OPERROR LOSS OF SEPARATION BTWN ACR X AND UGA Y ON CONVERGING COURSE WITH UGA Y CLBING TO THE SAME ALT AS ACR X.

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FLYING THE NEWARK 4 SID; OUR CLRNC WAS DIRECT SAX; SAX 311 DEG RADIAL COATE INTXN ON COURSE; CLRED ALT 10000 FT; ATC CALLED TFC A KING AIR R TO L CLBING TO 10000 FT. WE ACKNOWLEDGED THAT WE WERE LOOKING FOR THE TFC. SHORTLY THEREAFTER OUR TCASII SOUNDED A RA; 'CLB; CLB.' WE CLBED TO 10500 FT AND THE ADVISORY STOPPED. I OBSERVED THE KING AIR ON TCASII AT 9700 FT AND SHORTLY THEREAFTER SAW THE KING AIR OUT THE L SIDE. THE KING AIR HAD PASSED DIRECTLY UNDER US; HAD WE BOTH BEEN AT 10000 FT WE WOULD HAVE COLLIDED. I NOTIFIED ATC THAT WE HAD RESPONDED TO AN RA AND WE STARTED TO RETURN TO 10000 FT. WE WERE SUBSEQUENTLY ASSIGNED A FREQ CHANGE AND ASSIGNED A NEW HIGHER ALT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR WAS ASKED IF THE CTLR GAVE ANY INDICATION AS TO WHETHER THE KING AIR WAS VFR OR IFR WHEN THE TFC WAS ISSUED. HE ANSWERED NO BUT INDICATED THAT AFTER THE TFC WAS ISSUED HE MENTIONED TO THE CTLR THAT THEY WERE AT 10000 FT. RPTR INDICATED THAT THE CTLR DID NOT REPLY AND ALSO INDICATED THAT THE FREQ WAS NOT BUSY.