ACR HAS NMAC WITH SMT ON VECTORS TO APCH.

Narrative

ACFT HAD RECEIVED VECTOR OF 270 DEG OFF THE KAYOH 2 ARR. VISIBILITY AT SNA WAS RPTED AS 5 HAZE. THE REDUCTION IN VISIBILITY MAY HAVE BEEN LOWER AS LCL CONDITIONS VARY IN THE LOS ANGELES BASIN. WE WERE VECTORED ACROSS THE INBOUND LOC APCH FOR RWY 19R. AN MLG WAS POINTED OUT AS TFC EBOUND BEING VECTORED AHEAD OF US. MANY TARGETS WERE INDICATED ON THE TCASII. WE WERE DIRECTED TO TURN R TO 300 DEG AND REMAIN LEVEL AT 5000 FT. THE TCASII IMMEDIATELY SHOWED A 'TA' AHEAD AND TO THE L; LOW AND CLBING. APCH ISSUED A FURTHER TURN TO R. THE TURN WAS INCREASED SLIGHTLY TO AVOID THE POSSIBLE CONFLICT. COAST APCH ISSUED A TA FOR AN SMT BELOW AND TO THE L. THE TCASII ISSUED A 'RA'. THE CAPT ORDERED IMMEDIATE EVASIVE ACTION. I BANK FURTHER R TO APPROX 45 DEG AND LOWERED THE NOSE AS WE SHARPLY REDUCED PWR. THE 'RA' ON TCASII TERMINATED AND THE DSCNT WAS ARRESTED AT APPROX 4200 FT. NO INJURIES WERE RPTED. ISSUES: THE CTLR ISSUED HIS TA MUCH TOO LATE IN THE SEQUENCE TO REASONABLY AVOID THE CONFLICT/NEAR MISS. ARR VECTORS INTO SNA ARE HABITUALLY TOO CONVOLUTED AND LENGTHY. EXCESSIVE MANEUVERING IN CROWDED AIRSPACE ONLY INCREASES EXPOSURE TO POSSIBLE TFC CONFLICT. TCASII PLAYED A DEFINITE ROLE IN AVOIDING A NMAC.