A B757-200 FLT CREW MISTOOK A HOTEL'S RED LIGHTS FOR THE VASI DURING A LOW VIS NON PRECISION APCH TO RWY 31 AT LGA. THE CREW ALSO RECEIVED A GPWS PULL UP ALERT.

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I HAD A SIT THAT REALLY CONCERNED ME DURING THE LOC APCH TO RWY 31 AT LGA LAST NIGHT. THE WX KEPT GOING IN AND OUT OF MINIMUMS; AND AN ACR Y FLT HAD GONE AROUND; BUT 3 OTHER AIRPLANES LANDED AFTER HIM. THE ACR Y FLT HAD REQUESTED A CHANGE TO RWY 4; BUT WAS DENIED BY APCH CTL. BIG DIFFERENCE ON THE VISIBILITY RPTED BY ATIS VS TWR. AT ONE POINT THE ATIS RPTED VIS AT 1 MI; BUT TWR RPTED 2.5 MILES. BY THE TIME WE TURNED TO FINAL APCH; LGA TWR RPTED VIS AT 1.75 NM; REQUIRED VIS FOR THE LOC APCH IS 1.5 NM. WE SET A DA OF 650 FT FOR THE CONSTANT DESCENT APCH PROC APP; AND WHEN THE FO CALLED APCHING DA; WE BOTH LOOKED OUTSIDE AND SAW WHAT LOOKED LIKE RED LIGHTS FOR THE VASI FOR RWY 31. VISIBILITY WAS MARGINAL; BUT WE BOTH THOUGHT WE HAD THE RWY ENVIRONMENT IN SIGHT. AS WE GOT CLOSER (AND THIS HAPPENED PRETTY FAST); WE REALIZED THAT THE VASI WAS ACTUALLY FARTHER DOWN; AND WHAT WE WERE INITIALLY LOOKING AT WAS ACTUALLY THE RED LIGHTS ON TOP OF THE SHERATON HOTEL; WHICH IS PERFECTLY LINED UP ON FINAL APCH TO RWY 31. AT THE SAME TIME WE GOT AN 'OBSTACLE AHEAD; PULL UP' FROM GPWS. I IMMEDIATELY ADDED POWER AND PULLED UP TO STOP THE WARNING. WE COULD BOTH SEE THE TOP OF THE BUILDING; AND THE RWY. SINCE THE WARNING STOPPED; AND WE WERE STILL IN A POSITION TO LAND; WE CONTINUED THE APCH TO AN UNEVENTFUL LNDG. WE ESTIMATED VISIBILITY TO BE RIGHT AT MINIMUMS; WITH WINDS 010 AT 13 KTS. WE SET AN INITIAL V/S OF 700 FPM; AND LATER INCREASED IT TO 800 FPM. WITH THESE CONDITIONS; AN ILS TO RWY 4 WOULD HAVE BEEN MORE PRUDENT; IF NOT SAFER. AS A MINIMUM; I ADVOCATE FOR A NOTE IN THE APCH PLATE FOR THE LOC RWY 31 ABOUT THE SHERATON HOTEL AND ITS RED LIGHTS ON TOP. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: BOTH PLTS INTERPRETED THE HOTEL LIGHTS AS VASI LIGHTS. AFTER RESPONDING TO THE GPWS WARNING; THEY SAW THE VASI LIGHTS FURTHER DOWN THE RWY. THE CAPT THINKS THERE SHOULD BE A WARNING ON THE APCH PLATE. SUPPLEMENTAL INFO FROM ACN 641633: DURING LOC RWY 31 APCH TO LGA; I WAS THE NON-FLYING PLT AND AT DECISION ALT I CALLED LIGHTS IN SIGHT. I HAD OBSERVED RED LIGHTS SLIGHTLY L OF OUR COURSE AND THOUGHT THEM TO BE VASI'S. A SPLIT SECOND LATER I REALIZED THAT THEY WERE NOT THE VASI'S; BUT LIGHTS ON THE SIDE OF THE BUILDING. AT THE SAME TIME LOOKING FURTHER INTO THE DISTANCE; I COULD SEE THE ACTUAL VASI'S. WITHIN SECONDS OF SPOTTING THE REAL VASI'S; THE ENHANCED GPWS SOUNDED; 'PULL UP OBSTACLE.' SINCE WE WERE VMC AT THIS POINT; WE CONTINUED THE APCH; BECAUSE WE COULD SEE THE RWY AND THE BUILDING THAT WAS CAUSING THE GPWS TO SOUND. AT NO TIME WAS THE FLT UNSAFE; HOWEVER; I BELIEVE CREWS SHOULD BE CAUTIONED ON THIS APCH THAT LIGHTS ON A BUILDING COULD BE MISTAKEN FOR RWY ENVIRONMENT. I SHOULD MENTION THAT AS WE WERE APCHING DECISION HEIGHT; I WAS SLIGHTLY DISTRACTED WHEN TWR USED OUR CALL SIGN FOR THE ACFT THAT WAS CLRING THE RWY IN FRONT OF US WHILE GIVING THEM TAXI INSTRUCTIONS. CALLBACK CONVERSATION WITH RPTR ACN 641633 REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE VISUAL INTERFERENCES ARE RED AND WHITE LIGHTS ATOP THE SHERATON HOTEL IN FLUSHING; NY. ON THE DAY IN QUESTION THE ARPT HAD ALSO GIVEN ILS APCHES TO RWY 4 BUT SWITCHED BACK TO RWY 31. ANOTHER ACR HAD CONDUCTED A GO AROUND TO RWY 31 PRIOR TO THE CREW'S APCH. THE RPTR QUESTIONS WHY THE TWR WAS NOT GIVING PRECISION APCHES IN LOW VISIBILITY AND SNOW.