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                                                                  Exhibit 4


                  [WASSERSTEIN PERELLA & CO., INC. LETTERHEAD]

                               September 12, 1997


TRW Inc.
1900 Richmond Way
Cleveland, OH  44124


Dear Gentlemen:

     Wasserstein Perella & Co., Inc. ("WP&Co.") is acting on behalf of BDM
International, Inc. (the "Company") to explore the possible sale of the Company
(the "Transaction"). In that connection, you have requested certain information
concerning the Company from officers, directors, employees and/or agents of the
Company, including WP&Co. All such information (whether written or oral)
furnished to you and your Representatives (as defined below), by the Company,
its officers, directors, employees or agents, on or following the date hereof,
which is marked as "confidential" or, if furnished orally, is contemporaneously
identified in writing as being confidential, together with analyses,
compilations, forecasts, studies or other documents or records prepared by you
or your Representatives which contain, are based on or otherwise reflect or are
generated in whole or in part from such information, including that stored on
any computer, word processor or other similar device, are collectively referred
to herein as the "Evaluation Material."

     You hereby agree as follows:

      (1) You shall use the Evaluation Material solely for the purpose of
          evaluating the Transaction and you shall keep the Evaluation Material
          confidential, except that you may disclose the Evaluation Material or
          portions thereof to those of your directors, officers, employees,
          affiliates, representatives (including, without limitation, financial
          advisors, attorneys and accountants) and your potential sources of
          financing (if any) for the Transaction (collectively, the
          "Representatives") (a) who need to know such information for the
          purpose of evaluating the Transaction, (b) who are informed by you of
          the confidential nature of the Evaluation Material and (c) who agree
          to be bound by the terms of this agreement as if they were parties
          hereto. You shall be responsible for any breach of this agreement by
          your Representatives. In the event that you or any of your
          Representatives are requested or required (by deposition,
          interrogatory,


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          request for documents, subpoena, civil investigative demand or similar
          process) to disclose any of the Evaluation Material, you shall provide
          the Company with prompt prior written notice of such requirement, you
          shall furnish only that portion of the Evaluation Material which you
          are advised by written opinion of counsel is legally required, and you
          shall exercise your best efforts to obtain reliable assurance that
          confidential treatment will be accorded such Evaluation Material.

      (2) If you determine not to proceed with the Transaction, you will
          promptly inform WP&Co. of that decision and, in that case or at any
          time upon the request of the Company or WP&Co., you and your
          representatives shall promptly either (i) destroy all copies of the
          written Evaluation Material in your or their possession or under your
          or their custody or control (including that stored in any computer,
          word processor or similar device) and confirm such destruction to the
          Company in writing or (ii) return to WP&Co. all copies of the
          Evaluation Material furnished to you by or on behalf of the Company in
          your possession or in the possession of your Representatives. Any oral
          Evaluation Material will continue to be held subject to the terms of
          this agreement. If requested, you shall provide a certification by an
          appropriate officer that all such Evaluation Material has been
          returned or destroyed.

      (3) The term "Evaluation Material" does not include any information which
          (i) is generally available to and known by the public (other than as a
          result of a disclosure by you or by any of the Representatives); (ii)
          was available to you on a non-confidential basis from a source (other
          than the Company or its representatives) that is not and was not
          prohibited from disclosing such information to you by a contractual,
          legal or fiduciary obligation; or was known to you prior to your
          receipt thereof.

      (4) The parties hereto both agree that, without the prior written consent
          of the other party, neither party nor their representatives shall
          disclose to any person (unless required by law) (a) that any
          investigations, discussions or negotiations are taking place
          concerning the Transaction or any other possible Transaction involving
          the Company and you, (b) that you have requested or received any
          Evaluation Material or (c) any of the terms, conditions or other facts
          with respect to the Transaction involving you or such investigations,
          discussions or negotiations, including the status thereof. The term
          "person" as used in this agreement shall be broadly interpreted to
          include the media and any corporation, partnership, group, individual
          or entity.

      (5) You agree that (i) all communication regarding the Transaction, (ii)
          requests for additional information, facility tours or management
          meetings, and (iii) discussions or questions regarding procedures with
          respect to the Transaction, will be first submitted or directed to
          WP&Co.


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          and not to the Company. Accordingly, you agree that until the
          consummation of the Transaction by you or a third party, you will not,
          directly or indirectly, contact or communicate with any officer,
          director, employee or agent of the Company without the express prior
          consent of the Company or WP&Co. Both parties agree that, for a period
          of one year from the date of this agreement, neither party will,
          directly or indirectly, solicit for employment or hire any employee of
          either party with whom the parties have had contact or who became
          known to the parties in connection with the parties' consideration of
          the Transaction. For purposes of this paragraph, the term "solicit"
          shall not include general solicitations of employment by means of
          newspaper, periodical or trade publication used in the ordinary course
          of business. You acknowledge and agree that (a) WP&Co. and the Company
          are free to conduct the process leading up to a possible Transaction
          as WP&Co. and the Company, in their sole discretion, may determine
          (including, without limitation, by negotiating with any prospective
          buyer and entering into a preliminary or definitive agreement without
          prior notice to you or any other person), (b) WP&Co. and the Company
          reserve the right, in their sole discretion, to change the procedures
          relating to your consideration of the Transaction at any time without
          prior notice to you or any other person, to reject any and all
          proposals made by you or any of your Representatives with regard to
          the Transaction, and to terminate discussions and negotiations with
          you at any time and for any reason, and (c) unless and until a written
          definitive agreement concerning the Transaction has been executed,
          neither WP&Co. nor the Company, nor their respective officers,
          directors, employees, affiliates, stockholders, agents or controlling
          persons will have any legal obligation to you of any kind whatsoever
          with respect to the Transaction, whether by virtue of this agreement,
          any other written or oral expression with respect to the Transaction
          or otherwise. For purposes hereof, the term "definitive agreement"
          does not include an executed letter or intent or any other preliminary
          written agreement.

      (6) You agree that, for a period of two years from the date of this
          agreement, unless such shall have been specifically invited in writing
          by the Company, neither you nor any of your affiliates (as such term
          is defined under the Securities Exchange Act of 1934, as amended (the
          "1934 Act")) or Representatives will in any manner, directly or
          indirectly, (a) effect or seek, offer or propose (whether publicly or
          otherwise) to effect, or cause or participate in or in any way assist
          any other person to effect or seek, offer or propose (whether publicly
          or otherwise) to effect or participate in, (i) any acquisition of any
          securities (or of beneficial ownership thereof) in excess of 5% of the
          Company, or assets of the Company or any of its subsidiaries; (ii) any
          tender or exchange offer, merger or other business combination
          involving the Company or any of its subsidiaries; (iii) any
          recapitalization, restructuring, liquidation,


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          dissolution or other extraordinary Transaction with respect to the
          Company or any of its subsidiaries; or (iv) any solicitation of
          proxies or consents to vote any voting securities of the Company; (b)
          form, join or in any way participate in a "group" (as defined under
          the 1934 Act); (c) take any action which might force the Company to
          make a public announcement regarding any of the types of matters set
          forth in (a) above; or (d) enter into any discussions or arrangements
          with any third party with respect to any of the foregoing. This
          paragraph shall not apply to TRW Investment Management Co., it's
          advisors, or TRW's employee benefit plans.

      (7) You acknowledge that you and your Representatives may receive material
          non-public information in connection with your evaluation of the
          Transaction and you are aware (and you will so advise your
          Representatives) that the United States securities laws impose
          restrictions on trading in securities when in possession of such
          information.

      (8) You understand and acknowledge that none of the Company, WP&Co. or any
          of their respective officers, directors, employees, affiliates,
          stockholders, agents or controlling persons is making any
          representation or warranty, express or implied, as to the accuracy or
          completeness of the Evaluation Material, and each of the Company,
          WP&Co. and such other persons expressly disclaims any and all
          liability to you or any other person that may be based upon or relate
          to (a) the use of the Evaluation Material by you or any of the
          Representatives or (b) any errors therein or omissions therefrom. You
          further agree that you are not entitled to rely on the accuracy and
          completeness of the Evaluation Material and that you will be entitled
          to rely solely on those particular representations and warranties, if
          any, that are made to a purchaser in a definitive agreement relating
          to the Transaction when, as, and if it is executed, and subject to
          such limitations and restrictions as may be specified in such
          definitive agreement.

      (9) Both parties acknowledge that remedies at law may be inadequate to
          protect either party against any actual or threatened breach of this
          agreement. Without prejudice to any other rights and remedies
          otherwise available to either party, both parties agree that the other
          party is entitled to equitable relief in the event of any such breach.

     (10) You agree that no failure to delay by the Company in exercising any
          right, power or privilege hereunder will operate as a waiver thereof,
          nor will any single or partial exercise thereof preclude any other or
          further exercise thereof or the exercise of any other right, power or
          privilege hereunder.


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     (11) This agreement is for the benefit of the parties and their respective
          successors and assigns. The rights of the Company under this agreement
          may be assigned in whole or in part to any purchaser of the Company
          which purchaser shall be entitled to enforce this agreement to the
          same extent and in the same manner as the Company is entitled to
          enforce this agreement.

     (12) This agreement and all controversies arising from or relating to
          performance under this agreement shall be governed by and construed in
          accordance with the laws of the State of New York, without giving
          effect to its conflicts of laws principles.

     (13) This agreement contains the entire agreement between you and the
          Company concerning the subject matter hereof, and no modification of
          this agreement or wavier of the terms and conditions hereof will be
          binding unless approved in writing by the Company and you.

     (14) The obligations of the parties will continue in effect from the date
          of this agreement through September 12, 1999.

     Please confirm your agreement to the foregoing by signing both copies of
this agreement and returning one to WP&Co., Attn: Paul J. S. Haigney.

                                        Very truly yours,

                                        WASSERSTEIN PERELLA & CO., INC.

                                        As Financial Advisor to, and as
                                        Representative of
                                        BDM International, Inc.

                                        By: /s/ Paul J. S. Haigney
                                            ------------------------------------
                                            Paul J. S. Haigney
                                            Managing Director


CONFIRMED AND AGREED AS
OF THE DATE WRITTEN ABOVE:

TRW Inc.

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