ACR MLG FLC UNABLE TO ACCEPT AMENDED ALT ASSIGNMENT CLRNC ACCOUNT TCASII RA.

Narrative

WE WERE ON A 240 DEG RADAR VECTOR HDG TO INTERCEPT SFO 095 DEG RADIAL DSNDING OUT OF 8300 FT FOR OUR CLRED ALT OF 8000. ATC ISSUED VFR TFC AT 1 O'CLOCK 3 MI A FEW MOMENTS LATER WE RECEIVED A 'TA' WARNING. I RINGED THE TCASII DOWN TO 5 MI SCALE AND OBSERVED THE TARGET AT 1 O'CLOCK; 3 MI; 1300 FT BELOW US AND CLBING. ATC ISSUED A 10 DEG L TURN TO INTERCEPT SFO 095 DEG RADIAL. AS WE TURNED THE TARGET BECAME A RA. THE TARGET WAS AT 1 O'CLOCK; 400 FT BELOW US; CONVERGING TO WITHIN 1/2 TO 3/4 OF A MI. WHILE RESPONDING TO THE RA; THE CTLR ISSUED A CLRNC TO 7000 FT. I ADVISED THE CTLR WE WERE UNABLE TO ACCEPT THE CLRNC AS WE WERE RESPONDING TO A 'RA'. THE CTLR SAID HE WOULD NOTE THAT WE COULDN'T ACCEPT THE CLRNC. WITHIN 5 SECONDS THE TARGET CLRED TO OUR R AND REAR. I ADVISED ATC WE COULD NOT ACCEPT A DSCNT. WE WERE CLRED TO 7000 AND GIVEN A FREQ CHANGE. WE PROCEEDED TO SFO. THE LENGTH OF TIME FROM 'TA' TO 'CLR OF CONFLICT' WAS 25-30 SECONDS. THE TIME DURING WHICH WE WERE UNABLE TO ACCEPT THE DSCNT CLRNC WAS ABOUT 5 SECONDS. SINCE WE WERE STILL N OF THE SFO 090 DEG RADIAL AT 21 MI WE HAD NOT ENTERED THE SFO TCA. THUS; NO COMS WAS REQUIRED OF THE VFR TFC. HIS RAPID CLB AND CLOSURE TO WITHIN 400 FT SET OFF THE TCASII RESOLUTION. OUR LOCATION AND ALT WAS NOT A 'HEALTHY' PLACE FOR A VFR ACFT TO CROSS THE ARR STREAM OF ACFT FOR SFO.