LGT HAS NMAC WITH CUSTOMS ACFT WHILE ON ARR RTE.

Narrative

ON APCH TO SAN ON BARET 4 ARR AND DSNDING THROUGH APPROX 13000 FT; SAW A BIZJET AT 1:30 O'CLOCK POS IN STEEP L TURN COMING AT US AT OUR ALT. TFC PASSED ON OUR R GOING IN OPPOSITE DIRECTION. ESTIMATE DISTANCE AT 300-500 FT HORIZLY. FO WAS AT CTLS WITH AUTOPLT ON AND WE TOOK NO EVASIVE ACTION. THERE WAS NO TIME. OUR HDG WAS APPROX 255 DEGS MAGNETIC AND CONFLICTING TFC APPEARED OUT OF THE SETTING SUN. TFC APPEARED TO BE IN A 60-70 DEG L BANK TO AVOID COLLISION. WE HAD NO ATC ADVISORY AND OUR TCASII WAS INOP. ZLA CTLR ANSWERED MY RPT OF A NEAR MISS BY SAYING RADAR COVERAGE WAS POOR IN THAT AREA AND THE ACFT WAS PROBABLY A UNITED STATES CUSTOMS BIZJET MANEUVERING IN THAT AREA. WHEN ON GND I CONTACTED ZLA SUPVR AND GAVE HER AN ORAL RPT OF OUR NEAR MISS. SHE FOLLOWED UP WITH 2 CALLS TO MY HOTEL CONFIRMING THE SUBJECT ACFT WAS A UNITED STATES CUSTOMS CESSNA CITATION AND LATER THAT SHE HAD TALKED TO THE PLT WHO APPARENTLY ADMITTED A CLOSE ENCOUNTER. CTR SUPVR ALSO INDICATED THAT THE CITATION WAS ON A DISCRETE XPONDER CODE; BUT WAS NOT KNOWN OR SEEN BY THE ATC CTLR. I AM AWARE OF THE IMPORTANCE OF CATCHING SMUGGLERS BUT WE CANNOT AFFORD A MIDAIR WITH ANY ACFT. I AM GRATEFUL THE CITATION PLT SAW US IN TIME TO REACT (WE HAD LNDG LIGHTS ON) AND I HOPE SOME MEASURES CAN BE TAKEN TO COORDINATE CUSTOMS FLTS WITH ATC FOR POSITIVE RADAR SEPARATION. THIS INCIDENT TOOK PLACE ON A PUBLISHED ARR! AS TO OUR ROLE; IT WAS TOO LATE TO EVADE DUE TO THE LATE VISUAL CONTACT CAUSED BY THE GLARE OF THE SETTING SUN. THERE MUST BE SOME BETTER WAY OF CTLING THESE BORDER FLTS INTO CTLED AIRSPACE.