U.S. officials said Saturday following an unprecedented inspection of Soviet mental hospitals that they could not determine whether patients still are held because of their political beliefs.

A team of psychiatrists, lawyers and interpreters interviewed 27 patients and former mental patients in a review spurred by Western charges of widespread psychiatric abuses.The Soviet Union withdrew from the World Psychiatry Association in 1983 under pressure from the West. It has pledged to end abuses and hopes to be readmitted this year to the association.

At a news conference Saturday, the Americans refused to discuss individual cases or their conclusions about the Soviet mental health system.

"We will not deny that this has been a very sensitive and difficult undertaking to carry out to our full satisfaction," said delegation leader Robert W. Farrand of the State Department's Bureau of Human Rights and Humanitarian Affairs.

Asked if he could say if there were any political prisoners still in Soviet mental hospitals, Farrand responded that "no one can prove the negative."

He said, however, that the human rights situation in the Soviet Union had improved substantially. The number of people the U.S. government lists as political prisoners is "well down" from 750 two years ago, Farrand said.

"We would not have agreed as a government to come to Moscow in 1991 for a human rights conference if we had not been convinced that the question of political prisoners had, in the main, been resolved," he said.

The team's lead psychiatrist, Dr. Loren H. Roth of the University of Pittsburgh's Law and Psychiatry Program, said Soviet officials were late in providing some medical records and that some patients had been discouraged from consenting to interviews.

However, he said the group eventually was able to interview those people.

Delegation sources who spoke on condition of anonymity said they had no indication of retribution against patients who gave interviews.

Yuri A. Reshetov, head of the Soviet Foreign Ministry's Office of International Cooperation and Humanitarian Affairs, said there are no political prisoners in mental hospitals.

But he said some people named on Western human rights lists may be "undergoing treatment due to specific concrete actions against the law."

Of the 27 people interviewed, 15 were in mental hospitals and 12 were former mental patients, Farrand said.

The Americans visited seven mental hospitals, including facilities in Kazan, Leningrad and Chernyakhovsk under the control of the Interior Ministry, which is responsible for the Soviet Union's uniformed police.