WDB ON ARR FROM OCEANIC FLT HAS TCASII RA TO DSND. DOES SO. CONTINUING ON APCH HAS SECOND TCASII ALERT TO PULLUP.

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APCHING ON BT6 025 DEG RADIAL 29 DME FIX; FO WAS FLYING LEVEL AT 10000 FT; SLOWING TO 210 KTS AT PDX TRACON'S REQUEST. I NOTICED TFC APCHING ON TCASII DISPLAY BUT WAS NOT TOO CONCERNED. THE TFC WAS NEVER MENTIONED BY ATC; IN SPITE OF THE FACT THAT WE WERE CLOSING WITH IT. THE TCASII SOUNDED 'TFC; TFC' BUT NEITHER ONE OF US COULD SEE IT. AT ABOUT THE TIME I SAW THE MERGING TFC; THE DISPLAY TURNED RED AND ANNUNCIATED 'DSND; DSND.' FO IMMEDIATELY CLOSED THE THROTTLES AND BEGAN A DSCNT. THE HIGH WING; LIGHT ACFT FLEW OVER US BY ABOUT 400 FT. THERE WERE ALSO A LINE CHK AIRMAN AND AN FAA ACDP INSPECTOR ON BOARD; BOTH OF THEM OBSERVED THE ENTIRE SCENARIO. FO RESPONSE WAS BOTH TIMELY AND APPROPRIATE. ONLY MINS LATER; WHILE ON FINAL APCH TO RWY 10R AT PDX; A SECOND TCASII ALERT CHANGED TO WARNING RESULTING IN A PULLUP; WHILE WE WERE DSNDING FROM THE FINAL APCH FIX INBOUND. THIS WAS CAUSED BY AN ACFT AT A SMALL ARPT TO THE IMMEDIATE NW FLYING A TFC PATTERN OVER THE RIVER. THE HORIZ FLT PATTERNS OVERLAPPED. WE WERE TOO CLOSE TO THE OTHER ACFT; AND THE VERT AVOIDANCE MANEUVER --- PARTICULARLY WHEN ONE HAS BEEN FLYING ALL NIGHT FROM THE ORIENT -- RESULTED IN SOMETHING LESS THAN WHAT IS CONSIDERED A STABLE APCH.