Rep. Thomas P. O'Neill Jr. (D-Mass), majority leader of the House of Representatives, said yesterday that President Nixon may resign in April or May to prevent a public disclosure of the evidence now held by Judge John Sirica.

The Cambridge Democrat said that Sirica is expected soon to turn over the evidence to the House Judiciary Committee. "Rather than see the evidence made public, I think the president will resign," he said.

"From what I've seen the evidence is very damaging," O'Neill said. He said that special Watergate prosecutor Leon Jaworski could have indicted the president.

"I'd hate to see the President of the United States indicted," O'Neill said.

O'Neill said Vice President Gerald R. Ford would "give stability to the country and re-establish credibility in government" if he becomes president.

O'Neill made his remarks in an off-the-record seminar before a group of 50 students at Winthrop House. WHRB later relayed his statements to the Associated Press.

WHRB officials said last night they did not believe the remarks to be off the record, but barred only from direct broadcast.

In parts of the address that O'Neill later put on the record, O'Neill said that the Nixon administration has been "corrupt and venal," and he called for Nixon's resignation in the "best interests of the country."

He said also that if Nixon does not resign he is entitled to every constitutional protection during the impeachment process.

O'Neill said that if the impeachment question reaches the floor of the House for a vote, he compares his duty to that of a grand juror deciding whether to grant an indictment. He said he will let the Judiciary Committee make its presentation of the facts before he decides how he will vote.

He said the Democratic Party does not hope to gain power through impeachment, but that it wants to perform the constitutional responsibility of the Congress.