A320 FLC TERRIFIED WHEN THE CAPT OBSERVED A LIGHT TWIN CARGO ACFT ON SHORT FINAL ON AN INTERSECTING RWY TO THE ONE ON WHICH THEY WERE MAKING THEIR TKOF ROLL.

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WE WERE IN POS AND HOLDING ON RWY 1 AT DCA. WHILE IN POS; WE OBSERVED A SMALL TWIN ACFT WITH THE LNDG GEAR DOWN MAKING A SHARP R TURN AT APPROX 500 FT AGL AND BREAKING OFF THE LNDG APCH TO RWY 33. SHORTLY AFTER THE TURN WAS OBSERVED; WE WERE CLRED FOR TKOF. THIS TKOF WAS A COMPLEX OP WITH AN IMMEDIATE L TURN REQUIRED TO PREVENT OVERFLT OF THE DCA PROHIBITED AREA. THE FO WAS FLYING AND AFTER TKOF CLRNC WAS ACKNOWLEDGED ADVANCED THRUST TO TOGA. AS I COMPLETED MY INSPECTION OF THE EQUIP INSTS I OBSERVED THE SMALL TWIN IN THE R WINDOW JUST BEHIND THE FO'S HEAD. A COLLISION SEEMED IMMINENT; SO I ABORTED THE TKOF AT APPROX 40-50 KTS. FOLLOWED COMPANY SOP AND CLRED THE ACTIVE RWY. ADVISED TWR WE WERE REQUESTING NEAR MIDAIR RPT FROM ATC (THE TWR LATER SAID THERE WAS NO CONFLICT IN THEIR OPINION). THE FO AND MYSELF FELT THIS EVENT WAS AS CLOSE A CALL AS EITHER OF US HAVE HAD IN OUR COMBINED 43000 HRS OF FLYING. THE PROB IS THE RESULT OF TRYING TO SQUEEZE TOO MUCH FLYING INTO TOO SMALL A TIME PERIOD/SPACE.