OPERROR LTSS BTWN AN ACR B737 AND WESTWIND WHEN THE ACR DSNDED FROM AND CONFLICTED WITH THE WESTWIND.

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WE WERE BEING VECTORED TO A DOWNWIND FOR RWY 27R AT PHL. AIRSPD WAS 210 KTS; 6000 FT. TFC SEEMED ABOUT NORMAL; NOT TOO MUCH FOR PHL. WE WERE CLRED TO LEAVE 6000 FT AND DSND TO 3000 FT. I RESPONDED AND WE BEGAN OUR DSCNT ON AUTOPLT. THERE WERE A FEW TARGETS ON TCASII BUT NONE WERE OF CONCERN TO THE TCASII. AT 5700 FT WE RECEIVED AN RA TO CLB. CAPT RESPONDED BY DISCONNECTING AUTOPLT AND CLBING. AS THIS WAS HAPPENING; ATC TOLD US TO CLB TO 6000 FT. WE SAW WESTWIND ON TCASII ONLY; NEVER VISUALLY. CAPT TALKED TO APCH ON PHONE AND CTLR ADMITTED IT WAS A BAD CLRNC ON THEIR PART. CAPT SAID FROM WHAT WE COULD SEE ON TCASII IT LOOKED VERY CLOSE HAD WE CONTINUED DSCNT. CTLR SAID THEY WERE PRETTY SURE IT WOULD HAVE BEEN A HIT. I HAVE HAD TO RESPOND TO SEVERAL RA'S OVER THE PAST FEW YRS; THIS IS THE FIRST ONE THAT WAS A LIFE SAVER. THE CTLR SAID HE DID MAKE THE BAD CALL; BUT IN HIS OWN DEFENSE HE SAID HE THEN TOLD US TO CLB. WHAT IF WE HAD MISSED THE CALL OR THERE HAD BEEN A STUCK MIKE ON THE FREQ? TCASII IS WORTH ITS WT IN GOLD.