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                                                                 Exhibit (a)(5)

                           Offer to Purchase for Cash

                     All Outstanding Shares of Common Stock

                                       of

                            GRC INTERNATIONAL, INC.

                                       at

                              $15.00 NET PER SHARE

                                       by

                                LMN CORPORATION

                          a wholly owned subsidiary of

                                   AT&T CORP.

     THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, EASTERN
         TIME, ON MONDAY, MARCH 20, 2000, UNLESS THE OFFER IS EXTENDED.

                                                               February 22, 2000

     To Our Clients:

     Enclosed for your consideration are the Offer to Purchase dated February
22, 2000 (the "Offer to Purchase") and the related Letter of Transmittal (which,
as amended or supplemented from time to time, collectively constitute the
"Offer") in connection with the offer by LMN Corporation, a Delaware corporation
(the "Purchaser") and a wholly owned subsidiary of AT&T Corp., a New York
corporation, to purchase all outstanding shares of Common Stock, par value $.10
per share (the "Shares"), of GRC International, Inc., a Delaware corporation
(the "Company"), at a purchase price of $15.00 per Share, net to the seller in
cash, without interest thereon, upon the terms and subject to the conditions set
forth in the Offer to Purchase and in the related Letter of Transmittal enclosed
herewith. Holders of Shares whose certificates for such Shares (the "Share
Certificates") are not immediately available, or who cannot deliver their Share
Certificates and all other required documents to EquiServe (the "Depositary") on
or prior to the Expiration Date (as defined in the Offer to Purchase), or who
cannot complete the procedures for book-entry transfer on a timely basis, must
tender their Shares according to the guaranteed delivery procedures set forth in
Section 3 of the Offer to Purchase.

     WE ARE THE HOLDER OF RECORD OF SHARES HELD BY US FOR YOUR ACCOUNT. A TENDER
OF SUCH SHARES CAN BE MADE ONLY BY US AS THE HOLDER OF RECORD AND PURSUANT TO
YOUR INSTRUCTIONS. THE ENCLOSED LETTER OF TRANSMITTAL IS FURNISHED TO YOU FOR
YOUR INFORMATION ONLY AND CANNOT BE USED BY YOU TO TENDER SHARES HELD BY US FOR
YOUR ACCOUNT.

     Accordingly, we request instructions as to whether you wish to have us
tender on your behalf any or all Shares held by us for your account pursuant to
the terms and conditions set forth in the Offer.

     Please note the following:

          1.  The tender price is $15.00 per Share, net to you in cash, without
     interest thereon, upon the terms and subject to the conditions set forth in
     the Offer.

          2.  The Offer is being made for all outstanding Shares.

          3.  The Board of Directors of the Company has unanimously approved the
     Offer, the Merger (as defined below) and the Merger Agreement (as defined
     below) and determined that the terms of each are advisable, fair to, and in
     the best interests of, the Company and its stockholders, and recommends
     that the Company's stockholders accept the Offer and tender their Shares
     pursuant to the Offer.
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          4.  The Offer is being made pursuant to an Agreement and Plan of
     Merger, dated as of February 14, 2000 (the "Merger Agreement"), among the
     Company, Parent and the Purchaser pursuant to which, following the
     consummation of the Offer and in accordance with the Delaware General
     Corporation Law, and subject to the satisfaction or waiver of certain
     conditions, the Purchaser will be merged with and into the Company (the
     "Merger"), with the Company continuing as the surviving corporation and as
     a wholly owned subsidiary of Parent.

          5.  The Offer is conditioned upon, among other things, (i) there being
     validly tendered and not properly withdrawn prior to the expiration date of
     the Offer at least a majority of the total number of outstanding Shares on
     a fully diluted basis on the date of purchase and (ii) the expiration or
     termination of any applicable waiting periods under the Hart-Scott-Rodino
     Antitrust Improvements Act of 1976, as amended. The Offer is also subject
     to the other conditions set forth in the Offer to Purchase. See the
     Introduction and Section 14 of the Offer to Purchase.

          6.  Any stock transfer taxes applicable to the sale of Shares to the
     Purchaser pursuant to the Offer will be paid by the Purchaser, except as
     otherwise provided in Instruction 6 of the Letter of Transmittal.

          7.  The Offer and withdrawal rights will expire at 12:00 Midnight,
     Eastern time, on Monday, March 20, 2000, unless the Offer is extended.

          8.  Payment for Shares purchased pursuant to the Offer will in all
     cases be made only after timely receipt by the Depositary of (a) Share
     Certificates or timely confirmation of the book-entry transfer of such
     Shares into the account maintained by the Book-Entry Transfer Facility (as
     described in the Offer to Purchase), pursuant to the procedures set forth
     in Section 3 of the Offer to Purchase, (b) the Letter of Transmittal (or a
     facsimile thereof), properly completed and duly executed, with any required
     signature guarantees or an Agent's Message (as defined in the Offer to
     Purchase), in connection with a book-entry delivery and (c) any other
     documents required by the Letter of Transmittal. Accordingly, payment may
     not be made to all tendering stockholders at the same time, depending upon
     when Share Certificates or confirmations of book-entry transfer of such
     Shares into the Depositary's account at the Book-Entry Transfer Facility
     are actually received by the Depositary.

     If you wish to have us tender any or all of the Shares held by us for your
account, please so instruct us by completing, executing, detaching and returning
to us the instruction form set forth on the back page of this letter. If you
authorize the tender of your Shares, all such Shares will be tendered unless
otherwise specified on the back page of this letter. An envelope to return your
instructions to us is enclosed. YOUR INSTRUCTIONS SHOULD BE FORWARDED TO US IN
AMPLE TIME TO PERMIT US TO SUBMIT A TENDER ON YOUR BEHALF PRIOR TO THE
EXPIRATION OF THE OFFER.

     The Purchaser is not aware of any state where the making of the Offer is
prohibited by administrative or judicial action pursuant to any valid state
statute. If the Purchaser becomes aware of any valid state statute prohibiting
the making of the Offer or the acceptance of the Shares pursuant thereto, the
Purchaser will make a good faith effort to comply with such statute or seek to
have such statute declared inapplicable to the Offer. If, after such good faith
effort, the Purchaser cannot comply with such state statute, the Offer will not
be made to (nor will tenders be accepted from or on behalf of) holders of Shares
in such state. In any jurisdiction where the securities, "blue sky" or other
laws require the Offer to be made by a licensed broker or dealer, the Offer
shall be deemed to be made on behalf of the Purchaser by Lehman Brothers Inc.
(the Dealer Manager), or one or more registered brokers or dealers licensed
under the laws of such jurisdiction.
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          Instructions with Respect to the Offer to Purchase for Cash

                     All Outstanding Shares of Common Stock

                                       of

                            GRC INTERNATIONAL, INC.

                                       by

                                LMN CORPORATION

                          a wholly owned subsidiary of

                                   AT&T CORP.

     The undersigned acknowledge(s) receipt of your letter, the enclosed Offer
to Purchase dated February 22, 2000 (the "Offer to Purchase") and the related
Letter of Transmittal (which, as amended or supplemented from time to time,
collectively constitute the "Offer") in connection with the offer by LMN
Corporation, a Delaware corporation (the "Purchaser") and a wholly owned
subsidiary of AT&T Corp., a New York corporation, to purchase all outstanding
shares of Common Stock, par value $.10 per share (the "Shares"), of GRC
International, Inc., a Delaware corporation, at a purchase price of $15.00 per
Share, net to the seller in cash, without interest thereon, upon the terms and
subject to the conditions set forth in the Offer.

     This will instruct you to tender to the Purchaser the number of Shares
indicated below (or if no number is indicated below, all Shares) which are held
by you for the account of the undersigned, upon the terms and subject to the
conditions set forth in the Offer.

          Number of Shares to be Tendered: ------------------ Shares*


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                                   Sign Below

Account Number:
- ------------------ Signature(s)
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Dated:
- ------------------ , 2000

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                          PLEASE TYPE OR PRINT NAME(S)

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                     PLEASE TYPE OR PRINT ADDRESS(ES) HERE

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                       AREA CODE AND TELEPHONE NUMBER(S)

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              TAXPAYER IDENTIFICATION OR SOCIAL SECURITY NUMBER(S)

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* Unless otherwise indicated, it will be assumed that you instruct us to tender
  all Shares held by us for your account.