POTENTIAL CONFLICT WHEN A DSNDING MD80 DOES NOT GET A TA; BUT IS CLRED THROUGH THE ALT OF A CIRCLING CPR CITATION JET VFR AT 17500 FT; 65 MI NE OF SMF; CA.

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LOCATION: APPROX 65 NM ENE OF SMF ON FLUNK ARR. DSNDING THROUGH FL180 CLRED TO 16000 FT; I NOTICED A TCASII CONTACT DIRECTLY AHEAD ABOUT 5 NM; 900 FT BELOW. I ASKED SMF APCH CTL IF THEY HAD THE CONTACT AND THE CTLR SAID 'YES; VFR AT 17500 FT.' JUST THEN; WE RECEIVED A TCASII ALERT ADVISING US TO MONITOR VERT SPD AND THE VSI INSTRUCTED US TO LEVEL OFF. WE DID SO AND THEN WE GOT ANOTHER IMMEDIATE ALERT TO CLB -- WE COMPLIED. I PICKED UP THE CONTACT VISUALLY AT ABOUT 3 NM IN A R TURN AND IT PASSED LESS THAN 2 NM OFF OUR L WING APPROX 500 FT BELOW. AT THIS TIME WE WERE AT FL185 AND THE TCASII ALERT STOPPED. THE OTHER ACFT APPEARED TO BE A CITATION JET. WHEN I TOLD THE CTLR THAT WE HAD AN RA AND THE OTHER ACFT WAS MUCH CLOSER THAN WE WOULD LIKE; HE RESPONDED THAT HE WAS NOT TALKING TO THE OTHER ACFT AND THEY MAY HAVE HAD THEIR ALTIMETERS MISSET. MY CONCERN IS THAT WE WERE CLRED THROUGH THE OTHER ACFT'S VFR ALT AND IF NOT FOR TCASII WE MAY HAVE NEVER SEEN THE OTHER ACFT. AT NO TIME WERE WE FOREWARNED THAT THIS ACFT WAS IN THE VICINITY. WHEN I QUESTIONED THE CTLR; HE DID NOT APPEAR TO BE THE LEAST BIT CONCERNED.