The Soviet Union lodged a "resolute protest" over the expulsion of a military attache allegedly involved in a spy operation aimed at learning how the U.S. government protects computer secrets.

Lt. Col. Yuriy Nikolayevich Pakhtusov, 35, was told to leave Thursday. An FBI investigation had led to his arrest Wednesday night, just a day after the Bush administration opened a high-level dialogue with the Soviet Union.Pakhtusov was described by a U.S. source as a significant catch because he is a member of the Red Army's GRU intelligence arm. One official said Pakhtusov was caught "red-handed."

But the Soviet Embassy issued a statement saying the expulsion order "could be only qualified as a deliberate provocation against a Soviet diplomatic official."

It denied that Pakhtusov engaged in any wrongdoing and said the embassy has lodged a "resolute protest" with the State Department.

State Department press officer Dennis Harter said the Soviet Embassy was informed that Pakhtusov was being expelled for "activities incompatible with his diplomatic status."

According to one government source, Pakhtusov was asked to leave by Saturday.

Soviet Foreign Ministry spokesman Gennady I. Gerasimov called the expulsion a "gross provocation" at a regularly scheduled news briefing Friday in Moscow, but he did not announce any retaliatory Soviet action.

He said "the U.S. side is assuming all the responsibilities" of the decision to expel Pakhtusov.