C182 EXPERIENCED NMAC DURING IFR FLT AT 6000 FT IN PCT'S AIRSPACE.

Narrative

I WAS ON AN IFR FLT PLAN FROM CGE TO GAI WBOUND AT 6000 FT ON V93 BTWN THE GRACO INTXN AND THE BAL VOR IN VMC. I WAS APPROX 11 MI E OF THE BAL VOR; PLACING ME NEAR ANNAPOLIS; MD; TO MY L. ATC BEGAN A REPEATED EXCHANGE OF COMS WITH WHAT APPEARED TO BE VFR TFC; INDICATING THAT THEY NEEDED TO PERFORM A FLY-BY AT THE ANNAPOLIS STADIUM AT A SPECIFIED TIME AND AT ONE POINT; ASKED IF THEY COULD HAVE FLT FOLLOWING. IN THE COURSE OF THE CONVERSATION; ATC INDICATED THAT THIS WAS IN THE ADIZ AND A FLT PLAN WAS REQUIRED. ATC THEN BEGAN TO COMMUNICATE WITH AN ACFT INDICATING THAT TFC WAS WBOUND AT 6000 FT. BELIEVING THAT ATC WAS REFERRING TO MY ACFT; I BEGAN A MORE INTENSE SEARCH FOR TFC. ALMOST IMMEDIATELY; I SAW AN ACFT AT MY 12 O'CLOCK; SAME ALT; IN A SLIGHT R BANK THAT PASSED TO MY L IN LESS THAN 2 SECONDS. HORIZ SEPARATION WAS APPROX 200 FT. I IMMEDIATELY BANKED TO MY R AND COMMUNICATED TO ATC THAT I HAD TFC IN SIGHT AND THAT WAS VERY CLOSE. ATC THEN COMMUNICATED TO ME THAT THE TFC SEPARATION PROB WAS HIS FAULT. ATC COMMUNICATED THE SAME MESSAGE TO THE OTHER ACFT. THE FLT CONTINUED AS PLANNED TO GAI. THERE WAS SOME CONCERN AS TO THE LOCATION OF THE VFR TFC REQUESTING THE FLY-BY. I BELIEVED THIS TFC WAS MUCH LOWER; BUT ITS LOCATION WAS UNKNOWN TO ME. CONDITIONS WERE VMC; SLIGHT HAZE ON THE HORIZON. UPON SEEING THE ACFT AT MY 12 O'CLOCK POS; I BANKED TO THE R THOUGH I BELIEVE THERE WAS SLIGHT HORIZ SEPARATION AND THE OTHER ACFT WAS IN A SLIGHT R BANK. ATC WAS VERY QUICK TO INDICATE THAT THE TFC SEPARATION PROB WAS HIS FAULT AND REPEATED THIS STATEMENT SEVERAL TIMES APPEARING TO BE APOLOGETIC.