APCH CTLR RECEIVED CONFLICT ALERT ON 2 ACR ACFT DURING VECTORS FOR ILS APCH RESULTING IN THE CTLR INSTRUCTING EACH ACFT TO TURN AND THE RPTR TO CLB. THE RPTR MADE A 60 DEG BANK TO ASSURE SEPARATION DUE TO THE URGENCY OF THE CTLR'S VOICE. BOTH ACFT WERE IN IMC.

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WE WERE BEING VECTORED FOR AN ILS APCH TO RWY 4 AT LGA. WE WERE IMC; LEVEL AT 2700 FT MSL; ABOUT 10-15 NM SW OF THE ARPT. LGA APCH CTL WAS VERY BUSY; AND WE HAD ALREADY HEARD THE CTLR TELL 2 DIFFERENT ACFT TO BREAK OFF THEIR APCHS BECAUSE OF TOO TIGHT SPACING; TO BE VECTORED BACK AROUND FOR ANOTHER APCH. ALL OF A SUDDEN; THE CTLR CALLED US; IN A VOICE ABOUT 3 OCTAVES HIGHER THAN NORMAL; TO 'TURN R IMMEDIATELY TO 090 DEG HDG' (ABOUT A 90 DEG TURN) FOLLOWED BY 'AND CLB TO 4000 FT' (IN AN EQUALLY URGENT/PANICKY TONE). AT THE SAME TIME; HE WAS ISSUING TURN INSTRUCTIONS TO AN ACR Y FLT. BECAUSE OF THE PANICKY TONE OF HIS VOICE; I ACTUALLY PERCEIVED THAT A MIDAIR COLLISION MAY BE IMMINENT; SO I DISCONNECTED THE AUTOPLT AND ROLLED INTO A 50-60 DEG BANK; IN AN 'ESCAPE' MANEUVER. (OUR TCASII NEVER GAVE US AN ALERT; BUT THERE WAS NO TIME TO DETERMINE IF IT WAS OPERATING PROPERLY.) WE WERE IMC THE WHOLE TIME; AND FOR A PERIOD OF AT BEST 8-10 SECONDS; WE WEREN'T SURE IF ANOTHER ACFT WOULD APPEAR ACROSS OUR WINDSCREEN. I THEN ASKED IF WE WERE CLR OF TFC; AND HE SAID THAT WE WERE; AND THAT WE HAD NEVER BEEN CLOSER THAN 2 - 2 1/2 NM LATERAL SEPARATION; BUT THAT WE WERE AT THE SAME ALT. I SPOKE WITH NEW YORK TRACON SUPVR ON THE GND LATER; AND HE CONFIRMED THAT IT HAD BEEN HIS CTLR'S ERROR. I TOLD ATC SUPVR THAT IT WOULD HAVE GREATLY HELPED OUR PERCEPTION OF THE SIT IF THE CTLR HAD SOMEHOW BEEN ABLE TO COMMUNICATE THAT A COLLISION WAS NOT IMMINENT; BECAUSE ROLLING INTO A 60 DEG BANK COULD POTENTIALLY HAVE CAUSED PROBS OF ITS OWN. HE AGREED THAT THAT WOULD HAVE BEEN HELPFUL; AND ADDED THAT THEY HAD RECEIVED 2 CONFLICT ALERTS AT THEIR TRACON. HE SAID THE 2 PLANES WERE AT THE SAME ALT; BUT NEVER GOT CLOSER THAN 2 1/2 NM APART.