and the Holders, from time to time, of undivided beneficial
ownership interests in the assets of the Trust.

                   "Trust Enforcement Event" in respect of the Securities means
an Indenture Event of Default (as defined in the Indenture) has occurred and is
continuing in respect of the Debentures.

                  "Trust Indenture Act" means the Trust Indenture Act of 1939,
as amended from time to time, or any successor legislation.

                                      -4-
<PAGE>   9
                                   ARTICLE 2

                               TRUST INDENTURE ACT

         SECTION 2.1. Trust Indenture Act; Application. (a) This Guarantee is
subject to the provisions of the Trust Indenture Act that are required to be
part of this Guarantee and shall, to the extent applicable, be governed by such
provisions.

         (b) If and to the extent that any provision of this Guarantee limits,
qualifies or conflicts with the duties imposed by Sections 310 to 317,
inclusive, of the Trust Indenture Act, such imposed duties shall control.

         SECTION 2.2. Lists of Holders of Securities. (a) The Guarantor shall
provide the Guarantee Trustee (i) except while the Capital Securities are
represented by one or more Global Securities, at least two Business Days prior
to the date for payment of Distributions, a list, in such form as the Guarantee
Trustee may reasonably require, of the names and addresses of the Holders of the
Securities ("List of Holders") as of the record date relating to the payment of
such Distributions, and (ii) at any other time, within 30 days of receipt by the
Guarantor of a written request from the Guarantee Trustee for a List of Holders
as of a date no more than 15 days before such List of Holders is given to the
Guarantee Trustee; provided that the Guarantor shall not be obligated to provide
such List of Holders at any time the List of Holders does not differ from the
most recent List of Holders given to the Guarantee Trustee by the Guarantor. The
Guarantee Trustee shall preserve, in as current a form as is reasonably
practicable, all information contained in Lists of Holders given to it, provided
that the Guarantee Trustee may destroy any List of Holders previously given to
it on receipt of a new List of Holders.

         (b) The Guarantee Trustee shall comply with its obligations under
Sections 311(a), 311(b) and 312(b) of the Trust Indenture Act.

         SECTION 2.3. Reports by Guarantee Trustee. Within 60 days after _______
___ of each year (commencing with the year of the first anniversary of the
issuance of the Securities), the Guarantee Trustee shall provide to the Holders
of the Securities such reports as are required by Section 313 of the Trust
Indenture Act (if any) in the form and in the manner provided by Section 313 of
the Trust Indenture Act. The Guarantee Trustee shall also comply with the
requirements of Section 313(d) of the Trust Indenture Act.

         SECTION 2.4. Periodic Reports to Guarantee Trustee. The Guarantor shall
provide to the Guarantee Trustee such documents, reports and information as
required by Section 314(a) (if any) of the Trust Indenture Act and the
compliance certificate required by Section 314(a) of the Trust Indenture Act in
the form, in the manner and at the times required by Section 314(a) of the Trust
Indenture Act, but in no event later than 120 days after the end of each
calendar year.

         SECTION 2.5. Evidence of Compliance with Conditions Precedent. The
Guarantor shall provide to the Guarantee Trustee such evidence of compliance
with any conditions precedent, if any, provided for in this Guarantee that
relate to any of the matters set forth in

                                      -5-
<PAGE>   10
Section 314(c) of the Trust Indenture Act. Any certificate or opinion required
to be given by an officer pursuant to Section 314(c)(1) may be given in the form
of an Officers' Certificate.

         SECTION 2.6. Guarantee Event of Default; Waiver. The Holders of a
Majority in Liquidation Amount of the Capital Securities may, by vote or written
consent, on behalf of the Holders of all of the Securities, waive any past
Guarantee Event of Default and its consequences. Upon such waiver, any such
Guarantee Event of Default shall cease to exist, and any Guarantee Event of
Default arising therefrom shall be deemed to have been cured, for every purpose
of this Guarantee, but no such waiver shall extend to any subsequent or other
default or Guarantee Event of Default or impair any right consequent thereon.

         SECTION 2.7. Guarantee Event of Default; Notice. (a) The Guarantee
Trustee shall, within 90 days after the occurrence of a Guarantee Event of
Default actually known to a Responsible Officer of the Guarantee Trustee,
transmit by mail, first class postage prepaid, to the Holders of the Securities,
notices of all such Guarantee Events of Default, unless such defaults have been
cured before the giving of such notice; provided, that the Guarantee Trustee
shall be protected in withholding such notice if and so long as a Responsible
Officer of the Guarantee Trustee in good faith determines that the withholding
of such notice is in the interests of the Holders of the Securities.

         (b) The Guarantee Trustee shall not be deemed to have knowledge of any
Guarantee Event of Default unless the Guarantee Trustee shall have received
written notice thereof or a Responsible Officer of the Guarantee Trustee charged
with the administration of this Guarantee Agreement shall have obtained actual
knowledge thereof.

         SECTION 2.8. Conflicting Interests. The Trust Agreement shall be deemed
to be specifically described in this Guarantee for the purposes of clause (i) of
the first proviso contained in Section 310(b) of the Trust Indenture Act.

         SECTION 2.9. Disclosure of Information. The disclosure of information
as to the names and addresses of the Holders of the Securities in accordance
with Section 312 of the Trust Indenture Act, regardless of the source from which
such information was derived, shall not be deemed to be a violation of any
existing law, or any law hereafter enacted which does not specifically refer to
Section 312 of the Trust Indenture Act, nor shall the Guarantee Trustee be held
accountable by reason of mailing any material pursuant to a request made under
Section 312(b) of the Trust Indenture Act.

         SECTION 2.10. Guarantee Trustee May File Proofs of Claim. Upon the
occurrence of a Guarantee Event of Default, the Guarantee Trustee is hereby
authorized to (a) recover judgment, in its own name and as trustee of an express
trust, against the Guarantor for the whole amount of any Guarantee Payments
remaining unpaid and (b) file such proofs of claim and other papers or documents
as may be necessary or advisable in order to have its claims and those of the
Holders of the Securities allowed in any judicial proceedings relative to the
Guarantor, its creditors or its property.

                                      -6-
<PAGE>   11
                                   ARTICLE 3

                          POWERS, DUTIES AND RIGHTS OF
                                GUARANTEE TRUSTEE

         SECTION 3.1. Powers and Duties of Guarantee Trustee.

         (a) This Guarantee shall be held by the Guarantee Trustee on behalf of
the Trust for the benefit of the Holders of the Securities, and the Guarantee
Trustee shall not transfer this Guarantee to any Person except a Holder of
Securities exercising his or her rights pursuant to Section 5.4(b) or to a
Successor Guarantee Trustee on acceptance by such Successor Guarantee Trustee of
its appointment to act as Successor Guarantee Trustee. The right, title and
interest of the Guarantee Trustee in and to this Guarantee shall automatically
vest in any Successor Guarantee Trustee, and such vesting and succession of
title shall be effective whether or not conveyance documents have been executed
and delivered pursuant to the appointment of such Successor Guarantee Trustee.

         (b) If a Guarantee Event of Default actually known to a Responsible
Officer of the Guarantee Trustee has occurred and is continuing, the Guarantee
Trustee shall enforce this Guarantee for the benefit of the Holders of the
Securities.

         (c) The Guarantee Trustee, before the occurrence of any Guarantee Event
of Default and after the curing of all Guarantee Events of Default that may have
occurred, shall undertake to perform only such duties as are specifically set
forth in this Guarantee, and no implied covenants shall be read into this
Guarantee against the Guarantee Trustee. In case a Guarantee Event of Default
has occurred (that has not been cured or waived pursuant to Section 2.6) and is
actually known to a Responsible Officer of the Guarantee Trustee, the Guarantee
Trustee shall exercise such of the rights and powers vested in it by this
Guarantee, and use the same degree of care and skill in its exercise thereof, as
a prudent person would exercise or use under the circumstances in the conduct of
his or her own affairs.

         (d) No provision of this Guarantee shall be construed to relieve the
Guarantee Trustee from liability for its own negligent action, its own negligent
failure to act, or its own willful misconduct, except that:

                  (i) prior to the occurrence of any Guarantee Event of Default
         and after the curing or waiving of all such Guarantee Events of Default
         that may have occurred:

                    (A)  the duties and obligations of the Guarantee Trustee
                         shall be determined solely by the express provisions of
                         this Guarantee, and the Guarantee Trustee shall not be
                         liable except for the performance of such duties and
                         obligations as are specifically set forth in this
                         Guarantee, and no implied covenants or obligations
                         shall be read into this Guarantee against the Guarantee
                         Trustee; and

                                      -7-
<PAGE>   12
                    (B)  in the absence of bad faith on the part of the
                         Guarantee Trustee, the Guarantee Trustee may
                         conclusively rely, as to the truth of the statements
                         and the correctness of the opinions expressed therein,
                         upon any certificates or opinions furnished to the
                         Guarantee Trustee and conforming to the requirements of
                         this Guarantee; but in the case of any such
                         certificates or opinions that by any provision hereof
                         are specifically required to be furnished to the
                         Guarantee Trustee, the Guarantee Trustee shall be under
                         a duty to examine the same to determine whether or not
                         they conform to the requirements of this Guarantee;

                  (ii) the Guarantee Trustee shall not be liable for any error
         of judgment made in good faith by a Responsible Officer of the
         Guarantee Trustee, unless it shall be proved that the Guarantee Trustee
         was negligent in ascertaining the pertinent facts upon which such
         judgment was made;

                  (iii) the Guarantee Trustee shall not be liable with respect
         to any action taken or omitted to be taken by it in good faith in
         accordance with the direction of the Holders of not less than a
         Majority in Liquidation Amount of the Securities relating to the time,
         method and place of conducting any proceeding for any remedy available
         to the Guarantee Trustee, or exercising any trust or power conferred
         upon the Guarantee Trustee under this Guarantee; and

                  (iv) no provision of this Guarantee shall require the
         Guarantee Trustee to expend or risk its own funds or otherwise incur
         personal financial liability in the performance of any of its duties or
         in the exercise of any of its rights or powers, if the Guarantee
         Trustee shall have reasonable grounds for believing that the repayment
         of such funds or liability is not reasonably assured to it under the
         terms of this Guarantee or if the Guarantee Trustee shall have
         reasonable grounds for believing that an indemnity, reasonably
         satisfactory to the Guarantee Trustee, against such risk or liability
         is not reasonably assured to it under the terms of this Guarantee.

         SECTION 3.2. Certain Rights of Guarantee Trustee. (a) Subject to the
provisions of Section 3.1:

                  (i) The Guarantee Trustee may conclusively rely, and shall be
         fully protected in acting or refraining from acting upon, any
         resolution, certificate, statement, instrument, opinion, report,
         notice, request, direction, consent, order, bond, debenture, note,
         other evidence of indebtedness or other paper or document believed by
         it to be genuine and to have been signed, sent or presented by the
         proper party or parties;

                  (ii) Any direction or act of the Guarantor contemplated by
         this Guarantee shall be sufficiently evidenced by an Officers'
         Certificate;

                                      -8-
<PAGE>   13
                  (iii) Whenever, in the administration of this Guarantee, the
         Guarantee Trustee shall deem it desirable that a matter be proved or
         established before taking, suffering or omitting any action hereunder,
         the Guarantee Trustee (unless other evidence is herein specifically
         prescribed) may, in the absence of bad faith on its part, request and
         conclusively rely upon an Officers' Certificate which, upon receipt of
         such request, shall be promptly delivered by the Guarantor;

                  (iv) The Guarantee Trustee shall have no duty to see to any
         recording, filing or registration or any instrument (or any
         rerecording, refiling or re-registration thereof);

                  (v) The Guarantee Trustee may consult with counsel, and the
         advice or opinion of such counsel with respect to legal matters shall
         be full and complete authorization and protection in respect of any
         action taken, suffered or omitted by it hereunder in good faith and in
         accordance with such advice or opinion. Such counsel may be counsel to
         the Guarantor or any of its Affiliates and may include any of its
         employees. The Guarantee Trustee shall have the right at any time to
         seek instructions concerning the administration of this Guarantee from
         any court of competent jurisdiction;

                  (vi) The Guarantee Trustee shall be under no obligation to
         exercise any of the rights or powers vested in it by this Guarantee at
         the request or direction of any Holder, unless such Holder shall have
         provided to the Guarantee Trustee such security and indemnity,
         reasonably satisfactory to the Guarantee Trustee, against the costs,
         expenses (including attorneys' fees and expenses and the expenses of
         the Guarantee Trustee's agents, nominees or custodians) and liabilities
         that might be incurred by it in complying with such request or
         direction, including such reasonable advances as may be requested by
         the Guarantee Trustee; provided, that nothing contained in this Section
         3.2(a)(vi) shall be taken to relieve the Guarantee Trustee, upon the
         occurrence of a Guarantee Event of Default, of its obligation to
         exercise the rights and powers vested in it by this Guarantee;

                  (vii) The Guarantee Trustee shall not be bound to make any
         investigation into the facts or matters stated in any resolution,
         certificate, statement, instrument, opinion, report, notice, request,
         direction, consent, order, bond, debenture, note, other evidence of
         indebtedness or other paper or document, but the Guarantee Trustee, in
         its discretion, may make such further inquiry or investigation into
         such facts or matters as it may see fit;

                  (viii) The Guarantee Trustee may execute any of the trusts or
         powers hereunder or perform any duties hereunder either directly or by
         or through agents, nominees, custodians or attorneys, and the Guarantee
         Trustee shall not be responsible for any misconduct or negligence on
         the part of any agent or attorney appointed with due care by it
         hereunder;

                                      -9-
<PAGE>   14
                  (ix) Any action taken by the Guarantee Trustee or its agents
         hereunder shall bind the Holders, and the signature of the Guarantee
         Trustee or its agents alone shall be sufficient and effective to
         perform any such action. No third party shall be required to inquire as
         to the authority of the Guarantee Trustee to so act or as to its
         compliance with any of the terms and provisions of this Guarantee, both
         of which shall be conclusively evidenced by the Guarantee Trustee's or
         its agent's taking such action; and

                  (x) Whenever in the administration of this Guarantee, the
         Guarantee Trustee shall deem it desirable to receive instructions with
         respect to enforcing any remedy or right or taking any other action
         hereunder, the Guarantee Trustee (i) may request written instructions
         from the Holders of a Majority in Liquidation Amount of the Securities,
         (ii) may refrain from enforcing such remedy or right or taking such
         other action until such written instructions are received and (iii)
         shall be protected in conclusively relying on or acting in accordance
         with such written instructions.

         (b) No provision of this Guarantee shall be deemed to impose any duty
or obligation on the Guarantee Trustee to perform any act or acts or exercise
any right, power, duty or obligation conferred or imposed on it in any
jurisdiction in which it shall be illegal, or in which the Guarantee Trustee
shall be unqualified or incompetent to act in accordance with applicable law, to
perform any such act or acts or to exercise any such right, power, duty or
obligation. No permissive power or authority available to the Guarantee Trustee
shall be construed to be a duty.

                                   ARTICLE 4

                                GUARANTEE TRUSTEE

         SECTION 4.1. Guarantee Trustee; Eligibility.

                  (a) There shall be at all times a Guarantee Trustee which
         shall:

                           (i) not be an Affiliate of the Guarantor; and

                           (ii) be a corporation organized and doing business
                  under the laws of the United States of America or any state or
                  territory thereof or of the District of Columbia, or a
                  corporation or other Person permitted by the Securities and
                  Exchange Commission to act as an institutional trustee under
                  the Trust Indenture Act, authorized under such laws to
                  exercise corporate trust powers, having a combined capital and
                  surplus of at least 50 million U.S. dollars ($50,000,000), and
                  subject to supervision or examination by federal, state,
                  territorial or District of Columbia authority. If such
                  corporation publishes reports of condition at least annually,
                  pursuant to law or to the requirements of the supervising or
                  examining authority referred to above, then, for the purposes
                  of this Section 4.1(a)(ii), the combined capital and surplus
                  of such corporation shall be deemed to be its

                                      -10-
<PAGE>   15
                  combined capital and surplus as set forth in its most recent
                  report of condition so published.

                  (b) If at any time the Guarantee Trustee shall cease to be
         eligible to so act under Section 4.1(a), the Guarantee Trustee shall
         immediately resign in the manner and with the effect set out in Section
         4.2(c).

                  (c) If the Guarantee Trustee has or shall acquire any
         "conflicting interest" within the meaning of Section 310(b) of the
         Trust Indenture Act, the Guarantee Trustee and Guarantor shall in all
         respects comply with the provisions of Section 310(b) of the Trust
         Indenture Act.

         SECTION 4.2. Appointment, Removal and Resignation of Guarantee Trustee.

         (a) Subject to Section 4.2(b), unless a Guarantee Event of Default
shall have occurred and be continuing, the Guarantee Trustee may be appointed or
removed with or without cause at any time by the Guarantor.

         (b) The Guarantee Trustee shall not be removed in accordance with
Section 4.2(a) until a Successor Guarantee Trustee has been appointed and has
accepted such appointment by written instrument executed by such Successor
Guarantee Trustee and delivered to the Guarantor.

         (c) The Guarantee Trustee appointed to office shall hold such office
until a Successor Guarantee Trustee shall have been appointed or until its
removal or resignation. The Guarantee Trustee may resign from office (without
need for prior or subsequent accounting) by an instrument in writing executed by
the Guarantee Trustee and delivered to the Guarantor, which resignation shall
not take effect until a Successor Guarantee Trustee has been appointed and has
accepted such appointment by instrument in writing executed by such Successor
Guarantee Trustee and delivered to the Guarantor and the resigning Guarantee
Trustee.

         (d) If no Successor Guarantee Trustee shall have been appointed and
accepted appointment as provided in this Section 4.2 within 60 days after
delivery to the Guarantor of an instrument of removal or resignation, the
removed or resigning Guarantee Trustee may petition any court of competent
jurisdiction for appointment of a Successor Guarantee Trustee. Such court may
thereupon, after prescribing such notice, if any, as it may deem proper, appoint
a Successor Guarantee Trustee.

         (e) No Guarantee Trustee shall be liable for the acts or omissions to
act of any Successor Guarantee Trustee.

         (f) Upon termination of this Guarantee or removal or resignation of the
Guarantee Trustee pursuant to this Section 4.2, the Guarantor shall pay to the
Guarantee Trustee all amounts owing for fees and reimbursement of expenses which
have accrued to the date of such termination, removal or resignation.

                                      -11-
<PAGE>   16
                                    ARTICLE 5

                                    GUARANTEE

         SECTION 5.1. Guarantee.

         The Guarantor irrevocably and unconditionally agrees to pay in full to
the Holders the Guarantee Payments (without duplication of amounts theretofore
paid by the Trust), as and when due, regardless of any defense, right of set-off
or counterclaim that the Trust may have or assert. The Guarantor's obligation to
make a Guarantee Payment may be satisfied by direct payment of the required
amounts by the Guarantor to the Holders or by causing the Trust to pay such
amounts to the Holders. Notwithstanding anything to the contrary herein, the
Guarantor retains all of its rights under the Indenture to extend the interest
payment period on the Debentures pursuant to Section 3.11 thereof and the
Guarantor shall not be obligated hereunder to make any Guarantee Payments during
any Extension Period (as defined in the certificate evidencing the Debentures)
with respect to the Distributions (as defined in the Trust Agreement) on the
Securities.

         SECTION 5.2. Waiver of Notice and Demand.

         The Guarantor hereby waives notice of acceptance of this Guarantee and
of any liability to which it applies or may apply, presentment, demand for
payment, any right to require a proceeding first against the Trust or any other
Person before proceeding against the Guarantor, protest, notice of nonpayment,
notice of dishonor, notice of redemption and all other notices and demands.

         SECTION 5.3. Obligations Not Affected.

         The obligations, covenants, agreements and duties of the Guarantor
under this Guarantee shall be absolute and unconditional and shall remain in
full force and effect until the entire liquidation amount of all outstanding
Securities shall have been paid and such obligation shall in no way be affected
or impaired by reason of the happening from time to time of any event, including
without limitation, the following, whether or not with notice to, or the consent
of, the Guarantor:

                  (a) The release or waiver, by operation of law or otherwise,
         of the performance or observance by the Trust of any express or implied
         agreement, covenant, term or condition relating to the Securities to be
         performed or observed by the Trust;

                  (b) The extension of time for the payment by the Trust of all
         or any portion of the Distributions, Redemption Price, Liquidation
         Distribution or any other sums payable under the terms of the
         Securities or the extension of time for the performance of any other
         obligation under, arising out of, or in connection with the Securities
         (other than an extension of time for payment of Distributions,
         Redemption Price, Liquidation Distribution or other sum payable that
         results from the extension of any interest payment period on the
         Debentures);

                                      -12-
<PAGE>   17
                  (c) Any failure, omission, delay or lack of diligence on the
         part of the Property Trustee or the Holders to enforce, assert or
         exercise any right, privilege, power or remedy conferred on the
         Property Trustee or the Holders pursuant to the terms of the
         Securities, or any action on the part of the Trust granting indulgence
         or extension of any kind;

                  (d) The voluntary or involuntary liquidation, dissolution,
         sale of any collateral, receivership, insolvency, bankruptcy,
         assignment for the benefit of creditors, reorganization, arrangement,
         composition or readjustment of debt of, or other similar proceedings
         affecting, the Trust or any of the assets of the Trust;

                  (e) Any invalidity of, or defect or deficiency in, the
         Securities;

                  (f) The settlement or compromise of any obligation guaranteed
         hereby or hereby incurred; or

                  (g) Any other circumstance whatsoever that might otherwise
         constitute a legal or equitable discharge or defense of a guarantor, it
         being the intent of this Section 5.3 that the obligations of the
         Guarantor hereunder shall be absolute and unconditional under any and
         all circumstances.

         There shall be no obligation of the Guarantee Trustee or the Holders to
give notice to, or obtain consent of the Guarantor or any other Person with
respect to the happening of any of the foregoing.

         No setoff, counterclaim, reduction or diminution of any obligation, or
any defense of any kind or nature that the Guarantor has or may have against any
Holder shall be available hereunder to the Guarantor against such Holder to
reduce the payments to it under this Guarantee.

         SECTION 5.4. Rights of Holders.

         (a) The Holders of at least a Majority in Liquidation Amount of the
Securities have the right to direct the time, method and place of conducting any
proceeding for any remedy available to the Guarantee Trustee in respect of this
Guarantee or to direct the exercise of any trust or power conferred upon the
Guarantee Trustee under this Guarantee.

         (b) If the Guarantee Trustee fails to enforce this Guarantee, then any
Holder of Securities may, subject to the subordination provisions of Section
6.2, institute a legal proceeding directly against the Guarantor to enforce the
Guarantee Trustee's rights under this Guarantee without first instituting a
legal proceeding against the Trust, the Guarantee Trustee or any other person or
entity. In addition, if the Guarantor has failed to make a Guarantee Payment, a
Holder of Securities may, subject to the subordination provisions of Section
6.2, directly institute a proceeding against the Guarantor for enforcement of
the Guarantee for such payment to the Holder of the Securities of the principal
of or interest on the Debentures on or after the respective due dates specified
in the Debentures, and the amount of the payment will be based on the Holder's
pro rata share of the amount due and owing on all of the Securities. The
Guarantor

                                      -13-
<PAGE>   18
hereby waives any right or remedy to require that any action on this Guarantee
be brought first against the Trust or any other person or entity before
proceeding directly against the Guarantor.

         SECTION 5.5. Guarantee of Payment.

         This Guarantee creates a guarantee of payment and not of collection.

         SECTION 5.6. Subrogation.

         The Guarantor shall be subrogated to all (if any) rights of the Holders
of Securities against the Trust in respect of any amounts paid to such Holders
by the Guarantor under this Guarantee; provided, however, that the Guarantor
shall not (except to the extent required by mandatory provisions of law) be
entitled to enforce or exercise any right that it may acquire by way of
subrogation or any indemnity, reimbursement or other agreement, in all cases as
a result of payment under this Guarantee, if at the time of any such payment,
any amounts are due and unpaid under this Guarantee. If any amount shall be paid
to the Guarantor in violation of the preceding sentence, the Guarantor agrees to
hold such amount in trust for the Holders and to pay over such amount to the
Guarantee Trustee for the benefit of the Holders.

         SECTION 5.7. Independent Obligations.

         The Guarantor acknowledges that its obligations hereunder are
independent of the obligations of the Trust with respect to the Securities, and
that the Guarantor shall be liable as principal and as debtor hereunder to make
Guarantee Payments pursuant to the terms of this Guarantee notwithstanding the
occurrence of any event referred to in subsections 5.3(a) through 5.3(g),
inclusive, hereof.

                                    ARTICLE 6

                    LIMITATION OF TRANSACTIONS; SUBORDINATION

         SECTION 6.1. Limitation of Transactions.

         So long as any Securities remain outstanding, if (i) there shall have
occurred an event of default under the Indenture with respect to the Debentures,
(ii) there shall be a Guarantee Event of Default or (iii) the Guarantor shall
have given notice of its election of an Extension Period as provided in the
certificate evidencing the Debentures and shall not have rescinded such notice,
or such Extension Period or any extension thereof shall be continuing, then the
Guarantor shall not, and shall not permit any subsidiary of the Guarantor, to
(x) declare or pay any dividends or distributions on, or redeem, purchase,
acquire or make a liquidation payment with respect to, any of the Guarantor's
capital stock or (y) make any payment of principal, interest or premium, if any,
on or repay, repurchase or redeem any debt securities of the Guarantor that rank
pari passu with or junior in interest to the Debentures or make any guarantee
payments with respect to any guarantee by the Guarantor of the debt securities
of any subsidiary of the Guarantor if such guarantee ranks pari passu with or
junior in interest to the Debentures (other than (a) dividends or distributions
in Common Stock of the Guarantor, (b) any declaration of a dividend in
connection with the implementation of a rights plan or the issuance

                                      -14-
<PAGE>   19
of stock under any such plan or the redemption or repurchase of any such rights
pursuant thereto, (c) payments under this Guarantee and (d) purchases of Common
Stock related to the issuance of Common Stock or rights under any of the
Company's benefits plans for its directors, officers or employees).

         SECTION 6.2. Ranking.

         This Guarantee will constitute an unsecured obligation of the Guarantor
and will rank subordinate and junior in right of payment to all Senior and
Subordinated Debt (as defined in the Indenture) of the Guarantor in the same
manner and to the same extent as set forth in Article XIII of the Indenture.

         SECTION 6.3. Subordination of Common Securities.

         If a Trust Enforcement Event has occurred and is continuing under the
Trust Agreement, the rights of the holders of the Common Securities to receive
Guarantee Payments hereunder shall be subordinated to the rights of the Holders
of the Capital Securities to receive Guarantee Payments under this Guarantee.

                                    ARTICLE 7

                                   TERMINATION

         SECTION 7.1. Termination.

         This Guarantee shall terminate upon (i) full payment of the Redemption
Price of all Securities, (ii) distribution of the Debentures to the Holders of
all the Securities or (iii) full payment of the amounts payable in accordance
with the Trust Agreement upon liquidation of the Trust. Notwithstanding the
foregoing, this Guarantee will continue to be effective or will be reinstated,
as the case may be, if at any time any Holder of Securities must restore payment
of any sums paid under the Securities or under this Guarantee.

                                    ARTICLE 8

                                 INDEMNIFICATION

         SECTION 8.1. Indemnification.

         The Guarantor agrees to indemnify each Indemnified Person for, and to
hold each Indemnified Person harmless against any loss, liability or expense
incurred without negligence or bad faith on its part, arising out of or in
connection with the acceptance or administration of the trust or trusts
hereunder, including the reasonable costs and expenses of defending itself
against, or investigating, any claim or liability in connection with the
exercise or performance of any of its powers or duties hereunder. The provisions
of this Section 8.1 shall survive the termination of this Guarantee or the
resignation or removal of the Guarantee Trustee.

                                      -15-
<PAGE>   20
                                   ARTICLE 9

                                  MISCELLANEOUS

         SECTION 9.1. Successors and Assigns.

         All guarantees and agreements contained in this Guarantee shall bind
the successors, assigns, receivers, trustees and representatives of the
Guarantor and shall inure to the benefit of the Holders of the Securities then
outstanding. Except in connection with a consolidation, merger or sale involving
the Guarantor that is permitted under Article VIII of the Indenture and pursuant
to which the successor or assignee agrees in writing to perform the Guarantor's
obligations hereunder, the Guarantor shall not assign its obligations hereunder.

         SECTION 9.2. Amendments.

         Except with respect to any changes that do not materially adversely
affect the rights of the Holders (in which case no consent of the Holders will
be required), this Guarantee may not be amended without the prior approval of
the Holders of at least a Majority in Liquidation Amount of the Securities. The
provisions of Section 11.2 of the Trust Agreement with respect to meetings of,
and action by written consent of, the Holders of the Securities apply to the
giving of such approval.

         SECTION 9.3. Notices.

         All notices provided for in this Guarantee shall be in writing, duly
signed by the party giving such notice, and shall be delivered by hand,
telecopied or mailed by registered or certified mail, as follows:

                  (a) If given to the Guarantee Trustee, at the Guarantee
         Trustee's mailing address set forth below (or such other address as the
         Guarantee Trustee may give notice of to the Guarantor and the Holders
         of the Securities):

                           Wilmington Trust Company
                           1100 North Market
                           Wilmington, Delaware 19890

                           Facsimile No.: (302) 651-8882
                           Attention: Corporate Trust Administration

                  (b) If given to the Guarantor, at the Guarantor's mailing
         addresses set forth below (or such other address as the Guarantor may
         give notice of to the Guarantee Trustee and the Holders of the
         Securities):

                                      -16-
<PAGE>   21
                           U.S. Bancorp
                           601 Second Avenue South
                           Minneapolis, Minnesota 55402
                           Facsimile No.: (612) 973-0965
                           Attention:  Treasury Department

                  (c) If given to any Holder of Securities, at the address set
         forth on the books and records of the Trust.

         All such notices shall be deemed to have been given when received in
person, telecopied with receipt confirmed, or mailed by first class mail,
postage prepaid, except that if a notice or other document is refused delivery
or cannot be delivered because of a changed address of which no notice was
given, such notice or other document shall be deemed to have been delivered on
the date of such refusal or inability to deliver.

         SECTION 9.4. Benefit.

         This Guarantee is solely for the benefit of the Holders of the
Securities and, subject to Section 3.1(a), is not separately transferable from
the Securities.

         SECTION 9.5. Governing Law. THIS GUARANTEE SHALL BE GOVERNED BY AND
CONSTRUED AND INTERPRETED IN ACCORDANCE WITH THE LAW OF THE STATE OF NEW YORK.

                  IN WITNESS WHEREOF, this Guarantee is executed as of the day
and year first above written.

                                    U.S. BANCORP,
                                      as Guarantor

                                    By:
                                        ________________________________________
                                          Name:
                                          Title:

                                    WILMINGTON TRUST COMPANY,
                                      as Guarantee Trustee

                                    By:
                                        ________________________________________
                                          Name:
                                          Title:

                                      -17-<PAGE>   1
                                                                     EXHIBIT 4.1

================================================================================

                          THIRD SUPPLEMENTAL INDENTURE

                            Dated as of July 16, 2001

                                       to

                                    INDENTURE

                           Dated as of March 13, 2001

                                     between

                                NRG ENERGY, INC.

                                       and

                              THE BANK OF NEW YORK,

                                   as Trustee

================================================================================

<PAGE>   2

         THIRD SUPPLEMENTAL INDENTURE, dated as of July 16, 2001 (this "Third
Supplemental Indenture"), to the Indenture, dated as of March 13, 2001 (the
"Base Indenture"), between NRG ENERGY, INC., a Delaware corporation (the
"Company"), and THE BANK OF NEW YORK, a New York banking corporation (the
"Trustee"), as supplemented by the First Supplemental Indenture, dated as of
March 13, 2001 (the "First Supplemental Indenture"), between the Company and the
Trustee and the Second Supplemental Indenture, dated as of April 5, 2001 (the
"Second Supplemental Indenture"), between the Company and the Trustee.

         WHEREAS, the Company and the Trustee have heretofore executed and
delivered the Base Indenture to provide for the issuance from time to time of
Securities (as defined in the Base Indenture) of the Company, to be issued in
one or more Series (as defined in the Base Indenture);

         WHEREAS, Sections 2.1, 2.2 and 7.1 of the Base Indenture provide, among
other things, that the Company and the Trustee may enter into indentures
supplemental to the Base Indenture for, among other things, (i) the purpose of
establishing the designation, form, terms and provisions of Securities of any
Series as permitted by Sections 2.1, 2.2 and 7.1 of the Base Indenture and (ii)
the purpose of reopening a Series of Securities for issuances of additional
Securities of such Series;

         WHEREAS, the Company (i) desires the issuance of a new separate Series
of Securities to be designated as hereinafter provided and desires to reopen for
issuance of additional Securities the Series of Securities designated the 8.625%
Senior Notes due 2031 established by the Second Supplemental Indenture (the
"Senior Notes due 2031") and (ii) has requested the Trustee to enter into this
Third Supplemental Indenture for the purpose of establishing the designation,
form, terms and provisions of the Securities of such new Series and reopening
the Senior Notes due 2031;

         WHEREAS, all action on the part of the Company necessary to authorize
the issuance of said Securities under the Base Indenture and this Third
Supplemental Indenture has been duly taken.

         NOW, THEREFORE, THIS THIRD SUPPLEMENTAL INDENTURE WITNESSETH:

         That, in order to establish the designation, form, terms and provisions
of or reopen for issuance, and to authorize the authentication and delivery of,
said Securities, and in consideration of the acceptance of said Securities by
the Holders thereof and of other good and valuable consideration, the receipt
and sufficiency of which are hereby acknowledged, the parties hereto hereby
agree as follows:

<PAGE>   3

                                   ARTICLE I

                                  DEFINITIONS

         (a) Capitalized terms used herein and not otherwise defined herein
shall have the respective meanings ascribed thereto in the Base Indenture.

         (b) The rules of interpretation set forth in the Base Indenture shall
be applied hereto as if set forth in full herein.

         (c) For all purposes of this Third Supplemental Indenture, except as
otherwise expressly provided or unless the context otherwise requires, the
following terms shall have the following respective meanings (such meanings
shall apply equally to both the singular and plural forms of the respective
terms):

         "Change of Control" means the occurrence of one or more of the
following events: (i) Xcel or its successors ceases to own a majority of the
outstanding Voting Stock of the Issuer, (ii) at any time following the
occurrence of the event described in the preceding clause (i), a Person or group
(as that term is used in Section 13(d)(3) of the Exchange Act) of Persons (other
than Xcel) shall have become the beneficial owner directly or indirectly, or
shall have acquired the absolute power to direct the vote, of more than 35% of
the outstanding Voting Stock of the Issuer or (iii) during any twelve-month
period, individuals who at the beginning of such period constitute the Board of
Directors (together with any new directors whose election or nomination was
approved by a majority of the directors then in office who were either directors
at the beginning of such period or who were previously so approved) shall cease
for any reason to constitute a majority of the Board of Directors.
Notwithstanding the foregoing, a Change of Control shall be deemed not to have
occurred with respect to a Series of Securities if one or more of the above
events occurs or circumstances exist and, after giving effect thereto, the
Securities of such Series are rated Investment Grade.

         "Comparable Treasury Issue" means the United States Treasury security
selected by Banc of America Securities LLC or Deutsche Banc Alex. Brown Inc., or
any of their respective affiliates as having a maturity comparable to the
remaining term of the Notes that would be utilized, at the time of selection and
in accordance with customary financial practice, in pricing new issues of
corporate debt securities of comparable maturity to the remaining term of the
Senior Notes due 2006.

                                       2
<PAGE>   4

         "Comparable Treasury Price" means the average of three Reference
Treasury Dealer Quotations obtained by the Trustee in respect of the Senior
Notes due 2006 to be redeemed on the applicable redemption date.

         "Make Whole Amount" means, with respect to the Senior Notes due 2006 at
any time, the sum of the present values of the Remaining Scheduled Payments
discounted, on a semiannual basis (assuming a 360 day year consisting of twelve
30-day months), at a rate equal to the Treasury Rate plus 25 basis points. The
Make Whole Amount shall be computed as of the third Business Day prior to the
applicable redemption date, and certified, by an Investment Banker.

         "Notes" means the Senior Notes due 2006 and the Senior Notes due 2031.

         "Reference Treasury Dealer Quotation" means, with respect to each
Reference Treasury Dealer and any redemption date, the average, as determined by
the Trustee, of the bid and asked prices for the Comparable Treasury Issue
(expressed in each case as a percentage of its principal amount) quoted in
writing to t he Trustee by a Reference Treasury Dealer at 3:30 p.m., New York
City time, on the third Business Day preceding the redemption date.

         "Reference Treasury Dealers" means Banc of America Securities LLC and
Deutsche Banc Alex. Brown Inc. (so long as they continue to be primary U.S.
Government securities dealers) and any two other primary U.S. Government
securities dealers chosen by the Company. If Banc of America Securities LLC or
Deutsche Banc Alex. Brown Inc. ceases to be a primary U.S. Government securities
dealer, the Company will appoint in its place another nationally recognized
investment banking firm that is a primary U.S. Government securities dealer.

         "Remaining Scheduled Payments" means, with respect to each Senior Note
due 2006 that the Company is redeeming, the remaining scheduled payments of the
principal and interest that would be due after the related redemption date if
such Senior Note due 2006 were not redeemed. However, if the redemption date is
not a scheduled interest payment date with respect to that Senior Note due 2006,
the amount of the next succeeding scheduled interest payment on that Senior Note
due 2006 will be reduced by the amount of interest accrued on such Senior Note
due 2006 to the redemption date.

         "Senior Notes due 2006" shall have the meaning ascribed thereto in
Section 2.1(a) hereof.

                                       3
<PAGE>   5

         "Senior Notes due 2031" shall have the meaning ascribed thereto in the
recitals hereof.

         "Treasury Rate" means, with respect to any redemption date, an annual
rate equal to the semiannual equivalent yield to maturity of the Comparable
Treasury Issue, assuming a price for the Comparable Treasury Issue (expressed as
a percentage of its principal amount) equal to the Comparable Treasury Price for
the redemption date. The semiannual equivalent yield to maturity will be
computed as of the third Business Day immediately preceding the redemption date.

                                   ARTICLE II

           GENERAL TERMS AND CONDITIONS OF THE SENIOR NOTES DUE 2006

         SECTION 2.1 Designation and Principal Amount.

         (a) There is hereby authorized a new separate Series of Securities
designated the 6.75% Senior Notes due 2006 (the "Senior Notes due 2006").

         (b) The aggregate principal amount of the Senior Notes due 2006 shall
be limited to $340,000,000 (except that such Series of Securities may be
re-opened for issuance of additional Securities as provided in Article II of the
Base Indenture).

         (c) The Senior Notes due 2006 may be issued from time to time upon
written order of the Company to the Trustee for the authentication and delivery
of the Senior Notes due 2006 pursuant to Section 2.2 of the Base Indenture.

         (d) The Senior Notes due 2006 shall have and be subject to such other
terms as provided in the Base Indenture and shall be evidenced by one or more
Securities of that Series in the form of Exhibit A to the Base Indenture.

         (e) The Senior Notes due 2006 shall be issuable in minimum
denominations of $100,000 and integral multiples of $1,000 in excess thereof.

         SECTION 2.2 Maturity. The date upon which the Senior Notes due 2006
shall become due and payable at final maturity, together with any accrued and
unpaid interest, is July 15, 2006 (the "2006 Notes Maturity Date").

                                       4
<PAGE>   6

         SECTION 2.3 Interest.

         (a) The Senior Notes due 2006 will bear interest at the 2006 Notes
Interest Rate (as defined below) from July 16, 2001, until the principal thereof
becomes due and payable. Interest on the Senior Notes due 2006 will be payable
semi-annually in arrears on January 15 and July 15 of each year, commencing
January 15, 2002, to the Person in whose name any such Senior Note due 2006 or
any predecessor Note is registered, at the close of business on the regular
record date for such interest installment, which, in the case of a Global
Security, shall be the close of business on the January 1 and July 1 next
preceding such Interest Payment Date. Notwithstanding the foregoing sentence, if
the Notes are no longer in book-entry only form, the regular record dates for
the Notes shall be the January 1 and July 1 prior to the applicable Interest
Payment Date.

         (b) The interest rate in respect of the Senior Notes due 2006 will be
6.75% per annum (the "2006 Notes Interest Rate").

         (c) In the event that any date on which interest is payable on the
Senior Notes due 2006 is not a Business Day, then payment of interest payable on
such date will be made on the next succeeding day which is a Business Day, with
the same force and effect as if made on such date, and no interest shall accrue
on the amount so payable from the period from and after such Interest Payment
Date or Maturity Date, as the case may be (each date on which interest is
actually payable, an "Interest Payment Date").

         SECTION 2.4 Global Securities.

     The Senior Notes due 2006 shall be issued in the form of one or more Global
Securities in an aggregate principal amount equal to the aggregate principal
amount of all outstanding Senior Notes due 2006, to be registered in the name of
the U.S. Depositary, or its nominee, and delivered by the Trustee to or upon the
order of the U.S. Depositary for crediting to the accounts of its participants
pursuant to the written instructions of the Company. The Company upon any such
presentation shall execute one or more Global Securities in such aggregate
principal amount and deliver the same to the Trustee for authentication and
delivery in accordance with the Base Indenture and this Third Supplemental
Indenture. Payments on Senior Notes due 2006 issued as one or more Global
Securities will be made to the U.S. Depositary.

                                       5
<PAGE>   7

                                  ARTICLE III

                    REDEMPTION OF THE SENIOR NOTES DUE 2006

         SECTION 3.1 Optional Redemption of the Senior Notes due 2006.

         The Company at its option may, at any time, redeem the Senior Notes due
2006, in whole or in part, upon payment of a redemption price equal to (A) the
greater of (i) 100% of the principal amount of the Senior Notes due 2006 to be
redeemed and (ii) the Make Whole Amount, plus (B) accrued and unpaid interest,
if any, on the principal amount of Senior Notes due 2006 being redeemed to the
redemption date.

         SECTION 3.2 No Sinking Fund.

         The Senior Notes due 2006 are not entitled to the benefit of any
sinking fund.

                                   ARTICLE IV

                     REOPENING OF THE SENIOR NOTES DUE 2031

         SECTION 4.1 Reopening of the Senior Notes due 2031. The Senior Notes
due 2031 are hereby reopened and there is hereby authorized $160,000,000
principal amount of additional Senior Notes due 2031 (the "Additional 2031
Notes"), which shall rank equally in all respects with the Senior Notes due 2006
authorized by and issued under the Second Supplemental Indenture (the "Original
2031 Notes") in all respects, shall form a single series of $500,000,000
principal amount with the Original 2031 Notes, with the same CUSIP number, and
shall have the same terms as the Original 2031 Notes as set forth in the Second
Supplemental Indenture. Interest on the Additional 2031 Notes shall accrue from
April 5, 2001. The Additional 2031 Notes shall be in a form identical to the
form of the Original 2031 Notes except that the date of original issuance will
be July 16, 2001. The Additional 2031 Notes may be issued from time to time upon
written order of the Company to the Trustee for the authentication and delivery
of the Additional 2031 Notes pursuant to Section 2.2 of the Base Indenture. All
references to the Senior Notes due 2006 herein, in the Second Supplemental
Indenture and in any Senior Notes due 2006 shall be deemed to include the
Additional 2031 Notes issued hereunder.

                                       6
<PAGE>   8

                                    ARTICLE V

                             ORIGINAL ISSUE OF NOTES

         SECTION 5.1 Original Issue of Senior Notes due 2006.

         The Senior Notes due 2006 in the aggregate principal amount of
$340,000,000 may, upon execution of this Third Supplemental Indenture, be
executed by the Company and delivered to the Trustee for authentication, and the
Trustee shall thereupon authenticate and deliver said Notes to or upon the
written order of the Company pursuant to Section 2.2 of the Base Indenture
without any further action of the Company.

         SECTION 5.2 Original Issue of Senior Notes due 2031.

         The Additional 2031 Notes in the aggregate principal amount of
$160,000,000 may, upon execution of this Third Supplemental Indenture, be
executed by the Company and delivered to the Trustee for authentication, and the
Trustee shall thereupon authenticate and deliver said Notes to or upon the
written order of the Company pursuant to Section 2.2 of the Base Indenture
without any further action of the Company.

                                   ARTICLE VI

                                 MISCELLANEOUS

         SECTION 6.1 Ratification of Base Indenture, First Supplemental
Indenture and Second Supplemental Indenture.

         The Base Indenture, the First Supplemental Indenture and the Second
Supplemental Indenture, as supplemented by this Third Supplemental Indenture,
are in all respects ratified and confirmed, and this Third Supplemental
Indenture shall be deemed part of the Base Indenture in the manner and to the
extent herein and therein provided.

         SECTION 6.2 Trustee Not Responsible for Recitals.

         The recitals contained herein and in the Notes, except with respect to
the Trustee's certificates of authentication, shall be taken as the statements
of the Company, and the Trustee assumes no responsibility for the correctness of
the same.

                                       7
<PAGE>   9

The Trustee makes no representations as to the validity or sufficiency of this
Third Supplemental Indenture or of the Notes.

         SECTION 6.3 Governing Law.

         THIS THIRD SUPPLEMENTAL INDENTURE AND EACH NOTE OF EACH SERIES CREATED
HEREUNDER SHALL, PURSUANT TO SECTION 5-1401 OF THE NEW YORK GENERAL OBLIGATIONS
LAW, BE GOVERNED BY THE LAW OF THE STATE OF NEW YORK, WITHOUT REFERENCE TO THE
CHOICE OF LAW PROVISIONS THEREOF (OTHER THAN SUCH SECTION 5-1401).

         SECTION 6.4 Separability.

         In case any one or more of the provisions contained in this Third
Supplemental Indenture or in the Notes shall for any reason be held to be
invalid, illegal or unenforceable in any respect, such invalidity, illegality or
unenforceability shall not affect any other provisions of this Third
Supplemental Indenture or of the Notes, but this Third Supplemental Indenture
and the Notes shall be construed as if such invalid or illegal or unenforceable
provision had never been contained herein or therein.

         SECTION 6.5 Counterparts.

         This Third Supplemental Indenture may be executed in any number of
counterparts, each of which when so executed shall be deemed to be an original,
but all such counterparts shall together constitute but one and the same
instrument.

                                       8
<PAGE>   10

         IN WITNESS WHEREOF, the parties have caused this Third Supple-mental
Indenture to be duly executed by their respective officers thereunto duly
authorized as of the date first above written.

                                   NRG ENERGY, INC.

                                   By:
                                      ------------------------------------------
                                      Name:
                                      Title:

                                   THE BANK OF NEW
                                   YORK, as Trustee By: Name: Title:

                                   By:
                                      ------------------------------------------
                                      Name:
                                      Title:

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