<PAGE>
 
                                                                   EXHIBIT 10.13

                                FIRST AMENDMENT
                                      To
                    WHITTAKER CORPORATION CREDIT AGREEMENT

                          Dated as of April 21, 1995

     This FIRST AMENDMENT (this "Amendment") is among WHITTAKER CORPORATION, a 
Delaware corporation (the "Borrower"), the Financial Institutions party to the 
Credit Agreement referred to below (the "Lenders"), and NATIONSBANK OF TEXAS, 
N.A., as agent (the "Agent") for the Lenders thereunder.

                            PRELIMINARY STATEMENTS:

     (1) The Borrower, the Lenders and the Agent have entered into a Credit 
Agreement dated as of January 23, 1995 (the "Credit Agreement"; capitalized 
terms used and not otherwise defined herein have the meanings assigned to such 
terms in the Credit Agreement).

     (2) In connection with the proposed acquisition (the "HLS Acquisition") by 
the Borrower of 100% of the capital stock of Hughes LAN Systems, Inc., a 
California corporation ("HLS"), from Hughes Aircraft Company, a Delaware 
corporation (the "Seller"), the Borrower has requested that the Agent and the 
Lenders agree to certain amendments to the terms of the Credit Agreement.

     (3) The Agent and the Lenders are, on the terms and conditions stated 
below, willing to grant the requests of the Borrower.

     NOW, THEREFORE, in consideration of the premises and for other good and 
valuable consideration, the receipt and sufficiency of which are hereby 
acknowledged, the parties hereto hereby agree as follows:

          SECTION 1. Amendments to Credit Agreement. The Credit Agreement is, 
effective concurrently with and only upon the consummation of the HLS 
Acquisition and subject to the satisfaction of the conditions precedent set 
forth in Section 3 hereof, hereby amended as follows:

          (a) Section 1.01 of the Credit Agreement is hereby amended by adding 
     thereto, in appropriate alphabetical order, the following defined terms:

              "'First Amendment' means the First Amendment dated as of April 21,
          1995 among the Borrower, the Lenders and the Agent.
 
              "'HLS' means Hughes LAN Systems, Inc., a California corporation.

              "'HLS Acquisition' means the acquisition by the Borrower of 100% 
          of the capital stock of HLS.

              "'HLS Acquisition Agreement' means the Stock Purchase Agreement 
          dated as of March 23, 1995 by and between the Seller and the Borrower.
<PAGE>
 
          "'HLS Acquisition Documents' means the HLS Acquisition Agreement, 
     the HLS Subordinated Debt Documents and each other document, instrument and
     agreement executed and/or delivered in connection with the HLS Acquisition.

          "'HLS Contingent Payments' means (i) "Contingent Payments" as defined
     in Exhibit 1.3(c) to the HLS Acquisition Agreement, (ii) HLS Mandatory
     Payments, and (iii) any other amounts payable by the Borrower or any of its
     Subsidiaries to the Seller or any of its Affiliates based on the revenues
     or income of HLS; provided, however, that any amounts required to be paid
     as a result of adjustments, pursuant to Section 1.6 of the HLS Acquisition
     Agreement, to the purchase price payable in connection with the HLS
     Acquisition shall not constitute HLS Contingent Payments.

          "'HLS Mandatory Payments' means mandatory payments under Section 2.2 
     of Exhibit 1.3(c) to the HLS Acquisiiton Agreement.

          "'HLS Subordinated Debt' means the 7% convertible Subordinated Debt in
     the original principal amount of $15,000,000 incurred by the Borrower in 
     connection with the HLS Acquisition.
       
          "'HLS Subordinated Debt Documents' means (i) the HLS Subordinated
     Note, and (ii) any other instruments and agreements evidencing and
     governing the HLS Subordinated Debt.

          "'HLS Subordinated Note' means the 7% Convertible Subordinated Note 
     due May 1, 2005 in the original principal amount of $15,000,000 and any
     note or notes issued in exchange therefor or replacement thereof so long as
     each such note is in substantially the form of Exhibit 1.3(b) to the HLS
     Acquisition Agreement.

          "'HLS Transaction Documents' means the HLS Acquisition Documents and 
     the First Amendment.

          "'Seller' means Hughes Aircraft Company, a Delaware corporation.

          "'Specified Bermite Land proceeds' means the cash proceeds from the 
     sale, transfer, lease (other than the existing lease with the City of Santa
     Clarita and any other lease with a term, including all extension options,
     of two years or less) or other disposition of all or any portion of the
     Bermite Land (including any sale or other disposition of any Securities of
     or any other equity interest in any Affiliate of the Borrower with any
     ownership interest in the Bermite Land) to any Person other than the
     Borrower or a wholly owned Subsidiary of the Borrower, net of (a) all
     reasonable costs incurred and payable within twelve months of, and as a
     result of, the applicable transaction by the Borrower or any of its
     Subsidiaries to a Person that is not its Affiliate, (b) the amount (as
     estimated by the Borrower in good faith) of income, franchise, transfer or
     other taxes payable by the Borrower in cash within 12 months as a result of
     such transaction (after giving effect to all deductions, credits and other
     items which reduce tax liability and, at the time of determination, are
     available or reasonably anticipated to be available), and (c) amounts
     payable to Northholme Partners or its successors in connection with the
     applicable transaction pursuant to the terms of the Bermite

                                       2

<PAGE>
 
          Development Agreement, in each case to the extent, but only to the
          extent, that the amounts so deducted are, at the time of receipt of
          the applicable cash proceeds, paid or payable to a Person that is not
          its Affiliate and are properly attributable to the transaction."

          (b) The definition of "Fixed Charge Coverage Ratio" contained in 
     Section 1.01 of the Credit Agreement is herby amended and restated in its 
     entirety to read as follows:

              "'Fixed Charge Coverage Ratio' means, subject to Section 6.01(o), 
          for any period, the quotient obtained by dividing (a) Consolidated
          EBITDA of the Borrower and its Subsidiaries for such period minus the
          sum of (i) Consolidated Capital Expenditures of the Borrower and its
          Subsidiaries in such period and (ii) the amount of any HLS Contingent
          Payments accrued in such period by (b) the sum of Consolidated
          Interest Expense for such period plus scheduled payments of the
          principal amount of (i) the Term Advances required to be made during
          such period in accordance with the provisions of Section 2.03(a) (as
          such scheduled payments may be reduced by any prepayments of the Term
          Advances) and (ii) any other funded debt or other indebtedness for
          borrowed money (including Capitalized Leases) of the Borrower and its
          Subsidiaries (determined in accordance with GAAP but excluding any
          Revolving Advances and L/C Advances) required to be made during such
          period."

          (c) Section 1.01 of the Credit Agreement is hereby amended by adding, 
     immediately prior to the period at the end of the definition of the term
     "Debt", a proviso to read as follows:

          "; provided, however, that HLS Contingent Payments shall not 
     constitute 'Debt' hereunder".

          (d) Section 2.05(b) of the Credit Agreement is hereby amended by 
     adding thereto a new subsection (iii) to read as follows:

              "(iii) Mandatory Prepayment: Specified Bermite Land Proceeds. On 
the first Business Day after any Specified Bermite Land Proceeds are received by
the Borrower or any of its Subsidiaries, the Borrower shall pay to each Lender 
(in accordance with the provisions of Section 2.09(a)) such Lender's Pro Rata 
Share of an amount equal to such Specified Bermite Land Proceeds, to be applied 
to the prepayment of each scheduled principal installment of the Term Advances 
(ratably in accordance with the respective principal amounts of each such 
installment), until the Term Advances are repaid in full."

          (e) Section 6.01 of the Credit Agreement is hereby amended by adding 
     thereto a new subsection (h) to read as follows:

          "(h) Delivery of HLS Transaction Documents. The Borrower shall deliver
      to the Agent as soon as reasonably practicable after the closing of the
      HLS Acquisition, and in any event within 30 days of such closing, copies
      of the HLS Acquisition Agreement, the HLS Subordinated Debt Documents and
      each other HLS Acquisition Document reasonably requested by the Agent or
      the Required Lenders, each certified as of the date delivered as being
      true, correct and complete."

                                       3
<PAGE>
 
     (f) Section 6.02(f)(v) of the Credit Agreement is hereby amended and 
restated in its entirety to read as follows:

          "(v) from and after the date which is twelve months after the closing
     date of the HLS Acquisition, Operating Investments (in addition to
     Investments otherwise expressly permitted hereunder) so long as no Default
     has occurred and is continuing or would occur as a result of the
     consummation thereof and so long as:

              (A) the amount of each such Investment (or series of related
        Investments) does not exceed 10% of the total assets of the Borrower
        and its Subsidiaries (determined on a Consolidated basis in accordance
        with GAAP at the time of such Investment); and

              (B) the cumulative amount of all Operating Investments made
        during any period of twelve consecutive months, whether or not 
        outstanding or recovered, does not exceed $10,000,000;".

     (g) Section 6.02(f) of the Credit Agreement is hereby further amended by
(i) deleting the word "and" which immediately follows the semi-colon at the
end of subsection (viii) of such Section, (ii) replacing the period at the end
of subsection (ix) of such Section with "; and", and (iii) adding to such
Section a new subsection (x) to read as follows:
 
          "(x) the HLS Acquisition, but only if (i) such acquisition is
     consummated (A) on substantially the terms disclosed in writing to the
     Lenders by the Borrower prior to execution of the First Amendment, and
     (B) in accordance with the terms and conditions of the HLS Acquisition
     Agreement (without any material modification from the form delivered to
     the Lenders prior to their execution of the First Amendment) without any
     material modification or amendment thereof or waiver thereunder which has
     not been approved by the Required Lenders, and (ii) the purchase price
     payable in connection with such acquisition does not exceed $17,500,000
     plus the amount of any positive adjustment of such amount pursuant to
     Section 1.6 of the HLS Acquisition Agreement, plus amounts payable in
     respect of the HLS Subordinated Note (as if effect on the closing date of
     the HLS Acquisition) and HLS Contingent Payments."

     (h) Section 6.02 of the Credit Agreement is hereby further amended by
adding thereto a new subsection (o) to read as follows:

          "(o) HLS Contingent Payments, Etc. Make or permit to be made any
     payment in respect of any HLS Contingent Payment if, at the time of such
     payment, the Fixed Charge Coverage Ratio (determined as set forth below
     in the case of any HLS Mandatory Payment) for the period of the four most
     recently ended fiscal quarters of the Borrower is less than 1.50 to 1.0,
     or prepay prior to the scheduled maturity thereof in any manner any HLS
     Contingent Payments, or amend, modify or change in any manner Section 2.6
     of Exhibit 1.3(c) to the HLS Acquisition Agreement or any other term or
     provision of the HLS Acquisition Documents if such amendment, 
     modification or change would increase the amount of, or accelerate the 
     date for payment of, any HLS Contingent Payment. For purposes of 
     determining the amount of any HLS Mandatory  Payment which may be made
     at any time (and only for such purposes), the term "Fixed Charge

                                      4  


<PAGE>
 
     Coverage Ratio" means, the quotient obtained by dividing (a) Consolidated
     EBITDA of the Borrower and its Subsidiaries for such period minus the sum
     of (i) Consolidated Capital Expenditures of the Borrower and its
     Subsidiaries in such period, and (ii) the amount of any HLS Contingent
     Payments accrued in such period, and (iii) without duplication of any
     amount included under the foregoing clause (ii), the amount of any HLS
     Mandatory Payments made in such period and any HLS Mandatory Payments
     proposed to be made in the next subsequent fiscal quarter, plus the amount
     of any cash proceeds received by the Borrower or any of its Subsidiaries in
     such period (and, without duplication, in the next subsequent fiscal
     quarter) in connection with any sale of any capital stock or assets of HLS
     which constitutes a "Trigger Event" as defined in Exhibit 1.3(c) to the HLS
     Acquisition Agreement (net of all taxes and expenses incurred by the
     Borrower in connection with such sale, in each case as determined by the
     Borrower in good faith) by (b) the sum of Consolidated Interest Expense for
     such period plus scheduled payments of the principal amount of (i) the Term
     Advances required to be made during such period in accordance with the
     provisions of Section 2.03(a) (as such scheduled payments may be reduced by
     any prepayments of the Term Advances) and (ii) any other funded debt or
     other indebtedness for borrowed money (including Capitalized Leases) of
     the Borrower and its Subsidiaries (determined in accordance with GAAP but
     excluding any Revolving Advances and L/C Advances) required to be made
     during such period. Prior to make any HLS Mandatory Payment, the Borrower
     shall deliver to the Agent an Officers' Certificate of the Borrower setting
     forth the amount of such HLS Mandatory Payment and the calculation of the
     Fixed Charge Coverage Ratio (as set forth in this Section 6.02(o)) for the
     period of the four most recently ended fiscal quarters of the Borrower
     after giving effect to such HLS Mandatory Payment."

     (i) Section 6.04(b) of the Credit Agreement is hereby amended and restated 
in its entirety to read as follows:

          "(b) Leverage Ratio. Maintain at all times during the period of twelve
     consecutive months immediately following the closing date of the HLS 
     Acquisition a ratio of Consolidated Total Debt to Consolidated Total
     Capitalization of not greater than 0.55 to 1.0 and maintain at all other
     times a ratio of Consolidated Total Debt to Consolidated Total 
     Capitalization of not greater than 0.50 to 1.0."

     (j) Section 6.04(d) of the Credit Agreement is hereby amended and restated 
in its entirety to read as follows:

          "(d) Consolidated Tangible Net Worth. Maintain a Consolidated Tangible
     Net Worth, as determined as of the last day of each fiscal quarter, of 
     not less than the sum of (i) 50% of cumulative Consolidated Net Income 
     for all fiscal quarters commencing with and including the fiscal quarter 
     ending July 31, 1995 (but excluding Consolidated Net Income for any 
     fiscal quarter for which Consolidated Net Income is a negative number), 
     (ii) 75% of the amount of HLS Subordinated Debt, if any, converted to 
     any equity interest in the Borrower or any of its Subsidiaries, and
     (iii) $50,000,000."

                                       5
<PAGE>
 
     (k) Article IX of the Credit Agreement is hereby amended by adding thereto
a new Section 9.19 to read as follows:

          "SECTION 9.19. Notices Under HLS Acquisition Agreement. If, at any
     time, the Borrower shall fail to maintain for any period of four 
     consecutive fiscal quarters ending on the last day of any fiscal quarter
     a Fixed Charge Coverage Ratio equal to or greater than 1.50 to 1.0, then,
     at the request of the Agent, the Borrower shall, and the Agent is hereby
     authorized to, give written notice to the Seller pursuant to the terms of
     the HLS Acquisition Agreement that a 'Fixed Charge Deficiency' has occurred
     and is continuing; provided that, if the Agent gives any such notice, the 
     Agent shall deliver a copy thereof to the Borrower concurrently with the 
     delivery of such notice to the Seller (it being understood and agreed 
     that the failure by the Agent to so deliver such a copy to the Borrower
     shall not affect the effectiveness of any such notice and shall not 
     result in any liability on the part of the Agent). The Borrower agrees 
     that, unless the Agent has made a request therefor pursuant to this 
     Section 9.19, the Borrower will not deliver any notice under the HLS 
     Acquisition Agreement of the occurrence of a 'Fixed Charge Deficiency' 
     without the prior written consent of the Agent."

     SECTION 2. Consent to HLS Subordinated Debt. Upon the effectiveness of this
Amendment, the Agent and the Lenders hereby approve the HLS Subordinated Note 
(without any material modification from the form delivered to the Lenders prior 
to their execution hereof) for the purposes of the definition of "Subordinated 
Debt" contained in Section 1.01 of the Credit Agreement.

     SECTION 3. Conditions to Effectiveness. This Amendment shall become 
effective when:

          (a) the Agent has executed this Amendment and has received 
     counterparts of this Amendment executed by the Borrower and the Required 
     Lenders or, as to any of the Lenders, advice satisfactory to the Agent 
     that such Lender has executed this Amendment;

          (b) the Agent has received counterparts of the Consent appended hereto
     executed by each of the Guarantors and Grantors listed therein (such 
     Guarantors and Grantors, together with the Borrower, collectively the 
     "Loan Parties");

          (c) the Borrower shall have paid to the Agent on or prior to the date 
     of execution by the Borrower of this Amendment, in accordance with Section 
     2.09(a) of the Credit Agreement, for the account of the Lenders, an 
     amendment fee in an amount equal to 0.25% of the sum of the outstanding 
     Term Advances, the outstanding Revolving Advances, the outstanding Letter
     of Credit Obligations and the Unused Revolving Commitments of the Lenders;

          (d) the Borrower shall have taken such steps, and shall have executed 
     and/or delivered such certificates, instruments and other documents, if 
     any, as the Agent may reasonably require to ensure that the certificates 
     representing 100% of the capital stock of HLS shall be pledged to the 
     Agent pursuant to the Security Agreement simultaneously with the closing
     of the HLS Acquisition and shall be delivered to the Agent substantially 
     concurrently therewith; and

          (e) the Agent has received a certificate, dated as of the date of 
     closing of the HLS Acquisition (the "HLS Acquisition Closing Date") and 
     in form and substance satisfactory to the

                                       6
<PAGE>
 
     Agent, of the Borrower and each other Loan Party, signed on behalf of the
     Borrower and such other Loan Party by its President or its Vice President
     and its Secretary or any Assistant Secretary, certifying as to (A) the due
     incorporation and good standing of the Borrower and each other Loan Party,
     as a corporation organized under the laws of the state of its
     incorporation, and the absence of any proceeding for the dissolution or
     liquidation of the Borrower or such other Loan Party, (B) the truth, both
     immediately prior to consummation of the HLS Acquisition and after giving
     effect thereto, of the representations and warranties contained in this
     Amendment and in each of the Loan Documents as though made on and as of the
     date thereof (other than any such representations or warranties that, by
     their terms, specifically refer to a date other than the HLS Acquisition
     Closing Date), (C) the absence, both immediately prior to consummation of
     the HLS Acquisition and after giving effect thereto, of any event occurring
     and continuing that constitutes a Default, and (D) the names and true
     signatures of the officers of the Borrower or such other Loan Party
     authorized to sign this Amendment or the consent hereto, as applicable.

     SECTION 4. Representations and Warranties. The Borrower represents and
                ------------------------------
warrants as follows:

          (a)  Authority; Enforceability. The Borrower and each of its
               -------------------------
     Subsidiaries has the requisite corporate power and authority (i) to
     execute, deliver and perform each HLS Transaction Document executed or to
     be executed by it, and (ii) to file the HLS Transaction Documents filed by
     it, or to be filed by it, with each appropriate Governmental Authority. The
     execution, delivery and performance (or filing, as the case may be) by the
     Borrower and each of its Subsidiaries of each HLS Transaction Document to
     which it is or is to be a party and the consummation of the transactions
     contemplated thereby, have been duly approved by the Board of Directors of
     such Person and no other corporate proceedings on the part of such Person
     are necessary to consummate such transactions. Each HLS Transaction
     Document to which the Borrower or any of its Subsidiaries is a party has
     been duly executed and delivered by the Borrower and/or such Subsidiary, as
     the case may be, and constitutes each such Person's legal, valid and
     binding obligation, enforceable against such Person in accordance with its
     terms, and is in full force and effect.

          (b)  No Conflict. The execution, delivery and performance by the 
               -----------
     Borrower and each of its Subsidiaries of each HLS Transaction Document to
     which it is party and the consummation of the transactions contemplated
     thereby do not and will not (i) constitute a tortious interference with any
     Contractual Obligation of the Borrower or any of its Subsidiaries to any
     Person, or (ii) conflict with or violate such Person's certificate or
     articles of incorporation or bylaws, or other organizational documents, as
     the case may be, or (iii) conflict with, result in a breach of or
     constitute (with or without notice or lapse of time or both) a default
     under any material Requirement of Law or material Contractual Obligation of
     the Borrower or any of its Subsidiaries, or require termination of any
     material Contractual Obligation of any such Person, or (iv) result in or
     require the creation or imposition of any Lien whatsoever upon any of the
     properties or assets of the Borrower or any of its Subsidiaries (other than
     Liens in favor of the Agent arising pursuant to the Loan Documents or Liens
     permitted pursuant to Section 6.02(a)) of the Credit Agreement, or (v)
     require any approval of stockholders or any approval or consent of any
     Person under any Contractual Obligation of any Loan Party, except for
     corporate authorizations described in Section 3(a) which have been obtained
     and are in full force and effect on the HLS Acquisition Closing Date.

                                       7
<PAGE>
 
           (c) Governmental Consents. The execution, delivery and performance by
               ---------------------
     the Borrower and each of its Subsidiaries of each HLS Transaction Document
     to which it is a party and the consummation of the transactions
     contemplated thereby do not and will not require any registration with,
     consent or approval of, or notice to, or other action to, with or by any
     Governmental Authority, except for filings (i) required pursuant to the
     Hart-Scott-Rodino Antitrust Improvement Act of 1976 (all of which have been
     made), (ii) with the Securities and Exchange Commission under the
     Securities Exchange Act, and (iii) to perfect the Liens created by the
     Collateral Documents which, in the case of the foregoing clauses (ii) and
     (iii), have been, or will in due course prior to the time required, be
     made. Any waiting period under the Hart-Scott-Rodino Antitrust Improvement
     Act of 1976 applicable to the consummation of the transactions contemplated
     by the HLS Transaction Documents has, or as of the HLS Acquisition Closing
     Date shall have, expired.

     Section 5. Reference to and Effect on the Loan Documents. (a) Upon and 
                ---------------------------------------------
after the effectiveness of this Amendment, each reference in the Credit 
Agreement to "this Agreement", "hereunder", "hereof" or words of like import 
referring to the Credit Agreement, and each reference in the other Loan 
Documents to "the Credit Agreement", "thereunder", "thereof" or words of like 
import referring to the Credit Agreement, shall mean and be a reference to the 
Credit Agreement as modified and amended hereby.

     (b) Except as specifically amended above, the Credit Agreement and all 
other Loan Documents, are and shall continue to be in full force and effect and 
are hereby in all respects ratified and confirmed. Without limiting the 
generality of the foregoing, the Collateral Documents and all of the Collateral 
described therein do and shall continue to secure the payment of all Secured 
Obligations under and as defined therein, in each case as amended hereby.

     (c) The execution, delivery and effectiveness of this Amendment shall not, 
except as expressly provided herein, operate as a waiver of any right, power or 
remedy of any Lender or the Agent under any of the Loan Documents, nor 
constitute a waiver of any provision of any of the Loan Documents.

     Section 6. Costs, Expenses and Taxes. The Borrower agrees to pay on demand 
                -------------------------
to the Agent, all costs and expenses of the Agent in connection with the 
preparation, execution, delivery and administration of this Amendment and the 
other instruments and documents to be delivered hereunder, including, without 
limitation, the reasonable fees and out-of-pocket expenses of counsel for the 
Agent with respect thereto and with respect to advising the Agent as to its 
rights and responsibilities hereunder and thereunder. The Borrower further 
agrees to pay on demand all costs and expenses, if any (including, without 
limitation, reasonable counsel fees and expenses), in connection with the 
enforcement (whether through negotiations, legal proceedings or otherwise) of 
this Amendment and the other instruments and documents to be delivered 
hereunder, including, without limitation, reasonable counsel fees and expenses 
in connection with the enforcement of rights under this Section 6. In addition, 
the Borrower shall pay any and all stamp and other taxes (excluding, in the case
                                                          ---------
of each Lender, net income taxes that are imposed by the United States and 
franchise taxes and income taxes that are imposed on such Lender by the state or
foreign jurisdiction under the laws of which such Lender is organized or any
political subdivision thereof or therein, and franchise taxes based on income
and income taxes that are imposed on such Lender by any jurisdiction or any
political subdivision thereof or therein in which is located such Lender's
Applicable Lending Office or principal office), and fees, payable or determined
to be payable in connection with the execution, delivery and filing of this
Amendment and the other instruments and

                                       8
<PAGE>
 
documents, if any, to be delivered hereunder, and agrees to save the Agent and 
each Lender harmless from and against any and all liabilities with respect to or
resulting from any delay in paying or omission to pay such taxes or fees.

     SECTION 7.  Execution in Counterparts.  This Amendment may be executed in
                 -------------------------
any number of counterparts and by different parties hereto in separate 
counterparts, each of which when so executed and delivered shall be deemed to be
an original and all of which taken together shall constitute but one and the 
same agreement. Delivery of an executed counterpart of a signature page to this 
Amendment or the Consent hereto by telefacsimile shall be effective as delivery 
of a manually executed counterpart of this Amendment or such Consent.

     SECTION 8.  Governing Law.  This Amendment shall be governed by, and
                 -------------
construed in accordance with, the laws of the State of New York.

                           [Signature Pages Follow]

                                       9
<PAGE>
 
     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be 
executed by their respective officers thereunto duly authorized, as of the date 
first above written.
 

                                       WHITTAKER CORPORATION,
                                       a Delaware corporation

                                       By: /s/ JOHN K. OTTO
                                           --------------------------------
                                           John K. Otto
                                           Treasurer



                                       NATIONSBANK OF TEXAS, N.A.,
                                       as Agent

                                       By: /s/ ANDREA P. COLLIAS
                                           -------------------------------- 
                                           Andrea P. Collias
                                           Vice President

                                      10
<PAGE>
 
                                       Lenders:
                                       -------

                                       NATIONSBANK OF TEXAS, N.A.


                                       By: /s/ ANDREA P. COLLIAS
                                           -----------------------------
                                           Andrea P. Collias
                                           Vice President

                                       BANK OF AMERICA NATIONAL TRUST AND
                                       SAVINGS ASSOCIATION

                                      
                                       By: /s/ LORI KANNEGIETER
                                           -----------------------------
                                           Title: Vice President


                                       THE BANK OF CALIFORNIA, N.A.

                                      
                                       By: /s/ J. DEREK WATSON
                                           -----------------------------
                                           Title: Corporate Banking Officer


                                       CITY NATIONAL BANK

                                      
                                       By: /s/ ERICH BOLLINGER
                                           -----------------------------
                                           Title: Vice President


                                       KREDIETBANK N.V.

                                      
                                       By: /s/ DIANE GRIMMIG
                                           -----------------------------
                                           Title: Vice President

                                      
                                       By: /s/ ROBERT SNAUFFER
                                           -----------------------------
                                           Title: Vice President


                                       SANWA BANK CALIFORNIA

                                      
                                       By: /s/ JOE ARCO
                                           -----------------------------
                                           Title: Vice President


                                       UNION BANK

                                      
                                       By: /s/ ROBERT C. PETERSEN
                                           -----------------------------
                                           Title:

                                      11
<PAGE>
 
                                    CONSENT

                          Dated as of April 21, 1995

    The undersigned, as Guarantors under the "Guaranty" and as Grantors under 
the "Security Agreement" (as such terms are defined in and under the Credit 
Agreement referred to in the foregoing First Amendment), each hereby consents 
and agrees to the said First Amendment and hereby confirms and agrees that (i) 
the Guaranty and Security Agreement are, and shall continue to be, in full force
and effect and are hereby ratified and confirmed in all respects except that, 
upon the effectiveness of, and on and after the date of, the said First 
Amendment, each reference in the Guaranty and the Security Agreement to the 
Credit Agreement, "thereunder", "thereof" or words of like import referring to 
the Credit Agreement, shall mean and be a reference to the Credit Agreement as 
amended by the said First Amendment and (ii) the Security Agreement and all of 
the Collateral described therein do, and shall continue to, secure the payment 
of all of the Secured Obligations as defined therein.

                   BLUE BELL LEASE, INC., a California corporation, 
                   METROPOLITAN FINANCIAL SERVICES CORPORATION, a Colorado
                   corporation, PARK CHEMICAL COMPANY, a Michigan corporation,
                   WHITTAKER CONTROLS, INC., a California corporation,
                   WHITTAKER CORP., a Maine corporation, WHITTAKER ORDNANCE, 
                   INC., a Delaware corporation, WHITTAKER PORTA BELLA
                   DEVELOPMENT, INC., a California corporation, WHITTAKER 
                   SERVICES CORPORATION, a California corporation, WHITTAKER
                   TECHNICAL PRODUCTS, INC., a Colorado corporation, and 
                   WHITTAKER DEVELOPMENT CO., a Delaware corporation



                   By:  /s/ JOHN K. OTTO
                       -------------------------------------
                       John K. Otto
                       Treasurer of each of the foregoing Loan Parties

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