B747 HAD NMAC WITH A DC10 ON THE PARALLEL VISUAL APCH AT SFO RWYS 28L AND 28R.

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WE WERE ON APCH TO SFO RWY 28L. FROM 7000 FT WE WERE GIVEN INSTRUCTIONS TO DSND TO 3000 FT AND SLOW TO 180 KTS. I RECALL THE COPLT ADVISING THE CAPT WHO WAS FLYING; TO SLOW DOWN. THE CAPT ANSWERED THAT HE COULD NOT GO DOWN AND SLOW AT THE SAME TIME. THE ACR Y DC10 CAME FROM WOODSIDE AT 4000 FT AND CROSSED FROM L TO R BELOW US. ONCE HE WAS PAST US WE WERE DIRECTED TO DSND TO 3000 FT. WE WERE CLRED FOR THE APCH RWY 28L AND ADVISED THAT THERE WAS A DC10 APCHING ON RWY 28R. MY FIRST RECOLLECTION OF ACR Y WAS WHEN WE CAME UP EXACTLY ABREAST OF HIM. THE CAPT ASKED US TO KEEP HIM IN SIGHT. AT THAT POINT WE RECEIVED A TA ON THE TCASII. I STARTED TO WATCH HIM CLOSELY AND OBSERVED HIM MAKING CORRECTIONS IN OUR DIRECTIONS. BY THIS TIME WE HAD SLOWED TO APCH SPD; CONFIGURED FOR LNDG AND FINAL CHK COMPLETE. AS ACR Y CONTINUED SLIDING TOWARD US WE MOVED L OF CTRLINE TO GIVE HIM ROOM. AT THE NEAREST POINT I WOULD ESTIMATE HIS PROX AT 200 FT TO 300 FT AT OUR ALT (APPROX 1200 FT). WE THEN RECEIVED AN RA TO DSND. IN COMPLYING WITH THE RA WE DSNDED CONSIDERABLY BELOW AND SLOWED TO 10 KTS BELOW APCH SPD. WE HAD ALSO MOVED A GOOD 1/2 MI S OF CTRLINE. IT APPEARED THAT ACR Y HAD LINED UP ON RWY 28L. WHILE WE WERE COMPLYING WITH THE RA; ACR Y BEGAN TO MOVE R AND ACCELERATED AHEAD OF US. WE WERE STABILIZED BY 500 FT. AFTER WE ACHIEVED PROPER SPACING; WE REACQUIRED CTRLINE AND GS. THE LNDG WAS UNEVENTFUL. WE DID NOT ADVISE TWR THAT WE HAD AN RA -- TOO BUSY. WE RECEIVED NO COM FROM TWR DURING THE ENTIRE EPISODE. THERE WAS ALSO NO COM FROM ACR Y.