B737 FLC HAS FUEL IMBAL PROB; RETURNS TO DEP ARPT; MIA.

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AFTER BRAKE RELEASE; NOTICED R CTR FUEL LOW PRESSURE LIGHT ILLUMINATED. CHKED MEL AND IT APPEARED WE WERE OK TO CONTINUE. BRIEFED FO WHEN ENRTE TO SEND MESSAGE TO DISPATCH TO NOTIFY MAINT AND IF THE L SIDE LIGHT LOW PRESSURE LIGHT ILLUMINATED ONLY WING TANK FUEL WOULD BE USABLE AND WE WOULD RETURN TO MIA. WHEN RUNNING ABNORMAL CHKLIST; I CONFUSED 'MAIN TANK' PORTION OF THE PROC WITH THAT OF 'CTR TANK' AND DIDN'T READ ANY FURTHER THINKING IT DIDN'T SAY 'WING TANK(S)' AND TURNED OFF THE 'AFFECTED SIDE' (R SWITCH). ON CLBOUT AT APPROX 16000 FT; THE 'FUEL IMBAL' ILLUMINATED AND I NOTICED THE R WING TANK FUEL QUANTITY DECREASING RAPIDLY. I IMMEDIATELY SUSPECTED A FUEL LEAK WHICH DICTATED THE FURTHER COURSE OF EVENTS/ACTIONS. EMER DECLARED AND RETURNED TO MIA. SINCE I SUSPECTED A FUEL LEAK I DID NOT ATTEMPT TO BAL FUEL THINKING IT MIGHT RESULT IN PUMPING NEEDED FUEL OUT OF AN OPEN HOLE SOMEWHERE. CLOSER TO MIA WE ATTEMPTED TO BAL FUEL TO ADDRESS HVY WING PROBS BUT ONLY WHEN LNDG WAS ASSURED. I MADE LOGBOOK ENTRIES FOR R CTR BOOST PUMP; SUSPECTED FUEL LEAK; OVERWT LNDG; AND TAXI WITH FUEL IMBAL. AT GATE THE R CTR FUEL PUMP OPERATED NORMALLY.