COMMUTER FLT HAS NMAC WITH SMA.

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NUMEROUS ACFT IN AREA. DURING DSCNT; TWR ADVISED US OF POTENTIAL TFC; RECOMMEND WE REMAIN AT OR ABOVE 7000 MSL. TWR AGAIN ADVISED OF TFC; 10-11 O'CLOCK POS AND APPROX 7000 MSL (NOT SURE ON THIS ALT). BOTH PLTS LOCATED TFC AT 10 O'CLOCK MANEUVERING (WE'RE AT 9000-9500 AT THIS POINT). PLT (CAPT) ASKED ME: 'DOES THAT LOOK LIKE 7000 FT?' I SAID IT DID. I HAD THOUGHT THE TFC WAS CLBING; SO SEEING IT MANEUVERING STRUCK ME AS ODD. JUST AFTER THE ABOVE SHORT DISCUSSION; I SPOTTED AN SMA; 11:30-12 O'CLOCK CLBING/SLIGHT L BANK TOWARDS US; DISTANCE LESS THAN 1/4 MI. IMMEDIATELY BEGIN RAPID DSCNT; HARD R TURN. BOTH ACFT AROUND 8500 MSL AT THIS POINT. CONTRIBUTING FACTORS: 1) TWR ATTEMPTS TO GIVE GOOD TA'S AND SEPARATE TFC; BUT IS USUALLY UNDER HIGH WORKLOAD. 2) I BELIEVE WE; AS A CREW; MISTOOK WHAT WAS PROBABLY 2 SEPARATE TA'S (2 TARGETS) AS ONE. SPOTTING 1 ACFT MAY HAVE GIVEN US A FALSE SENSE OF SECURITY (EXTREMELY SHORT LIVED). CORRECTIVE ACTIONS: 1) OBVIOUSLY; AS A CREW; WE MUST BE EVER VIGILANT. 2) THIS TYPE OF SITUATION IS VERY COMMON AT PRESCOTT. VERY HIGH DENSITY STUDENT TRAINING IS CONDUCTED DURING DAYLIGHT HRS. IT SEEMS A RADAR APCH SYS IS BADLY NEEDED. TWR CTLRS ARE BUSY ENOUGH THAT ADVISING ARRS/DEPS IS HARD TO DO. 3) ALONG WITH 2) ABOVE; A MORE STANDARDIZED SYS OF ARR AND DEP PROCS. MIL TRAINING RELIES ON THIS APCH AND I THINK IT WOULD SERVE PRESCOTT WELL; RATHER THAN THE CURRENT WILLY-NILLY ENVIRONMENT.