C182 PILOT REPORTS CONFLICT WITH ANOTHER ACFT; UNDER TOWER CONTROL; DURING VISUAL APPROACH.

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IT WAS A CLR DAY WITH GREAT VISIBILITY. I WAS IN THE R SEAT OF A C182 WITH A TRAINEE IN THE L SEAT. WE WERE APCHING ZZZ FROM THE E AND WHEN WE CALLED WHILE ON R BASE WE WERE CLRED FOR THE OPTION ON RWY XX. WE HEARD RADIO TFC OF ANOTHER ACFT WITH THE TWR AND I RECALL THEY WERE TOLD TO BE #2 FOLLOWING OUR ACFT. THE C182 IS A HIGH WING PLANE AND I DID NOT SEE THE OTHER ACFT; BUT WAS BUSY WATCHING THE TRAINEE AND HIS PROCS WHILE PREPARING TO TURN FINAL. AS WE BEGAN THE TURN TO FINAL I SAW ANOTHER AIRPLANE WHICH WAS ON SHORT FINAL FOR A STRAIGHT-IN LNDG; THE OTHER AIRPLANE WAS BEGINNING TO MAKE A CLBING R TURN TO AVOID US. IT WAS ABOUT 500 FT (OR LESS) FROM US. AT THIS TIME I HEARD A VOICE OVER THE RADIO SAY 'HE TURNED RIGHT IN FRONT OF US.' I THEN CALLED TWR AND SAID 'TWR; THERE'S ANOTHER AIRPLANE HERE NEAR US; ARE YOU IN RADIO CONTACT WITH THEM?' THE TWR OPERATOR REPLIED; 'AFFIRMATIVE;' AND THEN SAID SOMETHING WHICH I INTERPED TO MEAN HE THOUGHT THE SITUATION WAS UNDER CTL. IF THE PLT OF THE OTHER AIRPLANE HAD NOT SEEN US AND EXECUTED AN EVASIVE MANEUVER THERE LIKELY WOULD HAVE BEEN A COLLISION. IN MY OPINION; THE TWR CTLR DID NOT HAVE CTL OF THE SIT AND WAS DIRECTLY RESPONSIBLE FOR ALLOWING AN UNSAFE SIT TO DEVELOP.