EXHIBIT 4.15
SUBSIDIARIES OF FEDERAL DATA CORPORATION

                                         AMENDMENT
                                        -----------

                      AMENDMENT (this "Agreement"), dated as of October 22, 1999
  among FEDERAL DATA CORPORATION (the "Borrower"), the institutions party to the
  Credit Agreement referred to below (the "Banks") and BANKERS TRUST COMPANY, as
  Agent (the  "Agent").  All  capitalized  terms used  herein and not  otherwise
  defined shall have the respective  meanings  provided such terms in the Credit
  Agreement referred to below.

                                      W I T N E S S E T H:
                                      - - - - - - - - - -

        WHEREAS,  the Borrower,  the Banks and the Agent are parties to a Credit
Agreement  dated as of July 25, 1997 (as amended,  modified or  supplemented to
date, the "Credit Agreement");

        WHEREAS, the parties hereto wish to amend the Credit Agreement as herein
provided;

        NOW, THEREFORE, it is agreed:

               1. The  reference to "through  March 31, 1999" in each of Section
8.04(f) and the definition of Available  Amount in Section 10 is changed to read
"from October 29, 1999 through March 31, 2000".

               2. In order to induce the Banks to enter into this Agreement, the
Borrower  represents  and warrants that no Default or Event of Default exists on
the Effective Date referred to below after giving effect to this Agreement.

               3.  This   agreement  is  limited  as  specified  and  shall  not
constitute a  modification,  acceptance or waiver of any other  provision of the
Credit Agreement or any other Credit Document.

               4. This  Agreement may be executed in any number of  counterparts
and by the  different  parties  hereto on separate  counterparts,  each of which
counterparts when executed and delivered shall be an original,  but all of which
shall  together  constitute  one and the  same  instrument.  A  complete  set of
counterparts shall be lodged with the Borrower and the Agent.

               5. THIS  AGREEMENT AND THE RIGHTS AND  OBLIGATIONS OF THE PARTIES
HEREUNDER  SHALL BE CONSTRUED IN ACCORDANCE  WITH AND GOVERNED BY THE LAW OF THE
STATE Of NEW YORK.

               6.  This  Agreement  shall  become  effective  on the  date  (the
"Effective  Date") when each of the Borrower  and the Required  Banks shall have
signed a copy  hereof  (whether  the same or  different  copies)  and shall have
delivered  (including by way of  telecopier) the same to the Agent at its Notice
Office.

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               7. At all times on and after the Effective  Date,  all references
in the Credit Agreement and each of the Credit Documents to the Credit Agreement
shall be deemed to be references to such Credit Agreement after giving effect to
this Agreement.

                                      * * *

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                   IN WITNESS  WHEREOF,  each of the parties hereto has caused a
counterpart  of this  Amendment to be duly executed and delivered as of the date
first above written:

                                             FEDERAL DATA CORPORATION

                                                 /s/ James M. Dean
                                             BY:
                                                 -------------------------------
                                                 Name: James M. Dean
                                                 Title: Vice President and Chief
                                                               Financial Officer

                                             BANKERS TRUST COMPANY, Individually
                                                        and as agent

                                                 /s/ Gregory Shefrin
                                             BY:
                                                 -------------------------------
                                                 Name: Gregory Shefrin
                                                 Title: Principal

                                             IBJ WHITEHALL BANK & TRUST

                                                        COMPANY

                                                 /s/ David Thalmann
                                             BY:
                                                 -------------------------------
                                                 Name: David Thalmann
                                                 Title: Director

                                             BANK AUSTRIA CREDITANSTALT
                                                 CORPORATE FINANCE, INC.

                                                 /s/ Patrick Rounds
                                             BY:
                                                 -------------------------------
                                                 Name: Patrick Rounds
                                                 Title: Vice President

                                                 /s/ James McCann
                                             BY:
                                                 -------------------------------
                                                 Name: James McCann
                                                 Title: Vice President

                                             FIRST SOURCE FINANCIAL LLP

                                                 /s/ David C. Wagner
                                             BY:
                                                 -------------------------------
                                                 Name: David C. Wagner
                                                 Title: Vice President

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                                             BANKBOSTON, N.A.

                                                 /s/ Marie V. Duprey
                                             BY:
                                                 -------------------------------
                                                 Name: Marie V. Duprey
                                                 Title: Vice President

                                             THE BANK OF NEW YORK

                                                 /s/ Ronald R. Reedy
                                             BY:
                                                 -------------------------------
                                                 Name: Ronald R. Reedy
                                                 Title: Vice President

                                             CREDIT LYONNAIS NEW YORK BRANCH

                                                 /s/ Attila Koc
                                             BY:
                                                 -------------------------------
                                                 Name: Attila Koc
                                                 Title: First Vice President

                                             PNC BANK, NATIONAL ASSOCIATION

                                                 /s/ Troy H. Bell
                                             BY:
                                                 -------------------------------
                                                 Name: Troy H. Bell
                                                 Title: Assistant Vice President

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                                             FIRST UNION COMMERCIAL CORP.

                                                 /s/ Barbara Boehm
                                             BY:
                                                 -------------------------------
                                                 Name: Barbara Boehm
                                                 Title: Vice President