The police chief of Sao Paulo announced today that he was "90 percent certain" that a body buried in this suburb in 1979 was that of Dr. Josef Mengele, the Nazi war criminal who has been the target of an intensified international search.

As police and medical experts removed bones from the grave of the man, who had used the name Wolfgang Gerhard, international Nazi hunters dismissed the find as a ruse or hoax.

"This is not the first time that there have been reports that he's dead or that we have had false information," Simon Wiesenthal, head of a Nazi documentation center based in Vienna and Los Angeles, said in New York. "I don't see ingredients in this that I can believe."

Officials said it might take up to two weeks to determine whether the remains were those of Mengele, the Nazi doctor who conducted genetic experiments on thousands of children at the Auschwitz death camp in Poland.

Sao Paulo Police Chief Romeu Tuma said he had obtained authorization to exhume the grave after a tip from the West German federal prosecutor's office had led to important testimony by an Austrian couple who had sheltered "Gerhard" in their suburban home and said that they had learned of his true identity before his death in a swimming accident at an Atlantic beach.

As hundreds of reporters and cameramen watched today, experts broke open the rotten casket lid of "Gerhard's" grave to remove earth-stained bones that still showed fragments of clothing and head hair. The remains were taken away in an open box for examination.

A cemetery worker declared that the ill-kept grave had not been visited since the body's hurried burial Feb. 18, 1979, attended by two mourners with German accents. The mourners had prevented officials from opening the casket lid at the time of burial.

Police Chief Tuma said the Austrian couple, Wolfram and Liselotte Bossart, claimed they had sheltered Mengele from the early 1970s until Feb. 7, 1979, when he was drowned in an accident at Bertioga, a beach about 60 miles from Sao Paulo, that may have been provoked by a cerebral hemorrhage. Police records confirmed that there was a drowning at Bertioga at the time.

The Bossarts gave their testimony after the renewed international search for Mengele, spurred by several reported sightings and offers of rewards totaling $3.5 million, had brought West German authorities to the Bavarian town of Guenzburg, near Munich, where the Mengele family has a factory.

Frankfurt public prosecutor Heinz Haueisen said investigators obtained a court order to search for documents in Guenzburg. Haueisen said letters and other documents "pointed us in the direction of Sao Paulo and Mengele's death," The Associated Press reported.

U.S. documents published this year showed that Mengele had been arrested by American occupation authorities in Vienna in 1947 but had been released there.

According to Wiesenthal's documentation center, Mengele left Vienna for Buenos Aires in 1949 and lived in Buenos Aires under his own name until 1960.

After Israeli agents captured Adolf Eichmann in Argentina in 1960, Mengele is believed to have moved to Paraguay, where he assumed another identity.

The Bossarts told Brazilian and West German officials that Mengele had entered Brazil in 1969 and had spent three years in Sao Paulo State on the farm of Janus Stammer, also Austrian, working as a gardener and handyman.

They then invited him on humanitarian grounds to move to their house in the suburb of Campo Limpo, where he later revealed his identity after gaining their confidence.

They said they had kept quiet for fear of reprisals and because they, too, were illegal immigrants.

Police officials said the Bossarts claimed that before moving in with them he frequently had visited them to listen to German classical music records but had shown great distaste for conversations dealing with the war period.

The couple, which was present at the exhumation, refused to answer reporters' questions there, and Liselotte Bossart left early in an emotional state.

Later, however, the Bossarts told reporters that the man buried here had been introduced to them in 1970 by Gerhard, the man whose identity he later assumed.

Bossart said Gerhard told them the man, whom they at first knew as "Pedro," was a fugitive because of problems related to World War II but that it was another year or two later before he told them he was Mengele.

"By then he was part of the family," Bossart said.

The real Wolfgang Gerhard, a widowed Austrian engineer, returned to Europe around 1975 and died in an auto accident in Austria. Gerhard had served Germany in the war as a corporal, but police said the help he and the Bossarts gave the fugitive apparently was not based on ideological grounds.

The man buried here as Gerhard was interred next to the grave of the real Gerhard's mother.

The Bossarts said that after the burial, Mengele's son had come to Brazil to collect his personal effects.

Police chief Tuma said early today he was "90 percent certain" that the body was indeed Mengele's.

"Based on the declarations and documents presented it's 100 percent certain, but I'm waiting for identification by medical experts," he said. The couple's legal position might also cast doubt upon their testimony, officials said.

Tuma, who was responsible for the arrest of Italian Mafia boss Tommaso Buscetta last year, enjoys considerable prestige here.

He also recalled that in 1969 the Nazi Franz Wagner had been found in Brazil.

Reporters at the cemetery noticed another grave bearing a picture of a German soldier with a swastika, but Tuma said he did not believe this was a "Nazi cemetery."

The coroner from Sao Paulo's Medical Legal Institute, Jose Antonio de Mello, said that dental records dating from 1937 or later sent from Germany would be examined.

The remains would be remounted to form a skeleton and cross-checked with reports that Mengele had a deformed finger. The process is expected to take several days.

Experts from Israel, West Germany and the United States were reported to be arriving in Sao Paulo to assist in the investigation, but Tuma maintained that the conduct of the inquiry would be exclusively Brazil's.

Through the day, Tuma's repeated declarations to the press underwent some important changes, including a revision of his claim to be "90 percent certain" of Mengele's discovery.

The authorship of a diary or notebook revealed by the couple after repeated interrogation was also a source of confusion.

At first Tuma indicated it was Mengele's, then suggested that another unnamed German was the author.

The exhumation was witnessed by West German diplomats and three representatives of the Brazilian federal criminal office, who appeared to be granting a degree of credibility to the couple's assertions.

Kurt Volker, assistant German consul here, said, "Identification of the body will leave us with certainty whether we are really at the end of the story of this Nazi war criminal. Josef Mengele was a black mark on the history of humanity.

"I have full confidence in the high caliber of the Brazilians' work, but we are ready to help in this case," he said.

According to Tuma's assistant, Detective Aparecido Calandra, the couple claimed that after the war Mengele had signed a document renouncing all interests in the family industry at Guenzburg, and received only tiny remittances from them until his death.

He had lived very quietly in their neighborhood, a traditional area for German immigrants.

International Nazi hunters expressed considerable skepticism, pointing to numerous sightings after the supposed 1979 drowning. Beate Klarsfeld, who last week passed through Brazil after a fruitless search for Mengele in Asuncion, Paraguay, insisted in Rio de Janeiro that Mengele was living on a fortified farm on the Brazil-Paraguay border, receiving protection from the government of Paraguayan President Alfredo Stroessner.

Stroessner was scheduled to make an official visit to West Germany in July, but West Germany's ambassador to Paraguay announced today that the Paraguayan Foreign Ministry had requested a postponement.