SOUTHWESTERN PUBLIC SERVICE COMPANY

                                       TO

                            WILMINGTON TRUST COMPANY,
                                   AS TRUSTEE

                              --------------------

                          FIRST SUPPLEMENTAL INDENTURE

                          Dated as of October 21, 1996

                                       TO

                                    INDENTURE

                          Dated as of October 21, 1996

                              ---------------------


                     7.85% Deferrable Interest Subordinated
                          Debentures, Series A Due 2036

















<PAGE>


            FIRST SUPPLEMENTAL INDENTURE, dated as of October 21, 1996 (the
"First Supplemental Indenture"), between Southwestern Public Service Company, a
New Mexico corporation (the "Company"), and Wilmington Trust Company, as trustee
(the "Trustee") under the Indenture, dated as of October 21, 1996, from the
Company to the Trustee (the "Indenture") (terms used but not defined herein are
used as defined in the Indenture).

            WHEREAS, the Company has executed and delivered the Indenture to the
Trustee in order to provide for the future issuance of its subordinated
debentures (the "Securities"), such Securities to be issued from time to time in
one or more series as may be determined by the Company under the Indenture, in
an unlimited aggregate principal amount that may be authenticated and delivered
thereunder as provided in the Indenture;

            WHEREAS, Southwestern Public Service Capital I (the "Series A
Trust") may, pursuant to the Underwriting Agreement dated October 16, 1996 among
the Company, the Series A Trust and the Underwriters named therein, issue
$100,000,000 aggregate liquidation preference of its 7.85% Trust Preferred
Securities, Series A (the "Series A Preferred Securities") with a liquidation
amount of $25 per Series A Preferred Security;

            WHEREAS, the Company is guaranteeing (the "Parent Guarantee") the
payment of distributions on the Series A Preferred Securities, the payment of
the Redemption Price and the payment on liquidation with respect to the Series A
Preferred Securities, to the extent provided in the Guarantee Agreement, of even
date herewith between the Company and Wilmington Trust Company, as guarantee
trustee for the benefit of the holders of the Series A Preferred Securities;

            WHEREAS, the Company wishes to sell to the Series A Trust, and the
Series A Trust wishes to purchase from the Company, Series A Securities (as
defined below) in an aggregate principal amount equal to $103,092,775, and in
satisfaction of the purchase price for such Series A Securities, the
administrative trustees of the Series A Trust, on behalf of the Series A Trust,
wish to (i) execute and deliver to the Company Common Securities certificates
evidencing an ownership interest in the Series A Trust, registered in the name
of the Company, having an aggregate liquidation amount of $3,092,775 and (ii)
deliver to the Company the sum of $100,000,000;

            WHEREAS, the Company has duly authorized the creation of an issue of
its 7.85% Deferrable Interest Subordinated Debentures, Series A Due 2036 (the
"Series A Securities"), of the tenor and amount hereinafter set forth, and to
provide therefor the Company has duly authorized the execution and delivery of
this First Supplemental Indenture; and






<PAGE>


                                    -2-




            WHEREAS, all things necessary to make the Securities, when executed
by the Company and authenticated and delivered hereunder and duly issued by the
Company, the valid obligations of the Company, and to make this First
Supplemental Indenture a valid agreement of the Company, each in accordance with
their terms, have been done.

            NOW, THEREFORE, THIS FIRST SUPPLEMENTAL INDENTURE
WITNESSETH:

            For and in consideration of the premises and the purchase of the
Series A Securities by the Holders thereof, it is mutually agreed, for the equal
and proportionate benefit of all Holders of the Series A Securities as follows:


                                   ARTICLE ONE

                 GENERAL TERMS OF THE SERIES A SECURITIES

SECTION 101.  Title; Stated Maturity; Interest.

            The aggregate principal amount of Securities which may be
authenticated and delivered under this First Supplemental Indenture is limited
to $103,092,775 except for Securities authenticated and delivered upon
registration of transfer of, or in exchange for, or in lieu of, other Securities
pursuant to Section 303, 304, 305, 306, 906 or 1207 of the Indenture.

            The Securities shall be known and designated as the "7.85%
Deferrable Interest Subordinated Debentures, Series A due 2036" of the Company.
Their Stated Maturity shall be September 1, 2036, and they shall bear interest
at the rate of 7.85% per annum, from October 21, 1996 or from the most recent
Interest Payment Date to which interest has been paid or duly provided for, as
the case may be, payable quarterly (subject to deferral as set forth herein), in
arrears, on March 1, June 1, September 1 and December 1 of each year, commencing
December 1, 1996 until the principal thereof is paid or made available for
payment. Additional Interest Attributable to Deferral will compound quarterly
and will accrue at the rate of 7.85% per annum on any interest installment in
arrears for more than one quarter or during an extension of an interest payment
period as set forth below. In the event that any date on which interest is
payable on the Securities is not a Business Day, then a payment of the interest
payable on such date will be made on the next succeeding day which is a Business
Day except that, if




<PAGE>


                                    -3-



such Business Day is in the next succeeding calendar year, such
Interest Payment Date shall be the immediately preceding Business Day (and
without any interest or other payment in respect of any such delay).

            The Company shall have the right, at any time while any Series A
Securities are outstanding, from time to time to extend the interest payment
period thereon for up to 20 consecutive quarters (the "Extension Period") during
which period interest will compound quarterly and the Company shall have the
right to make partial payments of interest on any Interest Payment Date, and at
the end of which Extension Period the Company shall pay all interest then
accrued and unpaid thereon (together with Additional Interest Attributable to
Deferral at the rate specified for the Series A Securities to the extent
permitted by applicable law); provided that the Company shall not defer the
interest payment period with respect to Additional Interest Attributable to
Taxes and shall make payment thereof on the relevant Interest Payment Date;
provided further that during any such Extension Period, the Company shall not
declare or pay any dividends or distributions (other than dividends or
distributions in capital stock of the Company or other securities, including
other securities ranking junior in right of payment to the Series A Securities)
on, or redeem, purchase, acquire or make a liquidation payment with respect to,
any of its capital stock or any security ranking pari passu with or junior in
right of payment to the Series A Securities, or make any guarantee payment with
respect to the foregoing (other than pro rata payments under the Parent
Guarantee and any similar Parent Guarantees issued by the Company on behalf of
the holders of Preferred Securities issued by any issuer holding Securities) or
repurchase, or cause any of its Subsidiaries to repurchase, any security of the
Company ranking pari passu with or junior in right of payment to the Series A
Securities (except for payments made on any series of Securities upon the stated
maturity of such Securities); provided that the Company may redeem, purchase,
acquire or make a liquidation payment with respect to any of its capital stock
or any security ranking pari passu with or junior in right of payment to the
Series A Securities, make any guarantee payment with respect to the foregoing or
repurchase, or cause any of its subsidiaries to repurchase, any security of the
Company ranking pari passu with or junior in right of payment to the Series A
Securities with securities (or the proceeds from the issuance of securities)
having no higher ranking than the capital stock or the other securities which
are to be redeemed, purchased, or acquired, with respect to which a liquidation
payment is to be made, to




<PAGE>


                                    -4-



which a guarantee payment is to be made with respect to the foregoing or which
are to be repurchased. Prior to the termination of any such Extension Period,
the Company may further extend the interest payment period, provided that such
Extension Period together with all such previous and further extensions thereof
shall not exceed 20 consecutive quarters or extend beyond the Stated Maturity or
the Redemption Date of the Series A Securities. Upon the termination of any
Extension Period and upon the payment of all accrued and unpaid interest and any
Additional Interest then due, the Company may select a new Extension Period,
subject to the foregoing requirements. Except for Additional Interest
Attributable to Taxes, no interest shall be due and payable during an Extension
Period, except at the end thereof. The Company shall give the Series A Trust,
the Administrative Trustees of the Series A Trust and the Trustee notice of its
selection of such Extension Period, subject to the above requirements, at least
one Business Day prior to the earlier of (i) the related Interest Payment Date
or (ii) the date the Series A Trust is required to give notice to the New York
Stock Exchange or other applicable self-regulatory organization or to Holders of
the Series A Preferred Securities of the record date or the date such
distributions are payable, but in any event not less than one Business Day prior
to such record date. The Trustee shall promptly notify the Holders of the Series
A Preferred Securities and the Administrative Trustees of the Series A Trust of
the Company's selection of such an Extension Period.

            The principal of and interest on the Series A Securities shall be
payable at the office or agency of the Company in the United States maintained
for such purpose and at any other office or agency maintained by the Company for
such purpose in such coin or currency of the United States of America as at the
time of payment is legal tender for payment of public and private debts;
provided, however, that, at the option of the Company, payment of interest may
be made (i) by check mailed to the address of the Person entitled thereto as
such address shall appear in the Securities Register or (ii) by wire transfer in
immediately available funds at such place and to such account as may be
designated by the Person entitled thereto as specified in the Securities
Register; provided further, that for so long as any Series A Security is
registered in the name of the Property Trustee, payment of principal (including
Redemption Price and interest) shall be made by wire transfer in immediately
available funds at such place and to such account as may be designated by the
Property Trustee.






<PAGE>


                                    -5-



            The Series A Securities shall be subordinated in right of payment to
Senior Indebtedness as provided in Article Eleven of the Indenture. The Series A
Securities shall be pari passu with the Parent Guarantee.

            The Series A Securities shall be redeemable as provided in Section
102 below and in Article Twelve of the Indenture.

SECTION 102.  Redemption.

            At any time on or after October 21, 2001, the Company shall have the
right to redeem the Series A Securities, in whole or in part, from time to time,
at a Redemption Price equal to 100% of the principal amount of Series A
Securities to be redeemed plus accrued but unpaid interest, including any
Additional Interest, if any, to the Redemption Date.

            If a Tax Event or an Investment Company Act Event shall occur and be
continuing or upon the event of the termination or liquidation of the Series A
Trust pursuant to an order for the dissolution, termination, or liquidation of
the Series A Trust entered by a court of competent jurisdiction, the Company
shall have the right to redeem the Series A Securities in whole but not in part,
at a Redemption Price equal to 100% of the principal amount thereof plus accrued
but unpaid interest, including Additional Interest, if any, to the Redemption
Date.

            For so long as the Series A Trust is the Holder of all Series A
Securities Outstanding, the proceeds of any redemption described in this Section
102 shall be used by the Series A Trust to redeem Series A Preferred Securities
in accordance with their terms. The Company shall not redeem the Series A
Securities in part unless all accrued and unpaid interest (including any
Additional Interest) has been paid in full on all Series A Securities
Outstanding for all quarterly interest periods terminating on or prior to the
Redemption Date.

SECTION 103.  Global Security.

            If the Series A Trust is not the sole Holder of the Series A
Securities, in order to utilize a book-entry-only system for all or any portion
of the Series A Securities, all or a portion of the Series A Securities may be
issued in the form of one or more fully-registered Global Securities for the







<PAGE>


                                    -6-



aggregate principal amount of such Series A Securities (the "Series A Global
Securities"), which Series A Global Securities shall be registered in the name
of the Depositary selected by the Company or in the name of such Depositary's
nominee. The initial Depositary shall be The Depository Trust Company. Each
Series A Global Security shall be delivered by the Trustee to the Depositary or
pursuant to the Depositary's instruction.

            If an event described under Clause (2) of Section 305 of the
Indenture shall occur, then this Section 103 shall no longer be applicable to
the Series A Global Securities, and the Company will execute, and the Trustee
will authenticate and deliver (subject to receipt of an Officer's Certificate
evidencing the Company's determination if the Company has exercised its rights
under Clause (2)(C) of Section 305), Series A Securities in definitive
registered form without coupons, in authorized denominations, and in an
aggregate principal amount equal to the principal amount of the Series A Global
Securities in exchange for such Series A Global Securities. Upon the exchange of
Series A Global Securities for such Series A Securities in definitive registered
form, the Series A Global Securities shall be cancelled by the Trustee. Such
Series A Securities in definitive registered form issued in exchange for Series
A Global Securities pursuant to this Section 103 shall be registered in such
names and in such authorized denominations as the Depositary, pursuant to
instructions from its Direct or Indirect Participants or otherwise, shall
direct. The Trustee shall deliver such Series A Securities to the Persons in
whose names such Series A Securities are so registered.

            Except as provided below, owners solely of beneficial interests in a
Series A Global Security shall not be entitled to receive physical delivery of
Series A Securities in definitive form and will not be considered the Holders
thereof for any purpose under the Indenture.

            Members of or participants in the Depositary shall have no rights
under this Supplemental Indenture or the Indenture with respect to any Series A
Global Security held on their behalf by the Depositary, and such Depositary or
its nominee, as the case may be, may be treated by the Company, the Trustee, and
any agent of the Company or the Trustee as the Holder of such Series A Global
Security for all purposes whatsoever. Notwithstanding the foregoing, nothing
contained herein shall prevent the Company, the Trustee, or any agent of the
Company or the Trustee, from giving effect to any written certification, proxy
or other authorization furnished by the Depositary




<PAGE>


                                    -7-



or impair, as between the Depositary and its members or participants, the
operation of customary practices governing the exercise of the rights of a
Holder of any Series A Security, including without limitation the granting of
proxies or other authorization of participants to give or take any request,
demand, authorization, direction, notice, consent, waiver or other action which
a Holder is entitled to give or take under the Indenture.


                                   ARTICLE TWO

                            FORM OF SERIES A SECURITY

            The Series A Securities are to be in substantially the following
form:

                       [FORM OF FACE OF SERIES A SECURITY]

                       SOUTHWESTERN PUBLIC SERVICE COMPANY

                       % Deferrable Interest Subordinated
                          Debenture, Series A, due 2036

No. A-___________
$
 ----------------


            SOUTHWESTERN PUBLIC SERVICE COMPANY, a corporation duly organized
and existing under the laws of the State of New Mexico (herein called the
"Company," which term includes any successor corporation under the Indenture
hereinafter referred to), for value received, hereby promises to pay to
________________, or registered assigns, the principal sum of ________ DOLLARS
($________) on September 1, 2036 and to pay interest on said principal sum from
October 21, 1996 or from the most recent interest payment date (each such date,
an "Interest Payment Date") to which interest has been paid or duly provided
for, quarterly (subject to deferral as set forth herein) in arrears on March 1,
June 1, September 1 and December 1 of each year, commencing December 1, 1996, at
the rate of 7.85% per annum plus Additional Interest, if any, until the
principal hereof shall have become due and payable, and on any overdue
principal. The amount of interest payable for any period will be computed on the
basis of twelve 30-day months and a 360-day year and, for any period shorter
than a full monthly period, shall be computed on the basis of the actual




<PAGE>


                                    -8-



number of days elapsed in such period. In the event that any date on which
interest is payable on this Security is not a Business Day, then a payment of
the interest payable on such date will be made on the next succeeding day which
is a Business Day (and without any interest or other payment in respect of any
such delay), except that, if such Business Day is in the next succeeding
calendar year, such payment shall be made on the immediately preceding Business
Day, in each case with the same force and effect as if made on the date the
payment was originally payable. A "Business Day" shall mean any day other than a
Saturday or a Sunday or a day on which banking institutions in the City of New
York are authorized or required by law or executive order to remain closed or a
day on which the Corporate Trust Office of the Trustee, the principal office of
the property trustee under the Trust Agreement or the principal office of the
Company is closed for business. The interest installment so payable, and
punctually paid or duly provided for, on any Interest Payment Date will, as
provided in the Indenture, be paid to the Person in whose name this Security (or
one or more Predecessor Securities, as defined in the Indenture) is registered
at the close of business on the Regular Record Date for such interest
installment, which shall be the close of business on the Business Day next
preceding such Interest Payment Date or, if this Security is issued in
certificated form, the close of business on the 15th day next preceding such
Interest Payment Date. Any such interest installment not so punctually paid or
duly provided for shall forthwith cease to be payable to the Holder on such
Regular Record Date and may either be paid to the Person in whose name this
Security (or one or more Predecessor Securities) is registered at the close of
business on a Special Record Date for the payment of such Defaulted Interest to
be fixed by the Trustee, notice whereof shall be given to Holders of Securities
not less than 10 days prior to such Special Record Date, or be paid at any time
in any other lawful manner not inconsistent with the requirements of any
securities exchange on which the Securities may be listed, and upon such notice
as may be required by such exchange, all as more fully provided in said
Indenture.

            The Company shall have the right at any time during the term of this
Security, from time to time, to extend the interest payment period of such
Security for up to 20 consecutive quarters (an "Extension Period"), during which
period interest will compound quarterly and the Company shall have the right to
make partial payments of interest on any Interest Payment Date, and at the end
of which Extension Period the Company shall pay all interest then accrued and
unpaid (together with



<PAGE>


                                    -9-



Additional Interest thereon to the extent that payment of such interest is
permitted by applicable law); provided that the Company shall not defer the
interest payment period with respect to Additional Interest Attributable to
Taxes; provided further that during any such Extension Period, the Company shall
not declare or pay any dividends or distributions (other than dividends or
distributions in capital stock of the Company or other securities ranking junior
in right of payment to the Securities) on, or redeem, purchase, acquire or make
a liquidation payment with respect to, any of its capital stock or any security
ranking pari passu with or junior in right of payment to this Security, or make
any guarantee payment with respect to the foregoing (other than pro rata
payments under the Parent Guarantee and any similar Parent Guarantees issued by
the Company on behalf of the holders of Preferred Securities issued by any
issuer holding Securities) or repurchase, or cause any of its Subsidiaries to
repurchase, any security of the Company ranking pari passu with or junior in
right of payment to this Security (except for payments made on any series of
securities upon the stated maturity of such securities); provided that the
Company may redeem, purchase, acquire or make a liquidation payment with respect
to any of its capital stock or any security ranking pari passu with or junior in
right of payment to this Security, make any guarantee payment with respect to
the foregoing or repurchase, or cause any of its subsidiaries to repurchase, any
security of the Company ranking pari passu with or junior in right of payment to
this Security with securities (or the proceeds from the issuance of securities)
having no higher ranking than the capital stock or the other securities which
are to be redeemed, purchased, or acquired, with respect to which a liquidation
payment is to be made, to which a guarantee payment is to be made with respect
to the foregoing or which are to be repurchased. Prior to the termination of any
such Extension Period, the Company may further extend the interest payment
period, provided that such Extension Period together with all such previous and
further extensions thereof shall not exceed 20 consecutive quarters or extend
beyond the maturity of this Security. Upon the termination of any such Extension
Period and upon the payment of all accrued and unpaid interest and any
Additional Interest then due, the Company may select a new Extension Period,
subject to the foregoing requirements. No interest shall be due and payable
during an Extension Period except at the end thereof. The Company shall give the
Holder of this Security and the Trustee notice of its selection of an Extension
Period at least one Business Day prior to the earlier of (i) the Interest
Payment Date or (ii) the date the Series A Trust is required to give notice to




<PAGE>


                                   -10-



the New York Stock Exchange or other applicable self-regulatory organization or
to holders of the Series A Preferred Securities of the record date or the date
such distributions are payable, but in any event not less than one Business Day
prior to such record date.

            Payment of the principal of and interest on this Security will be
made at the office or agency of the Company maintained for that purpose in
Wilmington, Delaware, in such coin or currency of the United States of America
as at the time of payment is legal tender for payment of public and private
debts; provided, however, that at the option of the Company payment of interest
may be made (i) by check mailed to the address of the Person entitled thereto as
such address shall appear in the Securities Register or (ii) by wire transfer in
immediately available funds at such place and to such account as may be
designated by the Person entitled thereto as specified in the Securities
Register.

            The indebtedness evidenced by this Security is, to the extent
provided in the Indenture, subordinate and subject in right of payment to the
prior payment in full of all Senior Indebtedness, and this Security is issued
subject to the provisions of the Indenture with respect thereto. Each Holder of
this Security, by accepting the same, (a) agrees to and shall be bound by such
provisions, (b) authorizes and directs the Trustee on such Holder's behalf to
take such action as may be necessary or appropriate to effectuate the
subordination so provided and (c) appoints the Trustee such Holder's
attorney-in-fact for any and all such purposes. Each Holder hereof, by such
Holder's acceptance hereof, waives all notice of the acceptance of the
subordination provisions contained herein and in the Indenture of each holder of
Senior Indebtedness, whether now outstanding or hereafter incurred, and waives
reliance by each such Holder upon said provisions.

            Reference is hereby made to the further provisions of the Indenture
summarized on the reverse hereof, which further provisions shall for all
purposes have the same effect as if set forth at this place.

            Unless the certificate of authentication hereon has been executed by
the Trustee referred to on the reverse hereof by manual signature, this Security
shall not be entitled to any benefit under the Indenture or be valid or
obligatory for any purpose.







<PAGE>


                                   -11-



            IN WITNESS WHEREOF, the Company has caused this instrument to be
duly executed under its corporate seal.

Dated:  ________, 199

                                    SOUTHWESTERN PUBLIC SERVICE
                                     COMPANY


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


------------------------



                   FORM OF REVERSE OF SERIES A SECURITY

            This Security is one of a duly authorized issue of Securities of the
Company, designated as its 7.85% Deferrable Interest Subordinated Debentures,
Series A, due 2036 (therein called the "Securities"), limited in aggregate
principal amount to $103,092,775 issued under an Indenture, dated as of October
21, 1996 supplemented by a First Supplemental Indenture, dated as of October 21,
1996 (herein called the "Indenture"), between the Company and Wilmington Trust
Company, as Trustee (herein called the "Trustee", which term includes any
successor trustee under the Indenture), to which Indenture and such supplemental
indentures reference is hereby made for a statement of the respective rights,
limitations of rights, duties and immunities thereunder of the Trustee, the
Company and the Holders of the Securities, and of the terms upon which the
Securities are, and are to be, authenticated and delivered.

            All terms used in this Security which are defined in the Indenture
shall have the meanings assigned to them in the Indenture.

            At any time on or after October 21, 2001, the Company shall have the
right, subject to the terms and conditions of Article Twelve of the Indenture,
to redeem this Security at the option of the Company, without premium or
penalty, in whole or in part, at a Redemption Price equal to 100% of the
principal amount to be redeemed plus accrued but unpaid interest, 






<PAGE>


                                   -12-



including Additional Interest, if any, to the Redemption Date. If a Tax Event or
an Investment Company Event (as defined in the Indenture) shall occur and be
continuing, the Company shall have the right, subject to the terms and
conditions of Article Twelve of the Indenture, to redeem this Security at the
option of the Company, without premium or penalty, in whole but not in part, at
a Redemption Price equal to 100% of the principal amount thereof plus accrued
but unpaid interest, including Additional Interest, if any, to the Redemption
Date. Any redemption pursuant to this paragraph will be made upon not less than
30 nor more than 90 days' notice, at the Redemption Price. If the Securities are
only partially redeemed by the Company, the Securities will be redeemed pro
rata, by lot or in such other manner as the Trustee shall deem appropriate and
fair in its discretion and that may provide for the selection of a portion or
portions (equal to twenty-five U.S. dollars ($25) or any integral multiple
thereof) of the principal amount of any Security.

            In the event of the redemption of this Security in part only, a new
Security or Securities for the unredeemed portion hereof will be issued in the
name of the Holder hereof upon the cancellation hereof.

            If an Event of Default with respect to the Securities shall occur
and be continuing, the principal of the Securities may be declared due and
payable in the manner, with the effect and subject to the conditions provided in
the Indenture.

            The Indenture contains provisions for satisfaction and discharge at
any time of the entire indebtedness of this Security upon compliance by the
Company with certain conditions set forth in the Indenture.

            The Indenture contains provisions permitting the Company and the
Trustee, with the consent of Holders of the Securities of each series to be
affected of not less than a majority in principal amount of the Outstanding
Securities of such series, to modify the Indenture in a manner affecting the
rights of the Holders of the Securities of such series; provided that no such
modification may, without the consent of the Holder of each Outstanding Security
affected thereby, (i) extend the fixed maturity of the Securities, or reduce the
principal amount thereof, or reduce the rate or extend the time of payment of
interest (other than pursuant to an Extension Period) thereon, or reduce any
premium payable upon the redemption thereof, or (ii) reduce the percentage of
principal amount




<PAGE>


                                   -13-



of the Securities, the Holders of which are required to consent to any such
modification of the Indenture. The Indenture also contains provisions permitting
Holders of specified percentages in principal amount of the Securities of each
series at the time Outstanding, on behalf of the Holders of all Securities of
such series, to waive compliance by the Company with certain provisions of the
Indenture and certain past defaults under the Indenture and their consequences.
Any such consent or waiver by the Holder of this Security shall be conclusive
and binding upon such Holder and upon all future Holders of this Security and of
any Security issued upon the registration of transfer hereof or in exchange
herefor or in lieu hereof, whether or not notation of such consent or waiver is
made upon this Security.

            No reference herein to the Indenture and no provision of this
Security or of the Indenture shall alter or impair the obligation of the
Company, which is absolute and unconditional, to pay the principal of and
interest on this Security at the times, place and rate, and in the coin or
currency, herein prescribed.

            As provided in the Indenture and subject to certain limitations
therein set forth, the transfer of this Security is registrable in the
Securities Register, upon surrender of this Security for registration of
transfer at the office or agency of the Company, Wilmington Trust Company, 1100
North Market Street, Wilmington, Delaware 19890, duly endorsed by, or
accompanied by a written instrument of transfer in form satisfactory to the
Company and the Securities Registrar duly executed by, the Holder hereof or the
Holder's attorney thereunto duly authorized in writing, and thereupon one or
more new Securities, of authorized denominations and for the same aggregate
principal amount, will be issued to the designated transferee or transferees. No
service charge shall be made for any such registration of transfer or exchange,
but the Company may require payment of a sum sufficient to cover any tax or
other governmental charge payable in connection therewith.

            Prior to due presentment of this Security for registration of
transfer, the Company, the Trustee and any agent of the Company or the Trustee
may treat the Person in whose name this Security is registered as the owner
hereof for all purposes, whether or not this Security shall be overdue, and none
of the Company, the Trustee or any such agent shall be affected by notice to the
contrary.







<PAGE>


                                   -14-



            The Securities are issuable only in registered form without coupons
in denominations of $25 and any integral multiple thereof. As provided in the
Indenture and subject to certain limitations therein set forth, Securities are
exchangeable for a like aggregate principal amount of Securities of a different
authorized denomination, as requested by the Holder surrendering the same.

            A director, officer, employee or stockholder, as such, of the
Company shall not have any liability for any obligations of the Company under
the Securities or the Indenture or for any claim based on, in respect of or by
reason of such obligations or their creation. Each holder by accepting a
Security waives and releases all such liability. The waiver and release are part
of the consideration for the issuance of the Securities.

            THIS INDENTURE AND THE SECURITIES SHALL BE GOVERNED BY AND CONSTRUED
IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK WITHOUT REGARD TO
PRINCIPLES OF CONFLICTS OF LAW.


                                  ARTICLE THREE

                         MISCELLANEOUS PROVISIONS

            SECTION 301.  Definitions of Terms.

            Except as otherwise expressly provided in this First Supplemental
Indenture or in the form of Series A Security otherwise clearly required by the
context hereof or thereof, all terms used herein that are defined in the
Indenture shall have the meanings assigned to them therein.

            SECTION 302.  Ratification of Indenture.

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

            SECTION 303.  Recitals.

            The recitals herein contained are made by the Company and not by the
Trustee, and the Trustee assumes no responsibility for the correctness thereof.
The Trustee makes no 






<PAGE>


                                   -15-



representation as to the validity or sufficiency of this First Supplemental
Indenture.

            SECTION 304.  Counterparts.

            This First Supplemental Indenture may be executed in any number of
counterparts each of which shall be an original, but such counterparts shall
together constitute but one and the same instrument.






























<PAGE>


                                   -16-



            IN WITNESS WHEREOF, the parties hereto have caused this First
Supplemental Indenture to be duly executed, and their respective corporate seals
to be hereunto affixed and attested, on the date or dates indicated in the
acknowledgments and as of the day and year first above written.

                                    SOUTHWESTERN PUBLIC SERVICE
                                     COMPANY


                                    By /s/ Bill D. Helton
                                       ----------------------------
                                        Name:   Bill D. Helton
                                        Title:Chairman of the Board

Attest:


/s/ Mary Pullum
--------------------------
Name:  Mary Pullum
Title: Assistant Secretary

                                    WILMINGTON TRUST COMPANY,
                                      as Trustee


                                    By /s/ Donald G. MacKelcan
                                       --------------------------
                                        Name: Donald G. MacKelcan
                                        Title:Assistant Vice
                                                President

Attest:


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