The Sunday Times announced today that it would not proceed with plans to publish the purported Hitler diaries but would continue with its own investigation into the authenticity of the material.

Historian Hugh Trevor-Roper, whose initial conclusion that the diaries were genuine led the newspaper to buy British and Commonwealth rights to them, said today he had been "convinced for some time they were forgeries." About his earlier declarations, Trevor-Roper told reporters, "I should have refused to give an opinion so soon. . . . I should have said I need more time to reflect on them." Trevor-Roper declined to blame anyone else for the blunder. "It is my fault," he said.

In a statement, The Sunday Times tied its decision to acquire the diaries for $400,000 directly to Trevor-Roper's assurances as well as to those of West Germany's Stern magazine, which first turned up the material. Trevor-Roper, who also is Lord Dacre, is a director of Times Newspapers Ltd., parent company of The Sunday Times.

The statement said that The Sunday Times "accepts the report of the German government archivists" that the material they examined is not authentic. But, it said, an independent investigation of two volumes of material brought to London this week is under way and "the experts' opinions will be published." Meanwhile, no extracts will appear, the statement said.

Arthur Brittenden, a spokesman for The Sunday Times, said half the money to Stern already had been paid. "There will be no further payments," he said, but insisted he was unaware of any provisions for Stern now to refund any of the money.

The Sunday Times has reversed itself several times in the course of the controversy over the diaries. When Trevor-Roper's flat assertion that the material was authentic appeared last month in the daily Times, The Sunday Times next day published copious details of how the material had been found and what it contained.

But when Trevor-Roper expressed doubts at a press conference called by Stern in Hamburg, the newspaper strongly implied in an announcement that it would not go ahead with publication until it was satisfied that the diaries were genuine. Then the newspaper said this week that diary material would appear after all, apparently because of a continuing belief among members of the staff that despite the widespread skepticism, the diaries are legitimate.

Sunday Times reporters have fanned out in Germany, "tracking over the same ground as Stern," as one put it, to establish how the material was handled since it allegedly disappeared at the end of World War II. The Sunday Times Magazine, which is printed in advance, will contain material in this Sunday's issue chronicling Hitler's career, but it does not have extracts of the purported diary.