ZDC RADAR CTLR HANDED OFF VFR C337 TO GSB APCH. A SHORT TIME LATER GSB MADE A HDOF TO DC9 ON AN IFR PA32 DSNDING INTO THE C337 RESULTING IN AN NMAC.

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ACFT X; C377; WAS PROCEEDING SW ALONG V1 IN THE ZDC EWN (25) SECTOR VFR AT 4500 FT. THIS ACFT WAS HANDED OFF TO GSB APCH AND COM XFERRED AT ABOUT 15 MI NE OF ISO VOR; ABOUT 3 OR 4 MI FROM GSB APCH AIRSPACE. GSB INITIATED A HDOF TO ME ON ACFT Y; PA32 IFR LNDG PGV. HDOF IS ACCEPTED WHEN ACFT Y IS OUT OF APPROX 7000 FT FOR 3000 FT (15 MI S OF PGV ARPT). ACFT CAME UP ON MY FREQ (AT THIS TIME THE C377 WAS AT ACFT Y'S 12 O'CLOCK AND 4 MI HEAD ON!). ACFT Y CHKED IN OUT OF ABOUT 5000 FT DSNDING TO 3000 FT. MY FIRST XMISSION WAS 'HAD GSB CALLED THE TFC AT 12 O'CLOCK AND 4 MI TO HIM.' HE REPLIED 'ABOUT 15 MI AGO' AND ASKED IF HE SHOULD TURN. I TURNED THE ACFT 110 DEGS L AND CONTINUED TO CALL TFC; DSNDING THE ACFT TO 2200 FT. ACFT Y NEVER SAW THE C377 TFC SO I TURNED HIM ANOTHER 20 DEGS L TO ENSURE THE TARGETS WOULDN'T MERGE (FIGURING THE CESSNA PLT MAY INITIATE AN EVASIVE MANEUVER). THE TARGETS MISSED BY APPROX 1/4 MI -- IT WAS CLOSE. OUT OF AROUND 3600-3700 FT; ACFT Y WAS ADVISED 'PREVIOUS TFC NO FACTOR' AND VECTORED FOR PGV. GSB APCH HAD RADAR AND COMS ON BOTH OF THESE ACFT IN THEIR AIRSPACE. THEY WERE HEAD-ON WITH ONE DSNDING THROUGH THE OTHER; WITH TARGETS THAT WERE GOING TO MERGE. GSB SHOULD HAVE MADE MORE THAN 1 TFC CALL TO THE IFR; NOT JUST ADVISE ONCE AND FORGET ABOUT IT. MERGING TARGET PROCS SHOULD'VE BEEN FOLLOWED BY GSB. A SMALL BIT OF COMMON SENSE WOULD'VE ALSO HELPED IN THIS INSTANCE -- PERHAPS STOPPING ACFT Y AT 6000 FT UNTIL HE HAD THE TFC; ANOTHER TFC CALL -- ANYTHING! SEPARATE KNOWN TFC! THIS COULD HAVE VERY EASILY BEEN A MAC.