NMAC -- ACR HAS AN NMAC WHEN A LIGHT ACFT OVERSHOOTS ITS FINAL APCH TO A PARALLEL RWY AND FLIES UNDER THE ACR.

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ON JUL/SUN/95 I WAS FLYING A JETSTREAM ON APCH TO (MRY) MONTEREY; CA. IT WAS VMC WITH HAZE. WE WERE ON A L DOWNWIND FOR RWY 28L WHEN A C-152 (FEMALE; WITH HVY FRENCH ACCENT) ALSO RPTED L DOWNWIND. I IMMEDIATELY BECAME CONCERNED UNTIL THE TWR CAME RIGHT BACK AND CORRECTED HER BY SAYING SHE WAS ON A R DOWNWIND AND WAS CLRED TO LAND ON RWY 28R. SHE RESPONDED CLRED TO LAND RWY 28R. I WAS STILL CONCERNED ABOUT THE C-152 PLT'S AIRMANSHIP SO I TOLD MY FO I WAS GOING TO MAKE A HIGH/SHORT APCH TO RWY 28L TO REMAIN WELL CLR OF THE CESSNA. WE TURNED BASE AND THE CESSNA RPTED BASE WITHIN 10 SECONDS. WITH THE CESSNA PLT'S APPARENT INEXPERIENCE I WOULDN'T HAVE EXPECTED HER TO TURN BASE SO SOON; BUT SURE ENOUGH I SPOTTED HER COMING DIRECTLY AT US MAYBE 100 FT BELOW US. FROM WHERE I SAW HER I KNEW SHE WOULD OVERSHOOT BOTH HER FINAL (RWY 28R) AND RWY 28L'S FINAL BY A BIG MARGIN. MY FO CONFIRMED THAT SHE OVERSHOT BOTH RWYS AND COMMENTED IT WAS A GOOD CALL TO STAY HIGH AND SHOOT A SHORT APCH OTHERWISE SHE MAY HAVE HIT US. DOING SIMULTANEOUS VISUALS WITH CLOSE PROX PARALLEL RWYS WITH VARIOUS LEVELS OF EXPERIENCE IS COMMON AT MRY; FAT; AND VERY OFTEN AT SNA. IN THE FUTURE I WILL NOT TURN BASE UNTIL I SEE THE PARALLEL TFC AND KNOW WHEN I'M ON FINAL THERE WILL BE PLENTY OF SEPARATION IN CASE OF AN OVERSHOOT. I WOULD RECOMMEND THAT TWRS DEMAND ACFT HAVE SOME KIND OF SEPARATION ON FINAL TO PREVENT THIS SIT. THAT IS TWRS WHO HAVE VERY LOW TIME PLTS OPERATING.