The Stuttgart dealer in Nazi artifacts who sold the bogus Hitler diaries to the West German magazine Stern surrendered to police today at a Bavarian border post.

In a statement issued by his lawyer, Konrad Kujau admitted that he supplied most of the 62 volumes of diaries to Stern reporter Gerd Heidemann but said he was convinced at the time that they were genuine.

Kujau, who also used the name Fischer, said he was turning himself in "voluntarily, to defend myself against the accusations of fraud made against me."

Kujau denounced reports that he had forged the diaries as "absurd" and said he acquired them from two suppliers in East Germany.

He also disputed Stern's claim to have paid $3.75 million for the diaries, saying he received only slightly more than $1 million from Heidemann in installments and passed along all but $125,000 to his East German suppliers.

Stern journalists staged a sit-in yesterday at the magazine's office to protest the hiring of two new editors, known for their conservative views, to replace editors who resigned in the wake of the Hitler diary hoax.

Editorial staff members, who were angered by management's secrecy in handling the diaries and its refusal to seek outside verification, adopted a resolution saying that the two appointments threatened the editorial independence of the left-liberal newsweekly.

In his statement, Kujau said he left East Germany in 1957 to settle in the West and built up a collection of Third Reich memorabilia while managing a succession of businesses with a woman friend.

He said he returned to East Germany for the first time in 1969 and discovered a number of people interested in selling prewar memorabilia for western currency.

In 1978, Kujau said, he met a man named Mirdorf, who offered him a volume of Hitler's diaries. Kujau brought the book back to Stuttgart, where he said several collectors and historians examined the diary and pronounced it genuine.

In London, Hugh Trevor-Roper, the historian who at first said he believed the fake Hitler diaries were authentic, apologized to the public Saturday in an article in the Times of London, The Associated Press reported.

"I made a grave error in my first judgment," Trevor-Roper said. "But within the limits which I wrongly accepted, I do not think that judgment was irrational." Trevor-Roper examined some of the diaries in Zurich April 7, about a month before the West German government denounced them as fakes.

In late 1980, Kujau said, he was approached by Heidemann, who pressed him to acquire more diary volumes on his trips to the east.

Kujau said he rejected an initial offer of $62,500 from Heidemann but decided to cooperate when the reporter produced from his own collection a blue dress uniform worn by Nazi Luftwaffe chief Hermann Goering.

For more than two years, Kujau said, he acquired the diaries, usually two or three at a time, from Mirdorf and another East German named Lauser. Kujau said he picked up the first volumes in East Germany, but later transactions were conducted in Switzerland and West Germany.

He said Heidemann made several direct payments to his suppliers and strongly denied that the reporter gave him as much as $3.75 million.

Kujau insisted that he was told by Heidemann that experts had concluded that the diaries were authentic. The Stuttgart dealer ridiculed the notion that he had forged them himself, saying "I can neither read nor write old Germanic script."

Lawyer Rolf Schmidt Diemitz said his client had been escorted to Hamburg for questioning by the public prosecutor's office in connection with a fraud suit filed against Heidemann by Stern which fired the reporter May 10.

Several senior journalists at Stern have threatened to quit because of the way management has handled the diaries affair.

The sudden appointment of the two new editors-in-chief, Johannes Gross and Peter Scholl-Latour, provoked an office sit-in by a journalists' "editorial council," which insisted that the hiring of the two editors should be revoked.

Gross has been publisher of the business magazine Capital and hosts a popular political talk show on television. Scholl-Latour, a veteran foreign correspondent, is currently the Paris bureau chief for a West German television channel.