AMENDED AND RESTATED
                      GUARANTY OF PAYMENT

          To induce UNITED BANK, Vienna, Virginia (the "Bank") to
continue to extend credit and other financial accommodations to
HADRON, INC., a New York corporation, AVENUE TECHNOLOGIES, INC.,
a Virginia corporation, VAIL RESEARCH AND TECHNOLOGY CORPORATION,
a Virginia corporation,  SYCOM SERVICES, INC., a Delaware
corporation, and ENGINEERING & INFORMATION SERVICES, INC., a
Virginia corporation (hereinafter individually and collectively
called the "Debtor"), and to forbear in the exercise of its
rights against the Debtor, and for other good and valuable
consideration, the receipt and sufficiency of which are hereby
acknowledged, each of the undersigned jointly and severally
(hereinafter individually and collectively called the
"Guarantors"), hereby unconditionally guaranty to the Bank the
full and prompt payment at maturity, including accelerated or
extended maturity, of all Obligations, as hereinafter defined, of
the Debtor to the Bank; provided, however, that the Guarantors'
liability on the Obligations shall not exceed the lesser of (i)
50% of the principal amount thereof from time to time
outstanding, plus interest thereon and fees associated therewith,
and (ii)  $750,000 of the principal amount thereof from time to
time outstanding, plus interest thereon and fees associated
therewith.  A reduction in the amount of the Obligations shall
not reduce, pro rata or pro tanto, the Guarantors' obligation
under this Guaranty except to the extent of payments by the
Guarantor in satisfaction of the Guarantors' obligation
hereunder.  The term "Obligations" means all indebtedness,
obligations and liabilities of the Debtor to the Bank now
existing or hereafter created or arising, whether direct or
indirect, absolute or contingent, joint or several, secured or
unsecured, liquidated or unliquidated, and evidenced by (i) that
certain Commercial Note dated June 29, 1999 from the Debtor
payable to the order of the Bank in the original amount of
$1,500,000.00, (ii) that certain Revolving Commercial Note dated
June 29, 1999 from the Debtor payable to the order of the Bank in
the original amount of $1,500,000.00, and (iii) renewals,
increases, extensions, and modifications thereof and
substitutions therefor.

          The Bank may at any time and from time to time, without
the consent of or notice to the Guarantors, without incurring
liability to the Guarantors, and without affecting, impairing or
releasing the obligations of the Guarantors hereunder, renew,
extend, change the manner, time, place, and terms of payment,
grant indulgences in connection with, settle, compromise, sell,
exchange, substitute, release, surrender, subordinate, or
exercise or refrain from exercising any rights with respect to,
any of the Obligations, any security therefor, the obligation of
any of the Guarantors hereunder or any other party primarily or
secondarily liable for any of the Obligations.

          The liability of the Guarantors shall not be affected,
impaired or released by (i) any failure, neglect or omission by
the Bank to realize upon or collect any of the Obligations, any
obligation hereunder, or any security for or guaranty of the
Obligations or any obligation hereunder, or to exercise any
remedies of setoff or otherwise that it may have with respect to
property of the Debtor possessed by the Bank, (ii) any defense
the Debtor or any other party primarily or secondarily liable for
any of the Obligations might have to the payment of the
Obligations, (iii) any determination that any lien taken, or
attempted to be taken, by the Bank to secure the Obligations is
invalid or unperfected, (iv) any determination that any party
executing any evidence of any of the Obligations on behalf of the
Debtor was without power or authority to do so or that for any
other reason the Obligations, any security therefor, or any other
guaranty thereof, are invalid or unenforceable, or (v) any
defenses the Debtor may have or assert to the Obligations.  It is
understood that nothing shall discharge or satisfy the
Guarantors' liability hereunder except the full performance and
payment of all Obligations with interest and expenses, or the
Bank's written release of the Guarantors' liability.

          The Guarantors' liability hereunder shall not be
affected, impaired or released by the filing of a petition by or
against the Debtor under the provisions of any bankruptcy,
reorganization, arrangement, insolvency, liquidation or similar
law for relief of debtors, and upon the filing of such petition,
for the purpose of this Guaranty, all Obligations, at the option
of the Bank, shall be immediately due and payable.

          The Guarantors represent and covenant that they are and
shall remain independently informed of the financial condition of
the Debtor and all other circumstances which bear on the risk of
non-payment of the Obligations.  The Guarantors waive any right
to require the Bank to disclose to them any information the Bank
has or may have in the future concerning such condition or
circumstances.

          The Guarantors subordinate all obligations of the
Debtor owing to them or any of them, whether now existing or
hereafter arising, to all Obligations of the Debtor to the Bank.

          The Guarantors unconditionally waive any right they may
have to be subrogated to the rights of the Bank against the
Debtor with respect to any payment by the Guarantors hereunder,
and further unconditionally waive any right they may have of
reimbursement or indemnification from the Debtor with respect to
any such payment.

          If at any time any payment by the Debtor of any
Obligation is rescinded or must otherwise be restored or returned
upon the insolvency, bankruptcy, dissolution, liquidation or
reorganization of the Debtor or upon or as a result of the
appointment of a receiver, intervener or conservator of, or
trustee or similar officer for, the Debtor or any substantial
part of its property or otherwise, the Guarantors' obligations
hereunder with respect to such payment shall be reinstated as
though such payment had been due but not made at such time.

          The Guarantors waive (i) notice of acceptance of this
Guaranty, (ii) notice of the existence or creation of the
Obligations, (iii) presentment and demand for payment of any of
the Obligations, (iv) protest and notice of dishonor and protest
and any other notice to the Guarantors or to any other party with
respect to the Obligations, and (v) the benefit of their
homestead exemptions and any other exemptions with respect to the
Obligations.

          This is a guaranty of payment and not of collection.
The Guarantors waive any right, including without limitation any
right arising from Section 49-25 or 49-26 of the Code of
Virginia, to require that the Bank bring action against the
Debtor or any other party or to require that the Bank resort to
any security or to any balance of any deposit account or credit
on the books of the Bank in favor of Debtor or any other party.

          All payments, whether voluntary or involuntary,
received by the Bank from the Debtor, Guarantors, or any other
source, including amounts realized from security and deposit
account balances, may be applied by the Bank to any of the
Obligations, or any other obligations of the Guarantors or any
other obligor, in whatever order the Bank elects.

          The Bank may, without notice to or consent of the
Guarantors, assign or transfer all or any part of the Obliga
tions, and this Guaranty will inure to the benefit of the Bank's
assignee or transferee to the extent of such assignment or trans
fer; provided, however, that the Bank shall continue to have an
unimpaired right, superior to that of any such assignee or trans
feree, to enforce this Guaranty as to that part of the Obliga
tions the Bank has not assigned or transferred.

          The Bank will have the right, in addition to any
remedies permitted by law (including, without limitation, other
rights of set-off), to set off the amount now or hereafter due
under this Guaranty against any and all accounts, credits, money,
securities, or other property now or hereafter on deposit with,
held by, or in possession of the Bank to the credit of or for the
account of each of the Guarantors, without notice to or consent
by the Guarantors.  In addition to the right of set-off, to
secure the payment of their obligations under this Guaranty, each
of the Guarantors hereby assigns and grants to the Bank a
security interest in all accounts, credit, money, securities, or
other property now or hereafter on deposit with, held by, or in
the possession of the Bank to the credit of or for the account of
such Guarantor.

          The Guarantors shall pay to the Bank on demand all
costs incurred by the Bank, and reasonable attorneys' fees, in
the collection or enforcement of this Guaranty, whether or not
suit is brought.

          The Guarantors agree to furnish the Bank, in form
acceptable to the Bank, (i) a signed, current personal financial
statement and personal federal income tax return annually, within
30 days after the filing of the latter, and (ii) such other
financial information and data as the Bank may from time to time
request.

          THE GUARANTORS IRREVOCABLY AND UNCONDITIONALLY WAIVE
ANY RIGHT THEY MAY HAVE TO TRIAL BY JURY IN ANY SUIT, ACTION,
PROCEEDING, OR COUNTERCLAIM ARISING OUT OF OR RELATING TO THIS
GUARANTY, WHETHER SUCH SUIT, ACTION, PROCEEDING, OR COUNTERCLAIM
IS INSTITUTED BY THE BANK, THE GUARANTORS OR ANY OTHER PARTY.

          The Guarantors irrevocably (i) submit to the juris
diction of any Virginia state court or federal court sitting in
the state of Virginia with respect to any suit, action, or
proceeding relating to this Guaranty, (ii) waive any objection
which the Guarantors may now or hereafter have to the laying of
venue of any such suit, action, or proceeding brought in any such
court and any claim that any such suit, action or proceeding
brought in any such court has been brought in an inconvenient
forum, (iii) waive the right to object that any such court does
not have jurisdiction over the Guarantors, and (iv) consent to
the service of process in any such suit, action, or proceeding by
the mailing of copies of such process to the Guarantors by
certified mail at the Guarantors' addresses indicated in this
Guaranty or at such other addresses of which the Bank shall have
received notice.  Nothing in this paragraph shall affect the
Bank's right to serve process in any other manner permitted by
law or to bring proceedings against the Guarantors in any other
court having jurisdiction.

          The rights and remedies of the Bank under this Guaranty
and applicable law shall be cumulative and concurrent and the
exercise of any one or more of them shall not preclude the simul
taneous or later exercise by the Bank of any or all such other
rights or remedies.  In the event any provision of this Guaranty
is held to be invalid, illegal, or unenforceable for any reason,
then such provision only shall be deemed null and void and shall
not affect any other provisions of this Guaranty, which shall
remain effective.  No modification or waiver of any provision of
this Guaranty shall be effective unless it is in writing and
signed by the Bank, and any such waiver shall be effective only
in the specific instance and for the specific purpose for which
it is given.  The failure of the Bank to exercise any option,
right or remedy, in any one or more instances, or the acceptance
by the Bank of partial payments or partial performance, shall not
constitute a waiver of the right to exercise any option, right or
remedy at any time.  The nouns, pronouns and verbs used in this
Guaranty shall be construed as being of such number and gender as
the context may require.

          This Guaranty is an amendment and restatement of that
certain Guaranty of Payment dated June 29, 1999 from the
Guarantors to the Bank (the "Previous Guaranty").  The Guarantors
acknowledge and agree that there are no setoffs or defenses to
the Previous Guaranty and that this Guaranty is not intended as a
novation of the Previous Guaranty.

          This Guaranty shall be governed by and construed in
accordance with the laws of Virginia.


              [Signatures appear on following page]
<PAGE>

          Witness the following signatures and seals this 12th
day of April 2000.

                                 /S/ C.W. GILLULY
                                 -----------------------   [SEAL]
                                   C.W. GILLULY
                                   SS #: ###-##-####
Address:  415 First Street, S.E.
          Washington, D.C. 20003-1827

                                 /S/ MARTHA ALICE GILLULY
                                 -----------------------   [SEAL]
                                   MARTHA ALICE GILLULY
                                   SS #: ###-##-####


COUNTY/CITY OF FAIRFAX
STATE OF VIRGINIA

               The foregoing instrument was acknowledged before
me this 12TH day of APRIL 2000, by C.W. Gilluly
and Martha Alice Gilluly.




                                   /S/ CARIDAD C. MILLER
                                   -----------------------------------
                                   Notary Public

My Commission expires: 12-31-02