<PAGE>
 
                           SWINGLINE PROMISSORY NOTE
                           -------------------------



$50,000,000               Date: February 10, 1999


     FOR VALUE RECEIVED, the undersigned, THE WMF GROUP, LTD., a Delaware
corporation, WMF WASHINGTON MORTGAGE CORP., a Delaware corporation; WMF/HUNTOON,
PAIGE ASSOCIATES LIMITED, a Delaware corporation; WMF PROCTOR, LTD., a Michigan
corporation; THE ROBERT C. WILSON COMPANY, a Texas corporation; THE ROBERT C.
WILSON-ARIZONA COMPANY, an Arizona corporation and WMF CARBON MESA ADVISORS,
INC., a Delaware corporation (herein called the "Borrowers", and individually as
"Co-Borrowers"), hereby promises to pay to the order of RESIDENTIAL FUNDING
CORPORATION, a Delaware corporation (the "Lender" or, together with its
successors and assigns, the "Holder") at the offices of RESIDENTIAL FUNDING
CORPORATION (the "Credit Agent") at 8400 Normandale Lake Blvd., Suite 600,
Minneapolis, Minnesota 55437, or at such other place as the Holder may designate
from time to time, the principal sum of Fifty Million Dollars ($50,000,000) or
so much thereof as may be outstanding from time to time pursuant to the
Warehousing Credit and Security Agreement described below, and to pay interest
on said principal sum or such part thereof as shall remain unpaid from time to
time, from the date of each Advance until repaid in full, and all other fees and
charges due under the Agreement, at the rate and at the times set forth in the
Agreement. All payments hereunder shall be made in lawful money of the United
States and in immediately available funds.

     This Note is given to evidence an actual warehouse line of credit in the
above amount and is the Swingline Note referred to in that certain Credit and
Security Agreement (Syndicated Agreement) (the "Agreement") dated the date
hereof by and among the Borrowers, the Lenders named therein, and the Credit
Agent, as credit agent for the Lenders, as the same may be amended or
supplemented from time to time, and is entitled to the benefits thereof.
Reference is hereby made to the Agreement (which is incorporated herein by
reference as fully and with the same effect as if set forth herein at length)
for a description of the Collateral, a statement of the covenants and
agreements, a statement of the rights and remedies and securities afforded
thereby and other matters contained therein. Capitalized terms used herein,
unless otherwise defined herein, shall have the meanings given them in the
Agreement.

     This Note may be prepaid in whole or in part at any time without premium or
penalty.
<PAGE>
 
     Should this Note be placed in the hands of attorneys for collection, the
Borrowers agree to pay, in addition to principal and interest, fees and charges
due under the Agreement, any and all costs of collecting this Note, including
reasonable attorneys' fees and expenses.

     The Borrowers hereby waive demand, notice, protest and presentment.

     The promises and agreements herein shall be construed to be and are hereby
declared to be the joint and several promises and agreements of each Co-Borrower
and shall constitute the joint and several obligation of each Co-Borrower and
shall be fully binding upon and enforceable against each Co-Borrower. The
release of any party to this Note shall not affect or release the joint and
several liability of any other party. The Lender may at its option enforce this
Note against one or all of the Co-Borrower, and the Lender shall not be required
to resort to enforcement against each Co-Borrower and the failure to proceed
against or join each Co-Borrower shall not affect the joint and several
liability of each Co-Borrower.

     This Note shall be construed and enforced in accordance with the laws of
the State of Minnesota, without reference to its principles of conflicts of law.

     IN WITNESS WHEREOF, the Borrowers have executed this Note as of the day and
year first above written.


                              THE WMF GROUP, LTD.,
                              a Delaware corporation
                              (on behalf of the Borrowers)


                              By:___________________

                              Its:__________________


STATE OF _______________ )
                         ) ss
COUNTY OF ______________ )

     On ______________________, before me, a Notary Public, personally appeared
________________________________, the ______________________ of THE WMF GROUP,
LTD., a Delaware corporation, personally known to me (or proved to me on the
basis of satisfactory evidence) to be the person whose name is subscribed to the
within instrument
<PAGE>
 
and acknowledged to me that he/she executed the same in his/her authorized
capacity, and that by his/her signature on the instrument the person, or the
entity upon behalf of which the person acted, executed the instrument.

     WITNESS my hand and official seal.


______________________________
                              Notary Public
 (SEAL)                       My Commission Expires:_____________