The Soviet news agency Tass said today that a Soviet citizen was sentenced "to a long term in prison" for spying for the U.S. Central Intelligence Agency.

The sentence was imposed by the Soviet Supreme Court, Tass said. It identified the man as A. Ivanov and said, "An investigation has brought to light facts incontrovertibly testifying to the involvement of a number of staff members of the U.S. Embassy in Moscow."

A spokesman for the U.S. Embassy declined to comment on the Tass report.

The fact that Ivanov was given a long prison term rather than death, the maximum penalty for espionage, appeared to indicate that he had cooperated fully with the authorities following his arrest.

Tass said that at the time of Ivanov's arrest Soviet security agents seized CIA instructions for collecting information and for "the maintenance of secret communications." It said other materials for espionage activities were found in his possession.

The brief report provided no other details and gave no indication of when Ivanov was arrested and tried.

An American diplomat was ordered expelled from Moscow in March after Soviet authorities announced that he had been caught "red-handed" with incriminating espionage equipment. According to Tass, he was seized while working with "portable intelligence special purpose" equipment used for the transmission of information via a U.S. communications satellite.

The Tass announcement in March suggested that the U.S. diplomat may have been showing someone how the equipment was being used.

Another American diplomat in Moscow was ordered to leave the country in June when the Soviet secret police, the KGB, announced that he also was caught "red-handed during a spy action in Moscow on June 2."

The announcement of that expulsion gave no details about the alleged "espionage activities" of the American.

It was not possible to determine whether either of the two expulsions was linked to the Ivanov case.

The last Soviet citizen to be arrrested as an American agent was Yevgeny Kapustin. His arrest was reported in September 1981, but no account of his trial ever was made public.

Other than the expulsions of the two Americans this year, the last known case of a U.S. Embassy employe being expelled from Moscow on espionage charges was in the summer of 1977. Subsequently, an embassy first secretary was ousted from Moscow in January 1978 in retaliation for the expulsion from Washington of a Soviet trade official.