<PAGE>   1
                                                            EXHIBIT 10.46

                         CORPORATE SERVICES AGREEMENT

      THIS CORPORATE SERVICES AGREEMENT (this "Agreement") dated as of December
15, 1999, is entered into by and between NRG Energy, Inc., a Delaware
Corporation (the "Provider"), and Montville Power LLC, a Delaware limited
liability company (the "Company").

                                   RECITALS

      1.    The Company has obtained the rights to acquire, own and operate the
Montville Generating Station (the"Facility") located in Montville, Connecticut.

      2.    The Company desires to employ the services of the Provider to assist
in its operation of the Facility and related business functions; and

      3.    The Provider agrees to provide various services to the Company in
support of the operations of the Facility as provided in this Agreement.

                                  AGREEMENT

      In consideration of the premises and the covenants, conditions, and
agreements contained herein, and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledge, the parties hereto
agree as follows:

                                  ARTICLE 1
                                 DEFINITIONS

      1.1   Definitions.  Whenever used in this Agreement with initial
capitalization, the following terms shall have the meanings specified or
referred to in this Article 1.

      "Affiliate" means, with respect to any person or entity, (i) each entity
that such person or entity Controls, (ii) each person or entity that Controls
such person or entity, and (iii) each entity that is under common Control with
such person or entity.

      "Agreement" shall have the meaning provided in the introductory paragraph
hereof.

      "Control" means the possession, directly or indirectly, through one or
more intermediaries, of (i) in the case of a corporation, a majority of the
outstanding voting securities thereof; (ii) in the case of a limited liability
company, partnership, limited partnership or venture, the right to more than 50%
of the distributions therefrom (including liquidating distributions); (iii) in
the case of a trust or estate, including a business trust, a majority of the
beneficial interest therein; and (iv) in the case of any other entity, a
majority of the economic or beneficial interest therein.

      "Effective Date" means the date of this Agreement.

      "Outsource" means to cause a Service to be provided by a third-party
provider which is not an Affiliate of the Provider.

      "Outsourced Services" shall means those Services which the Provider
Outsources to third-party providers which are not Affiliates of the Provider.

      "Services" means the performance of any work, direction of work, technical
or commercial information,


<PAGE>   2




data, consulting, staff augmentation or any other corporate business function
performed for or on behalf of the Company by the Provider in functional areas
such as but not limited to: human resources, accounting, finance, treasury, tax,
office administration, information technology, engineering, construction
management, environmental, legal and safety.

      1.2   Terminology.  Unless the context of this Agreement clearly requires
otherwise, (a) pronouns, wherever used herein, and of whatever gender, will
include natural persons and corporations and associations of every kind and
character, (b) the word "included" or "including" will mean "including without
limitation", (c) the word "or" will have the inclusive meaning represented by
the phrase "and/or", (d) the words "hereof," "herein," "hereunder," and similar
terms in this Agreement will refer to this Agreement as a whole and not any
particular section or article in which such words appear and (e) all terms
defined in this Agreement in the singular will have the same meaning when used
in the plural and vice versa. The section, article and other headings in this
Agreement are for reference purposed and will not control or affect the
construction of this Agreement or the interpretation hereof in any respect.
Article, section and subsection references are to his Agreement unless otherwise
specified.

                                  ARTICLE 2
                                   SERVICES

      2.01  General.  The Company hereby retains the Provider, and the Provider
accepts the obligation, to provide to the Company certain Services in accordance
with the terms of this Agreement. At the Provider's election, it may cause one
or more of its Affiliates or third-party contractors to provide the Services;
provided, however, that the Provider shall remain responsible for the provision
of the Services (including Outsourced Services) in accordance with the terms of
this Agreement.

      2.2   Services.  The Provider shall provide all Services to the Company on
an as-requested basis in support of the day-to-day business of the Company. The
Company shall use a letter, work order, purchase order or other official
document to authorize the performance of Services by Provider. Such document
shall state, as a minimum, the scope of Services to be performed, schedule
requirements, budget and a reference to this Agreement. The Provider shall
acknowledge requested Services in writing.

      2.3   Personnel.  The Provider shall provide as required by the Company
all technical, professional, supervisorial, managerial, administrative and other
personnel as are necessary to perform the Services. Such personnel shall be
qualified and experienced in the Services to which they are assigned. The
working hours, rates of compensation and all other matters relating to the
employment of individuals employed by the Provider or its Affiliates in the
performance of the Services shall be determined solely by the Provider or its
respective Affiliates.

      2.4   Standards for Performance of Services.  The Provider shall, and
shall cause its Affiliates and the providers of Outsourced Services to, perform
the Services with reasonable diligence and dispatch in a prudent, cost effective
and efficient manner, in accordance with all applicable laws, regulations,
codes, permits, licenses, and standards, and in accordance with the terms and
conditions of this Agreement. The Provider may determine in its sole discretion
whether or not to Outsource a Service.

      2.5   Right to Request Instruction.  At any time, the Provider may, if it
reasonably deems it to be necessary or appropriate, request written instructions
from the Company prior to the necessity for taking action with respect to any
matter contemplated by this Agreement, and may defer action thereon pending the
receipt of such written instructions.

                                  ARTICLE 3
                                   PAYMENT

      3.1   Payment.  The Company, in consideration for the performance of the
Services by the Provider, agrees to pay the Provider all pre-approved charges,
costs, expenses, taxes, fees and losses not compensated by insurance, which are
incurred by Provider in the performance of the Services hereunder. These
charges, costs, expenses, taxes, fees and losses shall include, but are not
limited to:

<PAGE>   3


            (a)   Charges for the time of all personnel employed by the Provider
      in the performance of the Services at the each person's standard
      intracompany labor rate as set forth by personnel category on Annex A
      hereto, which time charges include federal and state payroll taxes and
      insurance, Provider benefit programs, overhead and an arms-length,
      commercially reasonable mark-up. Such charges shall be subject to
      appropriate adjustment for any changes in payroll taxes or insurance, or
      changes in benefit programs.

            (b)   Transportation, travel, hotel and living expenses, including
      use of employees' personal cars at Provider's current standard rates. All
      reasonable moving, relocation, travel and living expenses incurred in
      connection with assignment of Provider's permanent personnel to a location
      other than Provider's permanent offices and from such location at the
      conclusion of assignment.

            (c)   Miscellaneous expenses, including but not limited to
      telegrams, telex, telefacsimile, telephone services, postage and similar
      miscellaneous items incurred in connection with the Services, all at
      Provider's current standard rates.

            (d)   Reproduction costs of all drawings, manuals, specifications,
      and other documents required for the Services; and costs for the use of
      computer, all at Provider's current standard rates or at actual cost to
      Provider if prepared by others.

            (e)   Cost of any permits, fees, licenses or royalties required.
      Costs of any sales, use or similar taxes or fees imposed by a federal,
      state, municipal or other government or agency thereof.

            (f)   Fees, costs, damages, or disbursements incurred in connection
      with any labor, patent, or commercial litigation or any third party claim,
      suit, or cause of action, arising out of or in connection with the
      performance of the Services by Provider (except disputes between Provider
      and the Company) or claims, suites or causes of action pursued on behalf
      of the Company by Provider.

            (g)   Premiums and brokerage fees on all bonds and insurance
      policies which may be required by Company in addition to those listed
      herein, and any loss under the deductible features of any insurance
      policies, whether furnished by Provider or Company.

      3.2   Invoicing.

            (a)   The Provider shall invoice the Company by the fifteenth (15th)
      day of each month for all Services performed with respect to the preceding
      month and any adjustments that may be necessary to correct prior invoices.
      All invoices shall reflect in reasonable detail a description of the
      Services performed during the preceding month and documentation available
      to the Provider backing up invoiced charges and shall be due and payable
      within thirty (30) days after its receipt. The Company shall pay all
      undisputed amounts on each invoice, but shall be entitled to withhold
      payment of any amount in dispute and shall notify the Provider within
      thirty (30) days from receipt of the invoice of the disputed amount and
      the reasons each such charge is disputed by the Company. The Provider
      shall promptly provide the Company with records relating to the disputed
      amount so as to enable the parties to resolve the dispute.

            (b)   Any statement or payment not disputed in writing by either
      party within two years of the date of such statement or payment shall be
      considered final and no longer subject to adjustment. The Company shall
      not be obligated to pay for any changes for which statements for payment
      are submitted more than two years after the termination of this Agreement.

                                  ARTICLE 4
                               LIMITED WARRANTY

      4.1   Warranty.  Provider warrants that the Services performed under this
Agreement will be in accordance with accepted professional standards and
practices existing as of the date that such Services are performed. The sole and
exclusive remedy for breach of this warranty shall be for Provider to re-perform
the portion of defective Services, written notice of which is promptly given by
Company to Provider within a period of one (1)


<PAGE>   4




year from the date that the defective Service was performed under this
Agreement. All costs of any re-performance shall be reimbursed by Company to
Provider but Provider shall receive no additional profit thereon.

      4.2   Disclaimer.  There are no warranties other than the above, either
express or implied, including without limitation any warranties of
merchantability or fitness for particular purpose applicable to Providers
services performed under this Agreement.

                                  ARTICLE 5
                           LIMITATION OF LIABILITY

      5.1   Limitation of Liability.  Whether due to delay, breach of contract
or warranty, tort (including without limitation negligence), or any other cause,
neither Provider nor its Affiliates or subcontractors shall be liable for any
special, indirect, punitive, or consequential damages of any nature, including
without limitation loss of actual or anticipated profits, revenues, or product,
loss by reason of shutdown, nonoperation, or increased expense of manufacturing
or operation, or any costs, labor, or materials required for reconstruction or
repairs. Provider's maximum liability under or arising out of this Agreement
shall in no event exceed the value of the Services performed during the calendar
year prior to the cause giving rise to or creating any such liability.

                                  ARTICLE 6
                   TERM AND TERMINATION; EVENTS OF DEFAULT

      6.01  Term.  The term of this Agreement shall commence on the Effective
Date and shall continue until terminated in writing by the Company.

      6.02  Events of Default.  If one or more of the following events occurs
with respect to a party hereto, it will constitute an "Event of Default" with
respect to such party:

            (a)   Failure to Perform Obligations.  Such party fails to perform
      or observe any material obligation under this agreement and such failure
      continues for more than thirty (30) days after the non-defaulting party
      has given notice thereof to such party (or if the nature of such default
      is such that it is not capable of being cured within thirty (30) days,
      then the failure of such party to commence to cure such default within
      thirty (30) days and to diligently and continuously pursue the cure of
      such default thereafter, but in no event may such extended cure period
      exceed one hundred eighty (180) days);

            (b)   Bankruptcy.  Such party becomes subject to a bankruptcy or is
      declared insolvent.

      6.03  Remedies; Exclusivity.  At any time during the continuance of an
Event of Default, the non-defaulting party will have the right to (a) elect, by
giving notice to the defaulting party, not to be bound in any respect by the
provisions of this Agreement during such continuance, in which case such party
will have no obligations or liabilities hereunder during such period, (b)
terminate the Agreement upon giving notice of termination to the defaulting
party. No failure on the part of either Provider, the Company to exercise and no
delay in exercising, and no course of dealing with respect to, any right, power
or privilege under this Agreement will operate as a waiver thereof, nor will any
single or partial exercise of any right, power or privilege under this Agreement
preclude any other or further exercise thereof.

                                  ARTICLE 7
                                MISCELLANEOUS

      7.1   Severability.  In the event any portion of this Agreement shall be
found by a court of competent jurisdiction to be unenforceable, that portion of
the Agreement will be null and void and the remainder of the Agreement will be
binding on the parties as if the unenforceable provisions had never been
contained herein. To the fullest extent permitted by Law, the remedies set forth
in this Section 6.3 are the exclusive remedies for a default


<PAGE>   5




hereunder; provided that with respect to (i) disputed or unpaid invoices
relating to services rendered prior to any termination and (ii) claims for
indemnity relating to events that occurred prior to any termination each party
shall also have all rights and remedies contemplated herein in Sections 7.10 and
7.11 or otherwise provided in Law or Equity.

      7.2   Assignment.  Except for the ability of the Provider to cause one or
more of the Services to be performed by one of its Affiliates or a third-party
provider, no party shall have the right to assign its rights or obligations
under this Agreement without the consent of the other party.

      7.3   Entire Agreement.  This Agreement constitutes the entire agreement
of the parties relating to the performance of the Services. All prior or
contemporaneous written or oral agreements are merged herein.

      7.4   Law.  This Agreement shall be subject to and governed by the laws of
the State of New York, excluding any conflicts-of-law rule or principle that
might refer the construction or interpretation of this Agreement to the laws of
another state.

      7.5   Amendment of Modification.  This Agreement may be amended or
modified from time to time only by a written amendment signed by the parties
hereto.

      7.6   Notices.  Any notice, request, instruction, correspondence or other
document to be given hereunder by either party to the other (herein collectively
called "Notice") shall be in writing and delivered personally or mailed, postage
prepaid, or by telegram or telecopier, as follows:

            (a)   if to the Company, to:

                  Montville Power LLC
                  c/o NRG Energy, Inc.
                  1221 Nicollet Mall, Suite 700
                  Minneapolis, MN  55403
                  Attention:  Vice President

            (b)   if to Provider, to:

                  NRG Energy, Inc.
                  1221 Nicollet Mall, Suite 700
                  Minneapolis, MN  55403
                  Attention:  Vice President of Corporate Operating Services

      7.7   Insurance.  The Company shall carry and keep in force, at all times,
Commercial General Liability insurance in such policy limits as are usual and
customary for its business and as it deems necessary to protect it from risks of
loss arising from the performance of Service under this Agreement. The Company
shall name the Provider as an additional insured on these policies and shall
indemnify Provider to the same extent. The Company waive all rights and any
subrogation rights such as it or its insurers may have against Provider its
vendors and subcontractors and their employees, agents, officers, directors, and
any of their affiliated or associated companies, for any losses or damages,
including without limitation all consequential damages resulting from any and
all risks and losses, however and whenever arising, from the Services performed
hereunder, or other risks covered under a Commercial General Liability insurance
policy.

      7.8   Prosecution of the Work; Force Majeure.  Provider shall
substantially perform the Services in accordance with a schedule mutually agreed
upon between the parties. Any completion dates specified are tentative only and
Provider shall have no liability to the Company for late completion. If the
prosecution of the Services is delayed or affected by any of the following force
majeure occurrences: acts or failures to act by the Company or any separate
contractors, engineers, vendors, or consultants employed by the Company or any
other party not in privity of this Agreement; acts of God or the elements; acts
or failures to act by government or any agency thereof; changes, inaccuracies,
incompleteness, or differences in site conditions or any data or information
supplied to the Provider; changes in laws or regulations; delays in permitting;
delays in receipt of engineering data or vendor drawings; fire;


<PAGE>   6




unusually sever weather, natural disasters, or unavoidable casualties; riot;
civil disorders; labor shortages or disputes; strikes, picketing, or arbitration
proceedings; delays in transportation, material, or equipment deliveries;
material, equipment, or fuel shortages; or any other causes beyond the
Provider's reasonable control, the schedule shall be extended for the period of
time attributable to such delay and all fixed elements of pricing, if any, shall
be equitably adjusted.

      7.9   No Third-Party Beneficiary.  The provisions of this Agreement are
enforceable solely by the parties to this Agreement, and no other person shall
have the right, separate and apart from the Company or the Provider, to enforce
any provision of this Agreement or to compel any party to this Agreement to
comply with the terms of this Agreement.

      7.10  Disputes.  The Provider and the Company agree to negotiate in good
faith in an effort to resolve any dispute related to this Agreement that may
arise between the parties. If the dispute cannot be resolved promptly by
negotiation, at a senior management level the either party may give the other
party written notice that the dispute should be submitted to mediation.
Promptly thereafter, a mutually acceptable mediator shall be chosen by the
parties. who shall share the cost of mediation services equally.  If the
dispute has not been resolved by mediation within ninety (90) days after the
date of written notice requesting mediation, then either party may initiate
litigation and pursue any and all remedies at law or at equity that such party
is entitled to.

      7.11  Indemnification.

      (a)   The Company agrees that it will indemnify and hold harmless the
Provider, its Affiliates and their respective directors, officers, employees,
and agents from and against any and all losses, claims, damages and
liabilities, joint or several, to which the Provider may become subject under
any applicable federal or state law, or otherwise, relating to or arising out
of the engagement of the Provider pursuant to, and the performance by the
Provider of the services contemplated by, this Agreement.  The Company will
reimburse the Provider for all costs and expenses (including reasonable counsel
fees and expenses) as they are incurred in connection with the investigation
of, preparation of or defense of any pending or threatened claim or any action
or proceeding covered by such indemnity.  The Company will not be liable under
the foregoing indemnification provisions to the extent that any loss, claim,
damage, liability or expense is found in a final judgment by a court to have
resulted primarily from the bad faith or gross negligence of the Provider or
the relevant Affiliate.

      (b)   The Provider agrees that it will indemnify and hold harmless the
Company and its directors, officers, employees, and agents from and against any
and all losses, claims, damages and liabilities, joint or several, to which the
Company  may become subject under any applicable federal or state law, or
otherwise, relating to or arising out of the willful misconduct or gross
negligence of the Provider or its Affiliates.  The Provider will reimburse the
Company for all costs and expenses (including reasonable counsel fees and
expenses) as they are incurred in connection with the investigation of,
preparation of or defense of any pending or threatened claim or any actions or
proceedings covered by such indemnity.  The Provider will not be liable under
the foregoing indemnification provisions to the extent that any loss, claim,
damage, liability or expense is found in a final judgment by a court to have
resulted primarily from the bad faith or gross negligence of the Company.

      7.12  The Company is Sole Beneficiary.  The Company acknowledges that the
Services shall be provided only with respect to the businesses of the Company.
The Company shall request performance of any Services for the benefit of any
entity other than the Company.


<PAGE>   7



      IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
signed on their behalf by their duly authorized officers.

                                    NRG ENERGY, INC.
<TABLE>
<S>                                <C>
                                    By: /s/David Peterson
                                        -----------------------------------------------------
                                       Name: David Peterson
                                            -------------------------------------------------
                                       Title: Chairman, President and Chief Executive Officer
                                            -------------------------------------------------



                                    MONTVILLE POWER LLC

                                    By: /s/ Craig A.Mataczynski
                                        -----------------------------------------------------
                                       Name: Craig A.Mataczynski
                                            -------------------------------------------------
                                       Title:President
                                            -------------------------------------------------
</TABLE>