MIL FLT CREW TOOK CLRNC MEANT FOR ANOTHER MIL ACFT AND DESCENDED TO WRONG ALT.

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I BELIEVE THE ROOT CAUSE OF THIS INCIDENT TO BE THE CURRENTLY UNSATISFACTORY STAFFING LEVEL AT COAST TRACON. ACCORDING TO A RECENT LECTURE BY AN FAA REP AT MCAS EL TORO DURING A WING SAFETY STAND DOWN; COAST TRACON HAS ABOUT 50% OF THE CTLRS REQUIRED. THIS CTLR WAS BUSY! ADD A FEW EQUIP PROBS TO A SYS ALREADY OVERLOADED AND THE PROBABILITY OF HAZARD DETECTION AND ELIMINATION DROPS TO ZERO. OBVIOUS FIX? MORE PEOPLE; MORE SCOPES; BETTER EQUIP; AND ALL IN A TIMELY MANNER. WE WERE GIVEN A DES FROM FL240 TO 12000' ABOUT 25 MI E OF OCN; AND WHEN 10 MI E AT 12000' WE WERE TOLD BY CENTER TO SWITCH TO COAST APCH ON 380.2. I CHKED IN WITH INFO FOXTROT AT 12000'; ALTIMETER SETTING WAS 30.09. THE CTLR THANKED US FOR FOXTROT AND ASKED OUR INTENTIONS. I REPLIED THAT WE WANTED A PAR TO A FULL STOP. WE WERE THEN TOLD TO DEPART OCN HDG 260 DEGS AND DES TO 10000'. I ROGERED AND BEGAN OUR DES TO 10000'. THE CTLR SEEMED TO BE QUITE BUSY AND A HURRIED CALL WAS GIVEN TO DES TO 9000' AND SWITCH 337.2 (FREQ POSSIBLY COULD HAVE BEEN 363.8). THERE WAS A LOT OF CHATTER ON THE RADIOS AND I BELIEVE ICS MAY HAVE BLOCKED PART OF THE CTLR'S REQUEST FOR A SPD REDUCTION. I HAD BEEN DOING ABOUT 330 KIAS IN THE DES; BUT SLOWED TO 250 KIAS AT 10000'; SO I ASSUMED THAT WAS WHAT HE WANTED; ALTHOUGH I WASN'T TOO SURE IF HE WAS TALKING TO ME BECAUSE THERE WAS A TAC CALL SIGN 2 ACFT BEHIND ME AND THE CALLSIGNS WERE BEING CUT OUT A BIT BY THE INITIAL MIC CLICK. ALSO; THE CTLR'S RADIO WAS COMING IN A BIT BROKEN; WHICH WAS CONFIRMED BECAUSE HE HAD TO ASK THE TAC CALL SIGN 2 ACFT SOMETHING TWICE BECAUSE OF THE POOR XMISSION QUALITY. WHEN I CHKED IN ON FREQ AT 9000' THE CTLR SAID I WAS SUPPOSED TO BE AT 10000'. BECAUSE HE WAS STILL COMING IN BROKEN I TOLD HIM THAT AND ASKED WHAT ALT DID HE WANT ME AT; '9000 OR 10000'?' HE SAID TO MAINTAIN 9000'. DURING THIS EVOLUTION I SPOTTED WHAT APPEARED TO BE AN AIR CARRIER AT MY 1 O'CLOCK; NOSE ON; AND MAYBE 4 OR 5 MI AWAY AT ABOUT THE SAME ALT; WITH WHAT APPEARED TO BE HIS LNDG LIGHT ON. THERE WASN'T A TFC CALL; BUT I THOUGHT LATER THAT PERHAPS THE CTLR WAS TRYING TO USE ALT TO SEPARATE US. A TURN TO HDG 250 WAS GIVEN TO ME AND COMPLIED WITH; ALTHOUGH THE TFC DIDN'T APPEAR TO BE A FACTOR TO ME. THE CTLR DID THANK SOMEONE ON VHF THOUGH; SO I WASN'T TOO SURE OF WHAT THEIR PERCEPTION WAS AT THE TIME. THE CTLR SOUNDED EXTREMELY BUSY; AND A QUICK CALL TO DES TO 7000'; THEN 4000' AND A TURN TO 330 DEGS FOLLOWED. HE CALLED ME TAC CALL SIGN 2 ALSO; ADDING TO THE CONFUSION; AND I THINK I HEARD THE OTHER ACFT RESPOND WITH SOMETHING. HE THEN ASKED ME TWICE TO CONFIRM THAT I WAS TAC CALL SIGN 1 ON 337.2; WHICH I DID BOTH TIMES. I WAS HANDED OFF TO A FINAL CTLR; WHO INITIALLY ALSO CALLED ME TAC CALL SIGN 2. AN UNEVENTFUL PAR FOLLOWED; ALTHOUGH THERE WERE 2 TFC CALLS NEAR THE COASTLINE AT 1 O'CLOCK; AND I SPOTTED ANOTHER ACFT AT ABOUT OUR 10 O'CLOCK. I MENTIONED TO THE RADAR OFFICER ON ICS THAT IT WAS LIKE THREADING THE NEEDLE OUT HERE TONIGHT. BECAUSE OF THE REQUEST TO CONFIRM MY CALL SIGN AND FREQ; THE CTLR'S OBVIOUSLY IRRITATED TONE OF VOICE; AND THE APPARENT CONFUSION ABOUT MY ASSIGNED ALT; I BEGAN TO SUSPECT HE MIGHT CONSIDER FLT VIOLATING ME; HENCE; I DECIDED TO MAKE THIS STATEMENT. THE RADAR OFFICER WAS NOT CERTAIN ABOUT THE 9000' DES REQUEST BECAUSE HE HAD MENTALLY TUNED OUT ALL THE FAST AND FURIOUS CHATTER; SO HE ALSO SUGGESTED THAT I MAKE THIS STATEMENT.