TCASII. RPTR ACFT CLRED TO DSND THROUGH ANOTHER ACFT ALT. TCASII ALERTED FLC WHO ACQUIRED INTRUDER TFC VISUALLY. FREQ CONGESTION AND BUSY APCH CTLR CONTRIBUTED TO OCCURRENCE.

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ON ARR INTO LGA WE WERE TURNED TO ABOUT A 040 DEG HDG AND TOLD TO DSND TO 7000 FT. THE WX WAS VFR AND WE WERE 20 MI OUT AND ABLE TO SEE THE ARPT ALREADY. WHILE DSNDING THROUGH 7400 FT WE RECEIVED A TA FROM OUR TCASII. AT ABOUT 7100 FT WE GOT AN RA TELLING US TO 'INCREASE DSCNT.' WE HAD A VISUAL CONTACT WITH THE TFC (COMMUTER) BUT IT LOOKED SO CLOSE THAT WE OPTED TO CONTINUE DSCNT AS PER TCASII INSTRUCTION. AS THE COMMUTER PASSED OVERHEAD I BELIEVE I SAW HIS ALT AS 7400 FT ON OUR TCASII. I BELIEVE THE PROB WAS CAUSED BY LGA APCH BEING REAL BUSY AND MAYBE THEY WEREN'T IN RADIO CONTACT WITH THE COMMUTER. AT ANY RATE; THEY APOLOGIZED AND ALLOWED US TO STAY AT 6700 FT AND WHEN TFC WAS NO LONGER A FACTOR; CLRED US TO 4000 FT. THE REST OF THE APCH AND LNDG WAS UNEVENTFUL. WE WERE ALSO DEALING WITH A SICK PAX THAT MAY HAVE TAKEN AWAY SOME OF OUR ATTN; WHICH MIGHT HAVE ALLOWED US TO HAVE GOTTEN AN EARLIER VISUAL CONTACT. THIS INCIDENT HAS MADE ME VERY CONFIDENT OF TCASII CAPABILITIES. EVEN THOUGH WE HAD VISUAL CONTACT; SOMETIMES IT IS SO CLOSE THAT THE BEST COURSE OF ACTION IS TO FOLLOW THE TCASII. IT WORKS!