LOSS OF SEPARATION OCCURRED BTWN A TBM700 NBOUND HANDED OFF TO ZDC BY PCT TRACON AND A BE53 SBOUND HANDED OFF TO PCT BY ZDC. BOTH ACFT WERE AT 8000 FT.

Narrative

ACFT X WAS NBOUND ON ROUTING MRB V501 AT 8000 FT. ZDC HAD ALREADY ACCEPTED A HDOF PRIOR TO MRB VOR. ZDC CALLED FOR A MANUAL HDOF ON ACFT Y. ACFT Y WAS SBOUND; OPPOSITE DIRECTION; MRB THEN V143. ZDC WAS FLASHING THE ACFT AT THE WRONG SECTOR. I HAD ONLY A LIMITED DATA TAG ON ACFT Y. THE ACFT Y WAS ALREADY XING MY BOUNDARY LINE; ENTERING MY AIRSPACE WITHOUT A HDOF. I TOOK RADAR ON ACFT Y WITHOUT REALIZING HE WAS AT 8000 FT. I MADE ARTS ENTRIES TO ASSIGN THE ACFT TO MY TAG. I THEN SAW THE ALT WAS 8000 FT. I THEN TURNED ACFT X WBOUND AND DSNDED HIM TO 7000 FT TO AVOID THE TFC. I WAS ONLY TALKING TO ACFT X AT THE TIME OF INCIDENT. ACFT X WAS SLOW TURNING AND DSNDING. TFC WAS CALLED TO ACFT X AND HE REPLIED WE HAVE HIM ON TCASII. ACFT Y CHKED IN AND ADVISED ME HE WAS GETTING A TA. HE WAS ABOUT 1 1/2 MI E OF ACFT X AT THE SAME ALT. IF ZDC HAD FLASHED ACFT Y; ON THE CORRECT SCOPE; THIS SIT; MORE THAN LIKELY WOULD HAVE BEEN AVOIDED. HAD ZDC COMPLETED A HDOF PRIOR TO ENTERING MY AIRSPACE; THIS SIT COULD HAVE BEEN AVOIDED. ZDC HAD ALREADY ACCEPTED THE HDOF ON THE TFC I WAS GIVING TO THEM. THEY SHOULD HAVE RESOLVED THE CONFLICTION PRIOR TO MAKING A HDOF WITH ME. ALSO THE ACFT DATA TAG WAS BLOCKED BY ANOTHER DATA TAG WHEN I FIRST OBSERVED IT. ZDC DID COORDINATE 8000 FT ON THE LANDLINE AT THE TIME OF THE MANUAL HDOF. I DID NOT CATCH THE ALT AT THE TIME DUE TO THE CLOSE PROX TO MY AIRSPACE. I WAS TRYING TO HELP OUT ANOTHER CTLR FROM HAVING AN AIRSPACE DEV; NOT REALIZING HE WOULD BE HANDING OFF AN ACFT AT THE SAME ALT I WAS GIVING HIM.