ARTCC RADAR CTL TEAM ARE MADE AWARE OF CONFLICT BTWN AN MD80 AND B727 BY CONFLICT ALERT FUNCTION. ACTIONS WERE NOT TIMELY OR SUFFICIENT TO STOP THE ERROR.

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I WAS THE L-SIDE AT A BUSY SECTOR. WE WERE WORKING AN INCREASED VOLUME OF TFC DUE TO WX BTWN PITTSBURGH AND ERIE; PA. ACFT WERE COMING BROADSIDE INTO THE SECTOR AT EVERY ALT IN CONFLICT WITH ALL OUR NORMAL TFC FLOWS COMING UP FROM THE S. IN ADDITION WE WERE REQUIRED TO PROVIDE 20 MI IN TRAIL ON THE EWR FLOW; WHICH HAD DOUBLED WITH THE RERTES FROM THE W. AT THE TIME OF THE ERROR SEVERAL ACFT HAD BEEN CLRED INTO HOLDING AT HPW. ACFT X WAS FLYING RIC J14 PXT AT FL310; ACFT Y HAD BEEN DSNDED 3 MINS PRIOR FROM FL330 TO FL290; TO HOLD UNDERNEATH THE TFC. DUE TO OTHER ACTIVITY IN THE SECTOR; WE FAILED TO SEE THE SUBSTANDARD DSCNT RATE OF ACFT Y. HE DSNDED ONLY 2300 FT IN 3 MINS. WHEN WE SAW THE CONVERGING ACFT; THERE WAS 1000-1700 FT LEFT IN THE ACFT Y DSCNT AND THEY WERE HEAD-ON. CONFLICT ALERT ACTIVATED AFTER WE SAW THE SIT; THE MD80 GOT AN RA AND CLBED 300 FT. THE B727 TOOK AN ADDITIONAL FULL MIN TO GO THE LAST 1000 FT IN SPITE OF AN EXPEDITED REQUEST. IN MY OPINION; TFC VOLUME AND COMPLEXITY WERE PARTLY TO BLAME; AS WAS THE EXTREMELY SLOW DSCNT RATE OF THE B727 -- EVEN AFTER AN IMMEDIATE; EXPEDITED DSCNT CLRNC WAS ISSUED. VECTORS WERE NOT AN OPTION AT THAT POINT. HOW COULD IT HAVE BEEN PREVENTED? BETTER DSCNT BY THE B727; MORE AWARENESS ON PART OF RADAR TEAM; RELAXATION OF 20 MI IN TRAIL EWR RESTR.