ACR PIC OF MLG PERFORMS GAR PROC ON THE STRENGTH OF A TCASII RA ON SHORT FINAL WITH OTHER ARR TFC IN SIGHT.

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WE HAD RECEIVED NUMEROUS TFC CALLOUTS FROM THE TWR WHILE ON FINAL TO RWY 30L. AT ABOUT 1200 FT I WAS MONITORING A LIGHT ACFT AT OUR 10 O'CLOCK; WHO HAD TURNED ONTO L BASE FOR RWY 29. HE WAS IN A LOW; CLOSE PATTERN FOR THAT RWY; WHICH IS TYPICAL; BUT MY DISTR TO ASSURE MYSELF OF HIS TIME BASE-TO-FINAL TURN CONTRIBUTED TO MY FORGETTING TO DEACTIVATE THE RA FUNCTION OF OUR TCASII BY 1000 FT; WHICH IS OUR (COMPANY) PROC. I WAS UNABLE TO DETERMINE WITH CONFIDENCE THAT THE TCASII CLB COMMAND; WHICH OCCURRED A COUPLE OF SECONDS LATER; WAS TRIGGERED BY THAT ACFT; HIS POSSIBLE TURN OVERSHOT (THE RWY CTRLINE ARE ABOUT 750 FT APART); OR ANOTHER ACFT. I INITIATED A GAR; AND WE WERE TURNED ONTO A R DOWNWIND AND LANDED ABOUT 8 MINS LATER. HAD TCASII BEEN TURNED TO A 'TA ONLY' PRIOR TO 1000 FT; THE GAR PROBABLY WOULD NOT HAVE APPEARED ADVISABLE. OUR ADDITIONAL EXPOSURE TIME IN A HIGH DENSITY TFC PATTERN CERTAINLY WASN'T DESIRABLE. MY FORGETFULNESS NOTWITHSTANDING; A PROCEDURAL CHANGE TO TURN OFF THE RA FUNCTION EARLIER THAN AT 1000 FT MIGHT BETTER DISTRIBUTE COCKPIT WORKLOAD AT A PEAK TIME.