A B752 CREW ON APCH TO SMF TOOK EVASIVE ACTION TO AVOID A LIGHT ACFT.

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ON A 250 DEG HDG; VECTORS FOR VISUAL RWY 16L SMF; DSNDING FROM 5000 FT TO 2000 FT. ATC CALLED TFC 'TFC 2 O'CLOCK POS; TYPE/ALT UNKNOWN.' WE WERE APPROX 3000-3500 FT. NOTHING ON TCASII. WE BOTH LOOKED (INTO SUN). FO POINTED L AND STATED; 'SKIPPER; WE HAVE TO TURN L NOW.' I DISCONNECTED THE AUTOPLT AND TURNED L; STILL DSNDING. GLANCING AT TCASII; I SAW NOTHING. NOW; R WING HIGH; I COULD SEE THE TFC OUT THE COPLT'S WINDOW. I CONCLUDED THE TURN ALONE WOULD NOT CLR THE CONFLICT. I DISCONNECTED THE AUTOTHROTTLES AND STARTED A 2000 FPM CLB. APPROX 2-3 SECONDS LATER; WE GOT A POP-UP RA TO CLB. GREEN ARC AT 2500 FPM; I FLEW TO IT. TCASII SHOWED AN ACFT 400 FT DIRECTLY BELOW US. WE LEVELED AT 4000 FT MSL. CONTINUED FOR A PERFECT AND UNEVENTFUL LNDG. ATC STATED THEY WERE TALKING TO THE ACFT ON ANOTHER FREQ. THEY JUST GAVE HIM A SQUAWK; BUT HAD NOT RADAR IDENTED HIM YET. I BELIEVE HE/SHE WAS HEADS DOWN PUTTING IN THE SQUAWK AND NOTICED THEIR XPONDER WAS NOT ON. THIS WOULD EXPLAIN THE LAST SECOND POP-UP RA. ACFT SEEMED VERY CLOSE IN TO NOT BE IN RADAR CONTACT. FOR SOME REASON ON THE RWY 16L FINAL APCH.