The two American military attachés who were expelled from Russia early this month, days ahead of the Victory Day martial parade on Red Square, had made an uninvited visit to a military aviation factory in Siberia that Russia regards as strategic, several American officials said.

The unannounced visit occurred in late March at the Novosibirsk Aviation Production Association in the Name of V.P. Chkalov, a plant that manufactures Sukhoi-34 fighter-bombers, known as Fullbacks by NATO designation. The two officers involved, a U.S. Army lieutenant colonel and U.S. Navy lieutenant commander, appeared at the factory's gates and were subsequently questioned by the surprised local authorities, three American officials said.

The Russian government later asked for them to leave the country, a request the United States honored.

Both the United States and Russia have provided very little information about the reasons behind the expulsions. But the more detailed account of the officers' travels and the Russian reaction appeared to undercut in part the assertion last week by Defense Secretary Robert Gates that the attachés had fallen victim to simple tit-for-tat retaliation for two Russian diplomats expelled from the United States.