Exhibit 5.1 and 23.1


                 [WILLIAMS, MULLEN, CLARK & DOBBINS LETTERHEAD]


                                  June __, 2000


Board of Directors
Southern Financial Bancorp, Inc.
37 East Main Street
Warrenton, Virginia  20186

Ladies and Gentlemen:

         This letter is in reference to the  Registration  Statement on Form S-4
dated June 16,  2000,  filed by Southern  Financial  Bancorp,  Inc.,  a Virginia
Corporation  (the  "Company"),  with  the  Securities  and  Exchange  Commission
pursuant  to  the  Securities  Act  of  1933,  as  amended  (the   "Registration
Statement").  The  Registration  Statement  relates to 409,906  shares of Common
Stock, $0.01 par value per share (the "Shares"), which Shares are proposed to be
offered  to  the   shareholders   of  First   Savings   Bank  of   Virginia,   a
Virginia-chartered  savings  association  ("First  Savings"),   pursuant  to  an
Agreement  and Plan of  Reorganization,  made and  entered  into as of March 31,
2000, by and between First Savings,  the Company, and Southern Financial Bank, a
Virginia state bank and a wholly-owned  subsidiary of the Company, and a related
Plan of Merger (collectively, the "Agreement").

         We have examined such corporate  proceedings,  records and documents as
we considered  necessary  for the purposes of this opinion.  We have relied upon
certificates  of officers of the Company  where we have deemed it  necessary  in
connection with our opinion.

         Based upon such examination,  it is our opinion that the aforementioned
Shares, when issued against payment therefor pursuant to the Agreement,  will be
validly issued,  fully paid and nonassessable under the laws of the Commonwealth
of Virginia.

         We hereby  consent to the  filing of this  opinion as an exhibit to the
Registration Statement and to the reference to our firm under the caption "Legal
Opinion" in the Proxy  Statement/Prospectus  forming a part of the  Registration
Statement.

                                         Very truly yours,


                                         Williams, Mullen, Clark & Dobbins, P.C.


                                         By:____________________________________