As many as 30 political prisoners are being held in psychiatric hospitals despite claims by President Mikhail S. Gorbachev that the Soviet Union no longer has political detainees, activists say.

The Soviet leader told the United Nations last month that "no persons convicted for their political or religious beliefs" are being held in his country.But the activists told a news conference in a cramped apartment the names of three people they say are political prisoners in psychiatric hospitals. Two other men at Wednesday's news conference said they were former political prisoners and have been released in the past six months.

The U.S. State Department has credited the Soviets with "significant progress" in its treatment of political prisoners, saying it has freed all those held under laws limiting expressions of political and religious beliefs. But a U.S. official has said it still has questions about 30 prisoners who are considered criminal violators by the Soviets.

A delegation of American psychiatrists is expected to arrive in Moscow in late February to visit alleged political prisoners being held in psychiatric hospitals, according to U.S. Embassy spokesman Mike Hurley. He said the group expects to see about 20 patients.

Alexander Novikov, 27, who said he was hospitalized as a schizophrenic after distributing "leaflets on democratic rights," said he personally met seven other political prisoners at the Chernitovskaya Hospital near Leningrad, where he was held until October. He said none seemed mentally disturbed to him.

Through them, he said he learned of 20 political prisoners at that institution alone.

"The doctors are sadists," said Novikov, whose complexion was still white from his years of confinement. "These hospitals don't have a medical function, they have a criminal, punishment function."

"And this is in the time of glasnost, perestroika and democratization, in the time of Gorbachev," said activist Alexander Podrabinik.