Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Conflict NMAC
Flight Crew Took Evasive Action; Flight Crew FLC complied w / Automation / Advisory
Procedure
We were inbound on the 28L Commuter Visual and PDX Approach pointed out an orbiting C172 on the final in the vicinity of LAKER NDB at 1;900 FT. We were on glide path about to configure for landing. Both ILS and FMS glide paths cross abeam LAKER around 2;000 FT; so we knew this encounter was a serious potential safety threat. The C172 was being flown under an 'XXXXX' call sign; which I believe to be some type of police drug eradication operation. I have encountered these XXXXX flights before; and they often loiter smack in the middle of runway approach paths at both PDX and SEA. Why ATC allows this is a mystery to me; because it's clearly dangerous. When we first sighted the bogie; it was at our 1 o'clock and appeared to be southbound. If the aircraft had continued in that direction; it would have cleared the final and been out of our way. Instead; the C172 turned directly into us as we descended on the published glide path. We immediately got a traffic alert and then a 'climb; climb' RA; which we expeditiously complied with. At our closest point we were 0 feet lateral and approximately 200 FT vertical. I don't believe ATC would allow any aircraft to orbit in these critical Class B and C airspaces. Except for these police flights; this is not the place to play airplane 'chicken.'
Air Carrier Captain reports a NMAC with a C172 orbiting near the FAF for Runway 28L at PDX. Captain questions the advisability of allowing this aircraft to operate at this location and altitude regardless of its mission.