ZDC CTLR EXPERIENCED OPERROR AT FL340 WHEN DESCENDING OPPOSITE DIR TFC THROUGH OCCUPIED ALT; CORRECTIVE ACTION TOO LITTLE TOO LATE.

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I WAS WORKING R35. WILMINGTON HIGH SECTOR AT ZDC; 17 ACFT ON FREQ. I DSNDED X FROM FL350 TO FL330 -- A PHL ARR. FL330 IS A REQUIREMENT FOR PHL AND PHL SATELLITE (FL320 OR BELOW) IN THIS SECTOR. TFC SBOUND WAS Y AT FL340 -- A JAX ARR. TFC WAS NOSE-TO-NOSE; BUT THERE WAS PLENTY OF ROOM TO DSND THE PHL ARR. I COULDN'T IMMEDIATELY TURN EITHER ACFT COMFORTABLY DUE TO ADJACENT TFC AT FL350 AND FL340. THERE WAS A MODERATE AMOUNT OF COMPLEXITY IN THE SECTOR DUE TO IN-TRAIL FLOW REQUIREMENTS FOR PHL; BOS; AND MCO. THERE WERE 5 PHL ARRS IN MY TFC MIX -- 2 OF WHICH WERE ON VECTORS FOR SPACING. THERE WERE 2 BOS ARRS BOTH ON VECTORS TO ACHIEVE SPACING. THERE WERE TWO MYR ARRS ON VECTORS FROM DSCNT THROUGH TFC; BOTH ENTERED THE SECTOR AT FL340 AND NEEDED TO DSND TO FL240. X WAS ISSUED THE DSCNT CLRNC -- THE READBACK WAS PARTIALLY BLOCKED BY ANOTHER ACFT. BY THE TIME I WAS ABLE TO RE-ISSUE THE DSCNT CLRNC TO X; 21 SECONDS HAD ELAPSED. I TURNED THE SBOUND Y TO A 180 DEG HDG. I ALSO TURNED X TO THE L. I TURNED Y FURTHER TO A 160 DEG HDG. THE 21 SECONDS MADE A DIFFERENCE. I SHOULD HAVE REISSUED THE DSCNT CLRNC IMMEDIATELY INSTEAD OF TALKING TO THE OTHER ACFT; A FREQ CLARIFICATION. WE ARE SHORT STAFFED AND SPEND LONG PERIODS OF TIME ON BUSY SECTORS.