The Soviet government announced tonight that it has ordered the expulsion of a U.S. diplomat after he allegedly was caught "in the act of conducting an espionage action" yesterday.

An official statement issued by the Tass news agency said Paul Stombauch, a second secretary in the political section of the U.S. Embassy in Moscow, was seized in Moscow yesterday by agents of the Soviet secret police, the KGB, who "cut short a major espionage action by United States special services against the Soviet Union."

The wording of the Tass statement appeared to suggest that several Soviet citizens may have been seized for their links to Stombauch.

Spokesmen for the U.S. Embassy refused all comment beyond confirming that Stombauch worked in the political section, that he has a wife and son with him here, and that they have been in Moscow since last summer.

There was speculation in western circles here that the prompt announcement of Stombauch's expulsion may be linked to the potential embarrassment caused by the FBI probe of the Walker spy ring in the United States.

By announcing that a "major espionage action" by the CIA was discovered in Moscow, the Soviets presumably sought to make it clear that both superpowers are engaged in spying on each other.

The announcement two years ago of the expulsion of Richard Osborne was made in similar circumstances. It came after a number of western countries expelled a large number of Soviet diplomats on espionage charges.

During the investigation of Stombauch, Tass said, "materials were obtained by the KGB fully exposing this staff member of the U.S. Embassy as engaging in espionage activity incompatible with his official status."

"For his unlawful action," Tass said, Stombauch "was declared persona non grata and is being expelled from the Soviet Union."

Osborne, a first secretary of the embassy, allegedly was caught "red-handed" with incriminating espionage gear, including a radio transmitter, in March of 1983.

A year later, two junior members of the embassy staff were detained by Soviet security agents while meeting a Soviet dissident on a playground. They were accused publicly of espionage but were not ordered expelled from the Soviet Union.

In the past, U.S. diplomats accused of spying were ordered quietly out of the country. Moscow usually treated such expulsions discreetly and publicized them a long time after they took place.

Prior to Osborne's expulsion, the last previous expulsion on espionage charges involved Martha Peterson, a member of the embassy consular section, who allegedly was caught "red-handed" in the summer of 1977. The Soviets disclosed the news of her expulsion a year later.