It sounds like you're describing KAL007: http://en.wikipedia.org/wiki/Korean_Air_Lines_Flight_007

There's a larger list of airliner shootdowns here, and this is the only incident which seems to match your recollection: http://en.wikipedia.org/wiki/List_of_airliner_shootdown_inci...

There's nothing in the wikipedia article about the USA's ability to track planes. We did have a radar station in AK, which may be what you're thinking of? According to wikipedia it didn't produce useful information, and wasn't necessarily tracking the plane at all points anyway: http://en.wikipedia.org/wiki/Korean_Air_Lines_Flight_007#U.S...

I don't think we've ever had the ability to track all planes in the world.