Detective work by a dentist turned U.S. consul here has uncovered X-rays that finally should close the file on Josef Mengele, the most wanted Nazi war criminal.

Nine months after international forensic scientists stated that they were sure "within reasonable scientific certainty" that Mengele indeed had died in 1979 after a drowning accident on the Brazilian coast, they hardened the verdict today.

Diplomats say they have finally laid to rest doubts by all "reasonable and unreasonable investigators" who had favored "conspiracy theories" arguing that Mengele cunningly had faked his death in Brazil and moved on. Israel found the earlier findings inconclusive.

Forensic odontologist Lowell J. Levine, a consultant to the U.S. Justice Department, said in a formal report to Brazilian authorities that he was "absolutely certain" that the remains uncovered in a cemetery near here in 1985 were those of Mengele. His evidence was dental X-rays dating from March 1976.

The X-rays exhibit "multiple, unique and individual characteristics," said Levine and his Brazilian counterpart, Dr. Carlos Valerio.

The U.S. consul general in Sao Paulo, erstwhile dentist Stephen Dachi, and his deputy Fred Kaplan unearthed a clue in the yellow pages of an old telephone directory.

Although investigators had determined that Mengele had lived in Brazil, they could not say with certainty that he had died here. There were no fingerprints, and the only surviving dental records were from the 1930s.

Dachi uncovered the X-rays last Friday, acting on a hunch after Brazilian police had failed to trace doctors and dentists mentioned in a diary compiled by Mengele covering his years in Brazil.

Mengele's protectors in Brazil had concealed the diary from police and later sold it to a West German magazine. The Justice Department's Office of Special Investigations translated it into English.

Mengele's diary made a single reference to a root canal treatment in 1978 by a "Dr. Gama in Sama" but the single Dr. Gama uncovered by police was the wrong man.

"We were riding back from talking to the wrong Dr. Gama, kind of down because we had struck out," said Dachi. Then they looked again at the diary transcript. Although "Sama" appeared several times in the diary, there is no such place in Brazil. Dachi noticed a number of abbreviations and guessed it meant Santo Amaro, a residential suburb.

In an old directory, Dachi and Kaplan found the name of Dr. Hercy Gonzaga Gama Angelo, a root canal specialist. Gama's records confirmed that in December 1978 he had treated a "Pedro Hochbichler," who gave his address as Mengele's last known hideout. The alias had been used by Mengele.

The dentist who had sent "Hochbichler" to Gama produced a dental chart and an envelope with eight X-rays and confirmed that dental bridges and crowns found in the skull were his own work.

"I never expected anything like this," said the dentist, Dr. Kasumasa Tutiya, in a phone interview. "He was just one of my patients."

"When Dr. Tutiya dropped those X-rays on the table it was like winning the lottery," said Dachi. "In 40 years, no one has ever found a single X-ray of Mengele. We found a man who had eight."

Dachi, formerly an oral pathologist, also had provided the tooth work in an early phase of the probe, linking evidence of a jawbone infection to Mengele through testimony of a couple who had sheltered him.