Govts admit knowledge of crafts

I am wondering if anyone has these documents or have seen them. A friend of mine told me that in one of his college classes he remembers reading something about the only time the govt has acknowledged UFOs was in a document / talks between US and USSR on what to do about large UFOs being mistaken for a hostile nuclear attack and what to do about it.

Anyone know anything on this or have more real facts on these talks between these two countries???

[Edited on 4-6-2003 by bigbrother]