MADRID, Oct. 25 - After more than 40 years of searching, an international manhunt for Aribert Heim, a notorious doctor from the Nazi concentration camps and one of the most wanted Nazi war criminals, has zeroed in on a stretch of the Mediterranean coast of Spain, according to Spanish police officials.

Mr. Heim, born in Austria 91 years ago, is accused of torturing and killing hundreds of prisoners at the Mauthausen concentration camp in Austria in 1941 and 1942. The crimes for which he is sought include injecting gasoline into the hearts of victims, conducting operations on prisoners without anesthesia and executing prisoners just to record how long they took to die.

"The trial would be the most significant in the last 30 years," said Efraim Zuroff, director of the Israel office of the Simon Wiesenthal Center, which helps search for Nazi war criminals. "This case symbolizes the Nazi perversion of medicine and science, and the application of medicine to commit the most horrible atrocities."

Mr. Heim is second on the Wiesenthal Center's most wanted list of Nazi war criminals, after Alois Brunner, an assistant to Adolf Eichmann who is accused of deporting tens of thousands of Jews to Nazi concentration camps. Mr. Brunner is believed to be in Syria, and there is thought to be little chance of his being captured.

Spain has been a haven for Nazi war criminals since the end of World War II, when many were drawn here by the protection offered by the government of Francisco Franco, according to scholars of the issue.

Even after Franco died in 1975 and democracy was established, Spain's elected governments did little to cooperate with international searches for Nazi war criminals, those scholars said.

José María Irujo, author of "The Black List," a book about Nazis who fled to Spain, said in an interview that whole colonies of them lived here undisturbed for decades. "Many lived out their lives here, and died peacefully," he said.

"We are talking about hundreds of people," he said. "Spanish governments never did anything."

Dr. Zuroff of the Wiesenthal center said Spain had "a horrendous record on Nazi war criminals." But he added that under the government of Prime Minister José Luis Rodríguez Zapatero, a Socialist who was elected in March 2004, Spain appeared to have begun cooperating.

The Spanish police began searching for Mr. Heim over the summer in response to a request from the German government, which had detected large transfers of money to Spain from Mr. Heim's family in Germany, according to Dr. Zuroff and a Spanish police official.

The transfers, worth a total of about $400,000, were sent to Palafrugell, a town near Spain's northeastern coast, from 2000 to 2003, Dr. Zuroff said.

Other Spanish officials said their search for Mr. Heim was not limited to Palafrugell, but refused to specify where it was focused. They would say only that it spanned much of the Mediterranean coast, going at least as far south as Alicante, a section of southeastern Spain where many Nazis reportedly sought refuge after the war.

The developments in the search for Mr. Heim came 18 months or so after Germany set up a task force to find him. As part of the search, the Germans distributed a computerized rendering of what Mr. Heim, who is about 6 feet 3 inches tall and has a scar on his right cheek, might look like today and offered 130,000 euros, about $156,000, for information leading to his arrest. The Wiesenthal center offered an additional 10,000 euros.

There has always been reason to believe Mr. Heim is still alive, Dr. Zuroff said, because his million-euro bank account in Berlin has yet to be tapped by his children, who are free to do so if they can prove he is dead.

Mr. Heim has been a fugitive since 1962, when he fled his home in Baden-Baden, Germany, as the police were preparing to arrest him.

In 1979, a Berlin court declared him a major Nazi war criminal and convicted him in absentia of killing scores of prisoners at the Mauthausen concentration camp, some out of "pure boredom."