ACR LGT IAP ILS APCH TO THE WRONG RWY FOLLOWED BY GAR AND SECOND APCH TO THE CORRECT RWY.

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WHILE SHOOTING AN APCH TO ULS 12R AT STL COPLT HEARD CTLR SAY 'EXPECT 12L.' THE CAPT DID NOT HEAR THIS OR CONFIRM THIS AS COPLT HAD ASKED. AFTER MUCH DISCUSSION THE CREW DETERMINED THAT STL WAS SHOOTING APCHS TO 12R. THERE WAS A LOT OF SWITCHING OF NAV RADIOS BECAUSE OF THE CONFUSION OVER THE RWY. THE CAPT WAS ON LOC/DME FOR DISTANCE INFO FROM THE FIELD. I INTERCEPTED WHAT I BELIEVED TO BE THE 12R LOC AND WAS CLRED FOR THE APCH. I NOTICED A SLIGHT CORRECTION TO THE R TO MAINTAIN COURSE. THE CAPT NOW WANTED TO USE MY RADIO FOR HIS #1 RADIO AND WE HOOKED UP THE AUTOPLT TO SHOOT A COUPLED APCH. THE ONLY PROBLEM IS 108.9 IS THE LOC TO 12L AND WE WERE CLRED FOR 12R. I NOTICED THE NEEDLE ABOUT 1/2 DOT TO THE L AND THE CAPT MENTIONED TO BE AWARE THAT WE ARE CORRECTING L AND WE SHOULD HAVE A XWIND FROM THE R. HE WAS STILL ON THE VOR GETTING A XING FIX ON THE COPLTS #2 RADIO. WHEN HE FINALLY PUT THE #2 ON THE ILS FREQ HE MATCHED THE ONE IN #1 NAV WHICH WAS WRONG. WE BROKE OUT AT 500 FT SAW THAT WE WERE LINED UP FOR 12L AND TOLD TWR THAT WE WERE EXECUTING A MISSED APCH. WE CAME AROUND AND SHOT THE APCH AND LANDED. THE PROBLEM AROSE WHEN THE 1 CTLR SAID EXPECT 12L. I ASKED THE CAPT TO CONFIRM THAT AND I THOUGHT HE WAS IGNORING THAT AS A BAD IDEA WHEN IN RETROSPECT I BELIEVE HE DIDN'T HEAR ME. ALSO THE CAPT'S NEED TO GET SUPERFLUOUS INFO SUCH AS DISTANCE FROM THE FIELD AND XING INFO CREATED UNNEEDED CONFUSION. I BELIEVE SOME OF THE CREW WAS FATIGUED FROM WORKING OTHER JOBS BECAUSE OF THE UNCERTAINTY OF THE AIRLINES FUTURE.