MLG ON DSCNT HAS NMAC WITH SECOND ACFT.

Narrative

WE WERE BEING VECTORED BY ABE APCH CTL FOR ILS TO RWY 06 AT ABE. APCH ASSIGNED 180 DEG HDG AND THEY STOPPED OUR DSCNT AT 5000 FT AS WE WERE AT ABOUT 5200 FT. THE REASON FOR STOPPING AT 5000 FT WAS A VFR ACFT AT 4500 FT. APCH WAS TALKING TO THE VFR ACFT. THE VFR CAME INTO VIEW ON OUR TCASII AT ABOUT 5 MI AND 11 O'CLOCK; AND APCH ALSO POINTED OUT THE VFR. THE TCASII TARGET WAS MOVING DOWN AND TO THE L IN A MANNER THAT WOULD PASS OFF TO OUR L. WE CONTINUED 180 DEG AND 5000 FT AND VISUALLY SEARCHED FOR THE VFR. WE WERE UNABLE TO SEE THE VFR ACFT AT ANY TIME DURING THE INCIDENT. WHEN HE WAS ABOUT 2 MI AWAY THE VFR CHANGED COURSE TOWARD US; AND SHORTLY THEREAFTER THE TCASII INDICATED THE VFR WAS CLBING! TCASII INDICATED HE WAS BUT 300 FT LOWER THEN WE WHEN HE WAS AT ABOUT 1 MI AWAY. TCASII DISPLAYED AND SOUNDED A RA AND WE CLBED ABOUT 200 FT. THE TCASII TARGET PASSED VERY NEARLY THROUGH OUR SYMBOL. I TALKED WITH THE APCH SUPVR TO TELL HIM HOW IT APPEARED FROM OUR PERSPECTIVE. HE INDICATED THAT THEY SAW NOTHING UNUSUAL; AND THAT THE VFR NEVER ACKNOWLEDGED SEEING US. I JUDGE THAT THE VISIBILITY AT THAT POINT WAS MUCH LESS THEN REQUIRED FOR VFR. REGARDING THE TCASII: ON THE ONE HAND IT ENABLED US TO KNOW WHAT WAS HAPPENING; BUT ON THE OTHER HAND IN THE OLD DAYS I WOULD HAVE ASK FOR AN AVOIDANCE VECTOR. THAT MIGHT NOT HAVE HELPED SINCE THE VFR ALTERED COURSE TOWARD US AND CLBED. IT'S TOUGH TO MAKE THE SYS WORK WHEN PEOPLE FLY UNDER VFR RULES IN IFR CONDITIONS.