FLT CREW OF CL65 FORCED TO LAND ON RWY 4 AT LGA BEFORE PREVIOUS TKOF ACFT HAD BROKEN GND.

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NEW YORK LGA ARPT WAS USING RWY 4 AS THE ACTIVE WITH RWY 13/31 CLOSED FOR MAINT. WE HAD ABOUT 4 MI OF SEPARATION BTWN US AND THE ACFT AHEAD. AFTER THE ACFT AHEAD CROSSED THE LNDG THRESHOLD; LGA TWR CLRED AN ACR; MD80; INTO POS AND INSTRUCTED THEM TO BE READY FOR AN IMMEDIATE TKOF. WE DON'T LIKE THIS AS WE WERE INSIDE 3 MI AND CLOSING FAST -- VREF WAS 140 KTS. TWR CLRED THE MD80 FOR AN IMMEDIATE TKOF; BUT IT APPEARED THE CREW WAS IN NO HURRY; AS IT MUST HAVE BEEN 7-10 SECONDS BEFORE THE ACFT BEGAN TO ROLL. AS WE PASSED THE RWY THRESHOLD; THE MD80 WAS JUST BEGINNING TO ROTATE. I HELD THE ACFT OFF UNTIL MY FO TOLD ME HE WAS AIRBORNE -- AT WHICH TIME I MORE OR LESS DROPPED MY ACFT IN SO AS TO GET IT DOWN AND STOPPED. I CONTINUED LNDG FOR 2 REASONS: 1) THE TWR DID NOT CALL A GAR; AND 2) I FELT IT WAS THE SAFER OPTION TO LAND; BECAUSE HAD I ATTEMPTED A GAR AT THIS LATE POINT; WE MAY HAVE HAD A MUCH LARGER PROB MAINTAINING SEPARATION FROM THE NOW FLYING MD80. I FEEL THIS SIT COULD HAVE BEEN AVOIDED ALTOGETHER HAD THE TWR WAITED TO DEPART THE MD80 UNTIL AFTER WE HAD LANDED.