LCL CTLR AT DCA PUSHES ARRIVING ACFT FOR A HOLD SHORT COMMITMENT BECAUSE OF TFC ARRIVING ON A XING RWY. COMMITMENT IS NOT GIVEN; BOTH ACFT LAND AND SEPARATION AT THE RWY XING POINT IS 150 FT.

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OUR ACFT WAS ON VISUAL APCH TO RWY 1 AT DCA AT THE SAME TIME A DHC8 WAS ON VISUAL APCH TO RWY 33. WE WERE FOLLOWING AN ACFT 3 MI AHEAD SO SLOWED TO 150 KTS AT 5-6 MI. THE DASH 8 THEN HAD A 40 KT SPD ADVANTAGE. WE WERE SEQUENCED TO LAND AHEAD OF THE DASH 8. WE WERE CLRED TO LAND AND TWR ADVISED US TO 'ADVISE IF ABLE TO HOLD SHORT RWY 33.' NOT WANTING TO COMMIT TO AN UNPLANNED LAHSO FOR OPERATIONAL REASONS; CAPT ROGERED THE REQUEST WITH NO INTENTION OF LAHSO CONFIRMATION. THE DASH 8 WAS ON A COLLISION COURSE WITH US; CONSTANT BEARING; DECREASING RANGE. WE WERE CLRED TO LAND RWY 1. CAPT SET THE AUTOBRAKE TO '3' INSTEAD OF '2' TO ASSIST IN STOPPING IN A SHORTER DISTANCE. WE TOUCHED DOWN NORMALLY AND ON ROLLOUT; TWR AGAIN ASKED US TO 'ADVISE ABLE TO HOLD SHORT RWY 33.' CAPT DID NOT CONFIRM OUR FLT TO LAHSO. THE FO HEARD 'HOLD SHORT RWY 33' BECAUSE THE TWR CTLR KEYED THE MIKE AS HE STARTED TO TALK AND THE FIRST WORD; 'ADVISE;' WAS HARD TO UNDERSTAND. AS WE SLOWED TO 60 KTS AND CAPT TOOK THE ACFT; WE TOLD TWR WE COULD HOLD SHORT; AND MADE A L TURNOFF ONTO TXWY N. WITHIN A FEW SHORT SECONDS; THE DASH 8 CROSSED RWY 1; ABOUT 150-200 FT AWAY FROM US.