Air carrier flight crew cleared for a visual approach mistakes OPF for FLL. The crew begins to question at the same ATC confirms they are lined up for the wrong airport.

Narrative

This incident happened on the first day of a 2-day trip. Neither the First Officer nor I had flown to any of the airports in Florida that were included in this trip. Before the first leg of the day; the First Officer and I thoroughly reviewed the airports; airways; and local procedures for the first day's legs. The First Officer flew the first leg which was uneventful; and I flew the second leg to FLL. Our departure and enroute phases were also uneventful. The Center Controller vectored us to the south once we started our descent into the FLL/MIA area so that we would be flying northbound toward the FLL airport on our approach. After being handed off to the MIA Approach Control; we were instructed to descend to 2;000 FT MSL and given a heading of about 060 degrees to fly. The Approach Controller instructed us to expect a visual approach for Runway 9R. The weather was just slightly hazy and becoming dusk. We visually scanned the area for the airport for well over 10 miles. The Controller continued to give us instructions that the airport was 12 o'clock position and about 11 miles. FLL International Airport's layout consists of 3 runways: Runway 9L/27L; 9L/27R; and 13/31 with lengths of 5;276 FT; 9;000 FT; and 6;930 FT respectively. Runway 9R has a LOC approach which we had briefed and the frequency was set into the navigation radio. We spotted what we believed to be the FLL Airport roughly our 1 o'clock position and about 6 or 7 miles. I visually verified it to be the FLL Airport by comparing it to the airport diagram; which had 2 east/west runways and what looked to be northwest by southeast crossing runways. We told MIA Approach that we had the airport in sight and we were cleared to fly the visual approach to Runway 9R. I entered the pattern on a 45 degree base leg to final; and started a descent. At about 4-5 miles out and at approximately 1;400 FT MSL; both the First Officer and I started to question if this was in fact the correct airport. I believe the airport that we actually saw was OPF which is 12 miles south-southwest of FLL or HWO which is 6 miles southeast of FLL. OPF has 3 runways: Runway 9R/27L; 9L/27R; and 12/30 and lengths of 4;306 FT; 8;002 FT; and 6;800 FT respectively; and HWO has 2 North/South and 2 East/West runways. These runways also include Runway 9R/27L and 9L/27R which are 3;200 FT long each. The fact that OPF and HWO have the same runways as FLL; coupled with fact that my LOC needle was showing only 1 dot off course when I started my descent lead me to believe it was in fact FLL. Once we were closer and on final; I determined that the buildings did not look like the large terminal complex depicted on the airport diagram and questioned the First Officer. I started to level off from the descent and was about to call approach to verify that they showed us on final for Runway 9R. Before we got a call off; the same Approach Controller called us and said we appeared to be lining up for a different airport that was 11 miles south of FLL. We were given a climb back to 2;000 FT MSL and told that FLL Airport was still at our 11:30 o'clock position and still 11 miles. After asking for and receiving a heading to fly; we visually acquired and landed at FLL Runway 9R. I believe this event occurred for several reasons: 1) Both pilots were unfamiliar with FLL; and the surrounding area. 2) The environmental conditions played a small but significant role in this incident. Although the low light and slight haze did not constitute a significant weather phenomenon; these 2 factors combined with the low altitude had a significant effect on our depth perception and ability to discern fine detail from a low distant angle. 3) The distances and directional information that ATC was providing was possibly flawed and vague. The final distance that we were instructed to look for the airport was considerably less distance than we actually flew; and the directional information had us looking at several airports that looked very similar to FLL. 4) I believed the indication that I was receiving on my course display was accurate. My CDI indicated about a 1 dot deviation off course when we visually acquired the wrong airport. I believe that in fact it did not have a valid signal because we were well over 60 degrees off of centerline for the antenna for Runway 9R at FLL. I also failed to verify the DME reading was consistent with our position. 5) I neglected to ensure that the Runway 9R approach was programmed into the FMS and displayed on the MFD. This oversight would have significantly increased our situational awareness. There are 2 reasons for this oversight. First; I was using the TCAS portion of the display and did not consider switching back and forth from TCAS and navigation modes. Second; I typically set up all approaches in the FMS when I am the pilot not flying; especially when operating at unfamiliar airports. As the pilot flying; I did not ask the First Officer to do the same for me. I should have ensured that this was done in this instance.