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                                                                  EXHIBIT 10.13

                                                                  EXECUTION COPY

                               BECHTEL CORPORATION
                               5275 Westview Drive
                            Frederick, Maryland 21703

                                                           October 1, 2001


Metromedia Fiber Network, Inc.
360 Hamilton Avenue
White Plains, New York 10601

            Reference is hereby made to the Master Restructuring Agreement (the
"MRA"), dated as of October 1, 2001, by and among Metromedia Fiber Network, Inc.
("MFN"), Metromedia Fiber Network Services, Inc. ("MFNS") and Bechtel
Corporation ("Bechtel"). Capitalized terms not otherwise defined herein shall
have the meaning ascribed to them in the MRA.

            The amount owing to Bechtel and being restructured pursuant to the
MRA consists of $98 million plus the Liquidated Damages Amount. The $98 million
consists of (i) approximately $55 million for outstanding invoices (schedule of
invoices attached) and (ii) additional work and related costs and expenses
incurred under the Master Services Agreement (the "MSA"), estimated by Bechtel
to be owing, which amount the parties believe on the date hereof to be $43
million (the "Estimated Amount").

            Notwithstanding the terms of the MRA, we agree to act in good faith
to jointly reconcile and agree on the Agreed Amount (as defined) below. This
process will not involve a review of the quality or performance of services (the
warranty provisions contained in the MSA for those issues shall govern those
issues) but will be limited to a review and reconciliation of the actual total
costs (labor, non-labor, subcontractor and vendor) and claims incurred by
Bechtel or for which it is responsible pursuant to the MSA. The parties agree to
cooperate and work in good faith to complete the reconciliation as soon as
reasonably possible but in any event by December 31, 2001. At that point any
remaining disputes will be resolved in accordance with dispute resolution
process outlined in Article XIII of the MSA and determined at the end of that
process. The parties agree that in no event will the reconciliation increase or
decrease the Estimated Amount by an aggregate amount of more than $10 million.

            If the Note has not been converted or transferred by Bechtel, in
whole or in part, prior to the date (the "Reconciliation Date") that the parties
hereto agree upon the reconciliation of the Estimated Amount with the actual
costs and expenses for additional work and related expenses under the MSA (such
agreed upon reconciled amount being, the "Agreed Amount"), and it is determined
that the Agreed Amount is (i) less than the Estimated Amount, then the Note will
be exchanged for a new note with the same terms as the Note, except that the
principal amount of the new note will be reduced (subject to the limitation in
this letter agreement) to reflect the Agreed Amount and to give MFNS credit for
any payments of principal and interest that have been made to Bechtel pursuant
to the Note, or (ii) greater than the Estimated Amount, then the Note will be
exchanged for a new note with the same terms as the Note, except that the
principal amount will be increased (subject to the limitations set forth in this
letter agreement) to

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reflect the Agreed Amount and MFNS shall pay to Bechtel by wire transfer in
immediately available funds, the amount that MFNS would have otherwise been
obligated to pay to Bechtel if, on the Closing Date, the Note issued to Bechtel
reflected the Agreed Amount. Any new note issued in accordance with this
paragraph shall be the "New Note".

            If the Note has been converted or transferred by Bechtel, in whole
or in part, prior to the Reconciliation Date, the difference between the
Estimated Amount and Agreed Amount (the "True-Up Amount") will be evidenced by a
new note (the "True-up Note"), made by the party owing the True-Up Amount. If a
True-Up Note is required to be made by MFNS, the principal amount of the True-Up
Note shall be equal to the True-Up Amount and shall be made on the same terms as
the Note and MFNS shall pay to Bechtel by wire transfer in immediately available
funds, the amount that MFNS would have otherwise been obligated to pay to
Bechtel if, on the Closing Date, the Note issued to Bechtel reflected the
True-Up Amount. If a True-Up Note is required to be made by Bechtel, the
principal amount of the True-Up Note shall be equal to the True-Up Amount plus
any amounts of principal and interest that have been made to Bechtel pursuant to
the Note that would not have been required to be made by MFNS if the principal
amount of the Note issued on the Closing Date had been reduced by the True-Up
Amount (the "Bechtel True-Up Note"). The Bechtel True-Up Note shall bear
interest at a rate of 8.5% per annum and principal shall be amortized at the
same rate as the Note. The payment obligations under the Note and the True-Up
Note may be set off one against the other, but the conversion rights and other
rights of Bechtel, its successors and/or assigns under the Note shall otherwise
remain as set out in the Note without regard to the True-up Note. If MFN or MFNS
default in the performance of any obligations under the Transactions Documents,
Bechtel will be entitled to set off any amounts owed by it pursuant to the
True-Up Note (if it is determined that such a note is required to be made by it)
or other claims it may owe to MFN or MFNS, against any obligations owing to
Bechtel under Transaction Documents.

            This letter does not in any way amend or diminish Bechtel's rights
under or pursuant to the Note for its full face amount, including its conversion
rights and payment obligations unless and until Bechtel agrees to and does
adjust the Note in accordance with this letter agreement. Any dispute in the
True-Up Amount (the True-Up Amount will be considered in dispute until the
parties expressly agree to, issue, execute, deliver and accept the True-up Note
or the New Note, as the case may be, or as otherwise agreed to in writing by
each of the parties hereto) shall be considered a separate and independent claim
without right of set-off to, adjustment of or other effect on Bechtel's rights
under the Note or its right to convert or transfer the Note in accordance with
its express terms and without regard to this letter.

            If you agree with the foregoing, please sign and return a copy of
this letter.



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                                    Yours very truly,

                                    BECHTEL CORPORATION


                                    By: /s/ George E. Conniff
                                       -----------------------------------------
                                       Name:  George E. Conniff
                                       Title: President, Telecommunications and
                                                         Industrial

Accepted and Agreed:

METROMEDIA FIBER NETWORK SERVICES, INC.



By: /s/ Nick Tanzi
   _____________________________________
      Name: Nick Tanzi
      Title: President & CEO



METROMEDIA FIBER NETWORK, INC.



By: /s/ Nick Tanzi
   _____________________________________
      Name: Nick Tanzi
      Title: President & CEO




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