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                                                                   EXHIBIT 10.20


                           NINTH AMENDMENT AND WAIVER
                            TO WHITTAKER CORPORATION
                     AMENDED AND RESTATED CREDIT AGREEMENT
                         DATED AS OF DECEMBER 31, 1997


          This NINTH AMENDMENT AND WAIVER (the "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, CIBC Inc., as co-agent, and the Agent
entered into an Amended and Restated Credit Agreement dated as of April 10, 1996
(as amended to date, the "Credit Agreement"; capitalized terms used and not
otherwise defined herein have the meanings assigned to such terms in the Credit
Agreement).

          2.  The Borrower has requested that the Lenders, among other things,
waive, during the period starting on and including December 31, 1997 to (but not
including) January 31, 1998 (the "Waiver Period"), any Default arising as a
result of non-compliance with Section 6.04(a), (b), (c) or (d) of the Credit
Agreement.

          3.  The Lenders are, on the terms and conditions stated below, willing
to grant the request 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.  Effective as of the date
                      ------------------------------                           
hereof and subject to the satisfaction of the conditions precedent set forth in
Section 4 hereof, the Credit Agreement is hereby amended as follows:

          (a) During the Waiver Period, the definition of "Applicable Margin" is
     amended and restated in its entirety as follows:

              "APPLICABLE MARGIN" means 4.25% per annum.
               -----------------                        

          (b) During the Waiver Period, the third sentence of Section 2.01(b) of
     the Credit Agreement is hereby amended and restated in its entirety as
     follows:

               "Each Revolving Borrowing shall be in an aggregate amount of
          $500,000 or an integral multiple of $500,000 in excess thereof unless
          such Revolving Borrowing is in the amount of the aggregate Unused
          Revolving Commitment of each Revolving Lender and shall consist of
          Revolving Advances made by the Revolving Lenders ratably according to
          their respective Revolving Commitments."
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          (c) During the Waiver Period, the proviso of Section 2.05(a) is hereby
     amended to read as follows:

               "provided, however, that each partial prepayment of Revolving
          Advances shall be in the aggregate principal amount of $500,000 or any
          multiple of $500,000 in excess thereof."

          (d) During the Waiver Period, notwithstanding anything to the contrary
     in the Credit Agreement, the aggregate outstanding amount of Revolving
     Advances plus Letter of Credit Obligations shall not exceed $83,000,000.

          (e) During the Waiver Period, Section 3.05(a) of the Credit Agreement
     is hereby amended and restated in its entirety as follows:

               "SECTION 3.05. LETTER OF CREDIT COMPENSATION.
                              ----------------------------- 

                    (a) The Borrower shall pay to the Agent:

                         (i) for the account of the Issuing Bank which Issues a
               Letter of Credit, an issuance fee in an amount equal to 1/8 of 1%
               per annum of the average daily Available Amount of such Letter of
               Credit outstanding from time to time; and

                         (ii) for the account of each Revolving Lender, a letter
               of credit fee with respect to each Letter of Credit, in each case
               in an amount equal to

                              (A) with respect to each Financial Standby Letter
                    of Credit, a percentage per annum equal to the Applicable
                    Margin plus 1%, times the amount of such Lender's Revolving
                    Pro Rata Share of the average daily Available Amount of such
                    Letter of Credit outstanding from time to time;

                              (B) with respect to each Performance Standby
                    Letter of Credit, a percentage per annum equal to the
                    Applicable Margin plus 1/2%, times the amount of such
                    Lender's Revolving Pro Rata Share of the average daily
                    Available Amount of such Letter of Credit outstanding from
                    time to time; and

                              (C) with respect to each Commercial Letter of
                    Credit, 0.25% of the amount of such Lender's Revolving Pro
                    Rata Share of the Available Amount of such Letter of Credit
                    as of the date of Issuance thereof.

               The letter of credit and issuance fees payable under this Section
               3.05(a) shall be payable monthly on the last Business Day of each
               month, commencing December 31, 1997, and on the Revolving
               Commitment Termination Date except that the letter of credit fee
               payable under Section 3.05(a)(ii)(C) shall be payable upon
               issuance of the applicable Letter of Credit.  For purposes of
               computing any fees under this Section 3.05(a), the determination
               of the maximum amount

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               available to be drawn under a Letter of Credit at any time shall
               assume strict compliance with all conditions for drawing.  Any
               fees paid pursuant to this Section 3.05(a) are nonrefundable."

          SECTION 2.  WAIVER.  (a) Subject to the terms and conditions hereof,
                      ------                                                  
Lenders hereby waive, but only during the Waiver Period, the Specified Defaults
(hereinafter defined); provided, however, that Lenders' waiver of the Specified
                       --------  -------                                       
Defaults and their rights and remedies as a result of the occurrence thereof
shall not constitute and shall not be deemed to constitute a waiver of any other
Event of Default, whether arising as a result of further violations of any
provision of the Credit Agreement previously violated by the Borrower, or a
waiver of any rights and remedies arising as a result of such other Events of
Default.  As used herein, "Specified Defaults" shall mean the failure of the
                           ------------------                               
Borrower to comply with Sections 6.04(a), (b), (c) and (d) of the Credit
Agreement.  At the end of the Waiver Period, the waiver of the Specified
Defaults will automatically terminate.

     (b) In consideration of Lenders' waiver of the Specified Defaults and
certain other good and valuable consideration, the Borrower hereby expressly
acknowledges and agrees that neither it nor any Guarantor or Grantor has any
setoffs, counterclaims, adjustments, recoupments, defenses, claims or actions of
any character, whether contingent, non-contingent, liquidated, unliquidated,
fixed, matured, unmatured, disputed, undisputed, legal, equitable, secured or
unsecured, known or unknown, against any Lender or Agent or any grounds or cause
for reduction, modification or subordination of the Obligations under the Loan
Documents or any liens or security interests of any Lender or the Agent.  To the
extent the Borrower or any Guarantor or Grantor may possess any such setoffs,
counterclaims, adjustments, recoupments, claims, actions, grounds or causes, the
Borrower and each Guarantor and Grantor hereby waive, and hereby release each
Lender and Agent from, any and all such setoffs, counterclaims, adjustments,
recoupments, claims, actions, grounds and causes, such waiver and release being
with full knowledge and understanding of the circumstances and effects of such
waiver and release and after having consulted counsel with respect thereto.

          SECTION 3.  AMENDMENT AND WAIVER FEE.  In consideration of the
                      ------------------------                          
execution by and agreement to this Amendment by the Lenders, the Borrower shall
pay to the Agent for the account of each Lender such Lender's Revolving Pro Rata
Share of 1/4% of its Revolving Commitment outstanding on December 31, 1997, and
1/4% of its Term Advances outstanding on December 31, 1997.

          SECTION 4.  CONDITIONS TO EFFECTIVENESS.  This Amendment shall not be
                      ---------------------------                              
effective until all proceedings of the Borrower taken in connection herewith and
the transactions contemplated hereby shall be satisfactory in form and substance
to Agent and Required Lenders, and each of the following conditions precedent
shall have been satisfied:

          (a) The Agent has received counterparts of this Amendment executed by
     the Borrower and Required Lenders and counterparts of the Consent appended
     hereto (the "Consent") executed by each of the Guarantors and Grantors (as
     defined in the Security Agreement) listed therein (such Guarantors and
     Grantors, together with the Borrower, each a "Loan Party" and,
     collectively, the "Loan Parties");

          (b) The Agent shall have received for the account of the Lenders the
     fee described in Section 3 above.

          (c) All fees and expenses, including legal and other professional fees
     and expenses incurred, payable on or prior to the date of this Amendment to
     Agent, including, without

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     limitation, the fees and expenses of its counsel, shall have been paid to
     the extent that same had been billed prior to the date of this Amendment;
     and

          (d) Agent and each Lender shall have received each of the following:

               (1) a certificate of the Borrower certifying (i) as to the
          accuracy, after giving effect to this Amendment, of the
          representations and warranties set forth in Article V of the Credit
          Agreement, the other Loan Documents and in this Amendment, and (ii)
          that there exists no Default or Event of Default, after giving effect
          to this Amendment and the execution, delivery and performance of this
          Amendment will not cause a Default or Event of Default; and

               (2) such other documents, instruments, and certificates, as Agent
          or Required Lenders shall deem necessary or appropriate in connection
          with this Amendment and the transactions contemplated hereby,
          including without limitation copies of resolutions of the board of
          directors of the Borrower authorizing the transactions contemplated by
          this Amendment.

          SECTION 5.  REPRESENTATIONS AND WARRANTIES.  The Borrower represents
                      ------------------------------                          
and warrants as follows:

          (a) AUTHORITY.  The Borrower and each other Loan Party has the
              ---------                                                 
     requisite corporate power and authority to execute and deliver this
     Amendment or the Consent, as applicable, and to perform its obligations
     hereunder and under the Loan Documents (as modified hereby) to which it is
     a party.  The execution, delivery and performance by the Borrower of this
     Amendment and by each other Loan Party of the Consent, and the performance
     by each Loan Party of each Loan Document to which it is a party have been
     duly approved by all necessary corporate action of such Loan Party and no
     other corporate proceedings on the part of such Loan Party are necessary to
     consummate such transactions.

          (b) ENFORCEABILITY.  This Amendment has been duly executed and
              --------------                                            
     delivered by the Borrower.  The Consent has been duly executed and
     delivered by each Guarantor and Grantor.  This Amendment and each Loan
     Document (as modified hereby) is the legal, valid and binding obligation of
     each Loan Party hereto or thereto, enforceable against such Loan Party in
     accordance with its terms, and is in full force and effect.

          (c) REPRESENTATIONS AND WARRANTIES.  The representations and
              ------------------------------                          
     warranties contained in each Loan Document (other than any such
     representations or warranties that, by their terms, are specifically made
     as of a date other than the date hereof) are correct on and as of the date
     hereof as though made on and as of the date hereof.

          (d) NO DEFAULT.  After giving effect to this Amendment, no event has
              ----------                                                      
     occurred and is continuing that constitutes a Default or Event of Default.

          SECTION 6.  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 hereby.

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          (b) Except as specifically modified 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 an amendment of any right,
power or remedy of any Lender or the Agent under any of the Loan Documents, nor
constitute an amendment of any provision of any of the Loan Documents.

          SECTION 7.  FURTHER ASSURANCES.  The Borrower shall execute and
                      ------------------                                 
deliver such further agreements, documents, instruments, and certificates in
form and substance satisfactory to Agent, as Agent or any Lender may deem
necessary or appropriate in connection with this Amendment.

          SECTION 8.  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 by telefacsimile shall be effective as delivery of a
manually executed counterpart of this Amendment or such Consent.

          SECTION 9.  WAIVER OF JURY TRIAL.  TO THE MAXIMUM EXTENT PERMITTED BY
                      --------------------                                     
LAW, EACH OF THE BORROWER, THE AGENT AND THE LENDERS HEREBY IRREVOCABLY WAIVES
ANY RIGHT THAT IT MAY HAVE TO A TRIAL BY JURY OF ANY DISPUTE (WHETHER A CLAIM IN
TORT, CONTRACT, EQUITY, OR OTHERWISE) ARISING UNDER OR RELATING TO THIS
AGREEMENT, THE OTHER LOAN DOCUMENTS, OR ANY RELATED MATTERS, AND AGREES THAT ANY
SUCH DISPUTE SHALL BE TRIED BEFORE A JUDGE SITTING WITHOUT A JURY.

          SECTION 10.  GOVERNING LAW.  This Amendment shall be governed by, and
                       -------------                                           
construed in accordance with, the laws of the State of New York.


     [REMAINDER OF PAGE LEFT INTENTIONALLY BLANK.  SIGNATURE PAGES FOLLOW.]

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     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/ William E. Livingstone, IV
                                 ------------------------------------
                                    William E. Livingstone, IV
                                    Senior Vice President



                              Lenders:
                              ------- 

                              NATIONSBANK OF TEXAS, N.A.


                              By:/s/ William E. Livingstone, IV
                                 ------------------------------------
                                    William E. Livingstone, IV
                                    Senior Vice President


                              BT HOLDINGS (NEW YORK), INC.


                              By:/s/ Robert W. Hevner
                                 ------------------------------------
                                    Robert W. Hevner, Vice President


                              DK ACQUISITION PARTNERS, L.P.

                              By:   M.H. DAVIDSON & CO., its general partner


                              By:/s/ Michael J. Leffell
                                 ------------------------------------
                                  Michael J. Leffell, General Partner

                                       6
<PAGE>
 
                              GOLDMAN SACHS CREDIT PARTNERS L.P.


                              By:/s/ Edward C. Forst
                                 ------------------------------------------
                                 Edward C. Forst, Authorized Signatory


                              MERRILL LYNCH, PIERCE, FENNER, & SMITH
                              INCORPORATED


                              By:/s/ Neil Brisson
                                 ------------------------------------------
                                    Neil Brisson, Director


                              MERRILL LYNCH SENIOR FLOATING RATE
                              FUND, INC.


                              By:/s/ R. Douglas Henderson
                                 ------------------------------------------
                                 R. Douglas Henderson, Authorized Signatory


                              MERRILL LYNCH SENIOR HIGH INCOME
                              PORTFOLIO, INC.


                              By:/s/ R. Douglas Henderson
                                 ------------------------------------------
                                 R. Douglas Henderson, Authorized Signatory


                              MERRILL LYNCH DEBT STRATEGIES
                              PORTFOLIO

                              By:   MERRILL LYNCH ASSET
                                    MANAGEMENT, L.P., as Investment Advisor


                              By:/s/ R. Douglas Henderson
                                 ------------------------------------------
                                 R. Douglas Henderson, Authorized Signatory


                              CANPARTNERS INVESTMENTS IV, LLC


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

                                       7
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                                    CONSENT


     Each of the undersigned, as Guarantors under the "Guaranty" and as grantors
under the "Security Agreement" (as such terms are defined in the Credit
Agreement referred to in the foregoing Amendment), each hereby consents and
agrees to the foregoing Amendment and to be bound by the terms and provisions
thereof, and agrees that (i) the Guaranty and the 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 such Amendment each reference 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
such Amendment, and (ii) the collateral described in the Security Agreement
shall continue to secure the payment of the indebtedness therein described.



                         AVIANT INFORMATION, INC. (formerly BLUE BELL LEASE,
                         INC.), a California corporation, METROPOLITAN FINANCIAL
                         SERVICES CORPORATION, a Colorado corporation, PARK
                         CHEMICAL COMPANY, a Michigan corporation, WHITTAKER
                         COMMUNICATIONS, INC., a California 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, WHITTAKER DEVELOPMENT CO., a
                         Delaware corporation, WHITTAKER XYPLEX, INC., a
                         Delaware corporation, and XYPLEX, INC., a Massachusetts
                         corporation



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

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