CAPT OF AN ACR MLG REFUSED TO ABORT TKOF WHEN INSTRUCTED BY TWR.

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TWR CLRED US INTO POS ON RWY 18 AND ADVISED 'BE READY FOR IMMEDIATE AS SOON AS TFC CLRS.' I BEGAN SPOOLING THE ENGS. TKOF CLRNC INCLUDED THE REMARK THAT TFC WAS ON 2 MI FINAL; AND THAT WE SHOULD GO OR CLR THE RWY. AFTER PWR WAS SET AND AUTOTHROTTLE SHOWED 'THROTTLE HOLD' -- TWR SAID 'CANCEL TKOF CLRNC AND TURN R AT RWY 15.' FOR A COUPLE OF SECONDS I WENT THROUGH THE DECISION FREQ/RECOGNITION TIMEOUT PROCESS AND BY THE TIME I HAD GOTTEN THE INSTRUCTION STRAIGHT IN MY HEAD WE WERE WELL ESTABLISHED AT 100 KTS IN THE TKOF ROLL. TWR MADE 3 CALLS TO US DURING THE REMAINDER OF THE ROLL; BUT WE DID NOT ANSWER UNTIL AIRBORNE AND OUT AT 500 FT. OUR TRAINING EMPHASIZES NOT ABORTING ONCE THE PWR IS SET EXCEPT FOR SERIOUS; EMER TYPE PROBS. I AM EXTREMELY RELUCTANT TO ABORT TKOF FOR TFC SEQUENCING. THIS IS THE FIRST TIME IN 22 YEARS I HAVE EVER BEEN ASKED TO ABORT TO SOLVE A TFC SEQUENCE PROB. NATIONAL ARPT IS DANGEROUS ENOUGH WITHOUT ATTEMPTING TO SHOEHORN MORE TFC THAN IT WILL HOLD. WE COULD HAVE HELD FOR 45 MORE SECONDS (IN FACT GLADLY WOULD HAVE HELD) TO INSURE ADEQUATE CLRNC. HAVING MADE THE INITIAL MISTAKE OF CLRING US FOR TKOF; THE CORRECT SOLUTION FOR THE CTLR WOULD HAVE BEEN A GAR FOR INBOUND TFC WITH INSTRUCTIONS TO MAINTAIN VISUAL CLRNC -- NOT AN ATTEMPT TO EXPEDITE US OFF THE RWY BY DEMANDING AN ABORT AND AN IMMEDIATE RWY CLRNC.