POTENTIAL CONFLICT; DSCNT TOWARDS OCCUPIED ALT.

Narrative

AFTER SIGNING ON WITH SOUTHERN CALIFORNIA APCH; I TOLD MY FO HE HAD #1 COM. WE WERE LEVEL AT 13000 FT. I THEN GAVE THE PAX THE SAFETY BRIEFING FOR LNDG; TALKED TO COMPANY (IN RANGE CALL) AND COPIED ATIS. THE ATIS BROADCAST HAD JUST COME UP. WHILE I WAS OFF FREQ. I SAW THE FO DIAL UP 7000 FT IN THE ALT ALERTER AND BEGIN A DSCNT. I CAME ON FREQ AT ABOUT 10200 FT AND HEARD THE CTLR TELL US TO PICK OUR SPD UP TO 210 AT BAYST. I REPEATED THIS BACK. AT ABOUT 9800 FT; THE CTLR SAID TO STOP OUR DSCNT AT 10000 FT AND THEN HE SAID TO CLB BACK TO 10000 FT. WE WERE CLBING AGAIN AND DSNDED NO LOWER THAN 9600 FT. THE CTLR GAVE US A 727 TFC AT 9000 FT. WE SAID WE HAD HIM. THE CTLR SAID TO MAINTAIN VISUAL ON HIM WHICH WE DID. AFTER TALKING TO THE FO HE TOLD ME THAT HE HAD BEEN TOLD TO LEVEL OFF AT 10000 FT N AND THEN GO DOWN TO 7000 FT BUT WAS NOT CLR ON THE LEVEL OFF POINT; WE THINK IT WAS BAYST INTXN. WE WERE ON DUTY 15 HR AND 18 MIN THE DAY BEFORE. THE FO SHOULD HAVE ASKED FOR A CLARIFICATION OF THE CLRNC. SUPPLEMENTAL INFO FROM ACN 282304: WHILE THE CAPT WAS OFF THE FREQ WE WERE GIVEN A DSCNT FROM 13000 FT TO 7000 FT MAINTAIN 10000 FT TILL WHAT I THOUGHT WAS SADDE INTXN (LATER REALIZED CTLR MEANT BAYST INTXN). IF CTLR WANTS US TO ONLY DSND TO 10000 FT HE SHOULD NOT INCLUDE FURTHER CLRNC TO 7000 FT.