Education Secretary William J. Bennett said yesterday that prisoners infected with the AIDS virus should be isolated and authorities should consider not releasing those who threaten to infect others after they complete their sen- tences.

"It's a very tough issue," Bennett said on the CBS News program "Face the Nation."

"I don't think there is an easy answer to it. When a person has served his time, a person should be free to go," he aid. But "supposing that person says . . . 'When I get out, I'm going to take my revenge on society.' I think this is a hard question for us, and you may want to hold onto him."

Bennett was a major advocate of President Reagan's recent controversial decision to test for exposure to the deadly virus among all federal prison inmates and immigrants seeking permanent residency in the United States.

But Bennett's chief of staff, William Kristol, said later that the remarks about AIDS were "not meant to be announcing new guidance for the administration."

Bennett was traveling yesterday and unavailable for comment after broadcast of the taped program.

"As far as the federal issue, it would be in the Justice Department's ballpark," Kristol said. "And whatever we're talking about, we would have to be talking about what's legally permissible."

Kristol added that in any case most prisoners are in state custody and would be unaffected by federal policy.

The administration's emphasis on testing was challenged by Sen. Lowell P. Weicker Jr. (R-Conn.), who appeared with Bennett.

"We are in a fight against a very complex disease, and the emphasis should be placed on research and on education," Weicker said.

Later in the broadcast, Sen. Jesse Helms (R-N.C.) called for a quarantine of persons who test positive for exposure to AIDS. "Somewhere along the line we are going to have to quarantine if we are really going to contain this disease," he said.