STOCKHOLM -- He turned 79 last month. Or would have, were he still alive. In the vast, terrifying space between those two possibilities -- his life or his death -- dwell Nina Lagergren and Sonja Sonnenfeld.

Raoul Wallenberg, vanished hero of the Holocaust, is Nina's half-brother and Sonja's obsession. Both are in their seventies. Both have spent their last years in a haunted, restless search for a man who disappeared into the iron bowels of the Soviet gulag 46 years ago. Both believe they are nearing the answer. But both fear they are running out of time.

Now there is new hope. The abortive coup that shook Moscow last month sent tremors all the way to the most protected inner sanctum of the old regime -- KGB headquarters. The official now in charge, Vadim V. Bakatin, is the same man who two years ago, in his previous post, granted researchers for the family unprecedented access to Soviet prison records.

For 12 years the Soviet Union insisted it had no knowledge of Wallenberg and nothing to do with his disappearance. For 34 years after that, it insisted he had died of a heart attack in a Moscow prison in 1947, two years after his arrest. Only now are the Soviet authorities willing to pursue the possibility that the second statement was as much a lie as the first.

Bakatin has promised the KGB's active cooperation in searching its massive archives. And he has pledged something more important as well: to lift the vow of silence that prevents retired KGB officers and prison-keepers from divulging what they know about Wallenberg's fate.

This could be the moment Nina and Sonja and their two closest associates -- Guy von Dardel, Nina's brother, and Per Anger, Wallenberg's former diplomatic colleague -- have long awaited. Or it could be the latest in a cruel series of cold trails and false hopes.

The search for Raoul Wallenberg is part detective story, part human drama. It is the story of a man who challenged and overcame one totalitarian nightmare only to be swallowed whole by another. He was supposed to vanish down Stalin's dark memory hole, but his deeds were so extraordinary that his memory would not die. Now the system that sought to bury him is itself on its deathbed and yielding its secrets.

But it is also the story of four elderly people who are struggling against time to find the truth. Ask them and they will say that, against all odds, they are searching not just for the truth, but for the man. Raoul Wallenberg, each one insists, is not dead.

"Of course we want to believe it," says Per Anger, 77. "But there are so many facts to base it on. If you are strong mentally and physically you survive, and Raoul was very strong. These prisoners are kept without stress, not too much fat in the diet, no alcohol, no tobacco. You are not allowed to die."

"I don't say he could still be alive today," says Sonja. "I say I know he is alive. We want to know his fate, but that's not enough. We also want him free."

Years of Stonewalling Nina Lagergren is a thin, placid, 70-year-old woman who wears an air of shy dignity like a protective cloak. She answers questions slowly these days, and her voice often falters -- not from emotion, although it seems always just beneath the surface, but from a desire to find the correct word and to be clearly understood.

She is a true believer in her half-brother, who was sent to Budapest by Sweden in 1944 at the behest of the U.S. government, and she describes in loving detail his inner strength, wit, warmth and idealism. The qualities that compelled him to go there 47 years ago to rescue tens of thousands of Hungarian Jews, to bribe, cajole, charm, shame and threaten the Nazis and their henchmen and to pull victims out of Adolf Eichmann's death trains and away from execution squads -- these same qualities, she believes, would have seen him through the years of the gulag. She cannot believe the slender, sparkling, athletic young man she knew could have died of heart failure at age 34.

In the 1980s Raoul Wallenberg became a venerated public figure, his exploits known throughout the world. But for more than 30 years, his mother and stepfather, Maj and Frederik von Dardel, worked in virtual anonymity with only the help of a few family friends. The Swedish government, tainted by its own neutrality during the war, was reluctant to challenge or offend the new superpower to the east.

The von Dardels died in February 1979, within two days of each other, their quest incomplete. Nina watched their struggle, shared some of the work and the agony, and took over after their deaths. "My mother never lost hope that Raoul was alive," recalls Nina, "but of course it was torture for her."

He disappeared in January 1945, just after the Red Army seized Budapest from the Nazis. He was traveling that day with a Soviet military escort north from the capital to meet with the Soviet commander and outline his plan to provide shelter and food for the city's survivors. He told the last friend who saw him, "I do not know if I am a guest or a prisoner."

One month later, Maj von Dardel received a note from the Soviet ambassador in Stockholm. It read: "Your son is in Russia. All is okay."

Other captured diplomats were freed, but Raoul Wallenberg never came home. It would be two years before the Soviets commented again. Then in August 1947, Deputy Foreign Minister Andrei Vishinsky reported to the Swedish government: "As the result of thorough investigation it has been established that Wallenberg is not in the Soviet Union and that he is unknown to us."

For years Soviet commentators suggested that Wallenberg had been ambushed outside Budapest by Hungarian fascists and had never reached Soviet military headquarters. What really happened, as the Soviets now concede, is that Wallenberg and chauffeur Vilmos Langfelder -- who also vanished -- were detained by Soviet military authorities and flown to Moscow as suspected spies.

A retired Hungarian translator identified only as Istvan K., in an interview with a Budapest newspaper two years ago, said she had been flown to Moscow as a prisoner along with Wallenberg. She recalled that he was pessimistic: "He did not expect anything good, because when the plane took off he said, 'Take a good look, because you will never see Hungary again.' "

The Swedish government quietly requested, but never demanded, information from Moscow. At one point in the late 1940s, Per Anger was put in charge of the search for his friend. He says he ran up against a wall of denials not only from Moscow but from officials in Stockholm as well. He became so frustrated that he finally insisted on being removed from the case.

"They didn't want to upset the big neighbor too much," says the 72-year-old Guy von Dardel of the Swedes. "You can see them saying, 'Well, for the good of the country we have to sacrifice one citizen.' But when that citizen is your own half-brother, then of course one feels a bit bitter."

Nonetheless, as prisoners of war were gradually released in the late '40s and early '50s, reports from those who had seen or heard of the Swedish diplomat began trickling out of the gulag. It became clear that he had been imprisoned, and Sweden began to press for an answer.

It finally came in February 1957 in a memorandum written by Deputy Foreign Minister Andrei Gromyko. After "a careful investigation of the archives" and interrogations "held with many persons," Gromyko wrote, the Soviets had found no one who knew anything about Wallenberg. They had discovered one document, however -- a handwritten report on plain paper from Col. A.L. Smoltsov, head of the Lubyanka Prison medical service, to Minister of State Security Victor Abakumov:

"I am reporting that the prisoner Wallenberg, who is known to you, died suddenly last night in his cell -- probably from myocardial infarction {heart attack}." Below is a notation: "Have personally informed the Minister. Order was given to cremate the body without autopsy. ... {signed} Smoltsov."

Gromyko added that since Smoltsov had died in 1953 and Abakumov had been executed a year later for "criminal activities," further investigation was impossible. "The conclusion should be drawn that Wallenberg died in July 1947," said Gromyko with finality.

The problem with the Soviet explanation was that many of the sightings of Wallenberg occurred long after his purported death. Imprisoned biologist Alexander A. Smovsky claimed he met Wallenberg twice in Siberia in 1949. Some 15 witnesses said they had contact with him at Vladimir Prison north of Moscow in the 1950s or '60s. A Swiss citizen testified that in 1954 he exchanged messages with Wallenberg at Vladimir by tapping on the wall. An Austrian swore that in early 1955, he shared a cell with Wallenberg. A Muscovite released in 1977 called his daughter in Israel and mentioned meeting Wallenberg in a Moscow prison.

By the mid-1980s, Sweden had compiled more than 20,000 pages of testimony involving some 3,000 names and witnesses. About a third of the information dated from 1979 or later. How much was true and how much wishful thinking or sheer imagination, no one could say.

Still, the Soviets stood firm, plugging leaks as they appeared in the stone wall of denial. In 1961 a Soviet colleague told the eminent Swedish professor of medicine Nanna Svartz that he knew about Wallenberg and that he had been very ill and was in a mental hospital.

Svartz reported the conversation to Swedish Prime Minister Tage Erlander, who wrote an urgent message to Nikita Khrushchev asking to send a Swedish doctor to see Wallenberg. There was no reply from the Soviets. Later Svartz's colleague insisted she had misunderstood him and that he knew nothing of Wallenberg.

Sometimes the signals were more Kafkaesque. Karl Gustav Sweingel, a Swedish social worker living in Berlin, recalled a conversation in 1966 with an East Bloc "representative" who hinted he was prepared to arrange an exchange involving Wallenberg and a Swedish spy named Stig Wennerstrom. Later the man told Sweingel, "I want to tell you that Wallenberg doesn't exist." Sweingel, using his notes from the meeting, says he replied, "But this doesn't mean he's dead." And the man answered, "Yes, you're right." The discussions went no further.

The Tug of a Hero Sonja Sonnenfeld joined the search around 1980. A translator and a legal assistant, she had read about Wallenberg and found herself drawn to a man of such heroic character. Nina spoke to her constantly about her half-brother and let Sonja read his letters. Soon Sonja, who is Jewish, was hooked.

"I felt an obligation," Sonja recalls. "I had to stay and I had to stick it out. I felt I owed it to him. Maybe I'm obsessed, but I can't give up hope as long as there is hope to do something for him personally. I must get him out."

They make an odd couple. Where Nina is shy, dignified and distant, Sonja is aggressive, passionate and personal. Nina is indecisive, Sonja determined. Nina instinctively avoids publicity -- she refused to be photographed for this article -- while Sonja believes the press is crucial to the search.

Sonja became the unpaid secretary of the Raoul Wallenberg Society in Stockholm. She brought new life to the search -- and something more. From the constant trickle of people returning from the gulag, she found a confidential source, she says someone with contacts in the large network of Soviet and Eastern European dissidents who in turn knew someone else who claimed to have seen Wallenberg alive in the early '80s.

Sonja believes her source, though she concedes it is largely an act of faith. And she has persuaded Nina, Guy and Per to believe as well. "He's hidden in a camp of silence, a place where people are said to be dead," Sonja says.

Then two years ago, the thaw melting the Soviet system unfroze the Wallenberg case as well. Officials invited Nina, Sonja, Per and Guy to Moscow.

On a crisp October morning, the four were received at the Soviet Foreign Ministry. There was a deputy foreign minister, a senior diplomat and two tight-lipped KGB men -- "the stone faces," Sonja calls them.

First they were shown the original Smoltsov document. Then the Soviet authorities sprang a surprise: They produced a stack of Wallenberg's personal belongings -- his diplomatic passport, diary, address book, notebooks, registration card and cigarette case, along with a pile of dollars and old Hungarian pengos. They claimed these had been recently found in a sack in some forgotten corner of the prison archives.

"Nina didn't make much fuss of it, much to the Soviets' distress," Sonja recalled. "They had expected tears of appreciation and gratitude." Indeed, when the officials asked Nina to sign a receipt in Russian for the items, she refused.

"It was quite incredible, handing me these items," says Nina. "They gave me the feeling they must have much more. Everyone told us the Russians never destroy files and documents. They must be somewhere in the KGB."

As far as the Soviet authorities were concerned, the meeting was over. But Wallenberg's people had further demands. They presented a list of about 20 witnesses they wanted to interview, and they asked for permission to visit Vladimir Prison and check its records. Guy von Dardel got permission directly from KGB chief Bakatin, then interior minister.

The Soviets proceeded to collect statements from the alleged witnesses -- all of whom denied any knowledge of Wallenberg. "The fact of Wallenberg's death is irrevocable," Nikolai Uspensky, a Europe specialist at the Foreign Ministry, told reporters.

Nonetheless, the Soviets sanctioned the establishment of a 10-member commission of experts consisting of five Soviets and five Westerners. It was chaired by Irwin Cotler, a prominent human rights lawyer from Montreal. In August 1990, the group was given unprecedented permission to enter prisons and search records.

The group spent eight days at Vladimir, where it found no concrete evidence of Wallenberg's presence. Nonetheless, the members concluded that there was "incontrovertible evidence" that Wallenberg did not die of a heart attack at Lubyanka in July 1947. They also concluded that, contrary to Vishinsky and Gromyko's memorandums, the Soviets never actually investigated Wallenberg's fate at Vladimir or anywhere else -- no records were searched, no prisoners or officials interviewed.

"Wallenberg was a non-person for us until 1988, an unmentionable," Alexander Semyonov, a senior Vladimir prison official, told the commission. "We could not even talk about him, let alone investigate whether he was imprisoned here."

The commission members examined 104,000 prison registration cards and discovered that many of the foreign prisoners had been given fake names or numbers. Their grim conclusion: "If Raoul Wallenberg's prison registration card is a numbered one, or registered under a false identity, it makes its discovery -- and the discovery of his fate -- well-nigh impossible."

Nonetheless, Vadim Birstein, a dissident biologist and prison expert serving on the commission, was able to trace Wallenberg's movements up until his purported death in 1947. He concluded that Wallenberg was confined to Cell 121 or 123 at Lubyanka when he arrived in February 1945 and that two months later he was transferred to Lefortovo, Cell 203. In 1947 he was returned to Lubyanka.

There the trail runs cold. But something extraordinary happened in July 1947, notes Birstein. Every person who had ever been a cellmate of Wallenberg or the chauffeur Langfelder was interrogated on the 22nd, questioned about everything they knew of the two men, then "strictly forbidden to utter the names of Wallenberg or Langfelder at any time in the future."

Maj. Boris Solovov, deputy security chief, examined the files of Wallenberg's former cellmates and interrogated many of them. He is retired and living in Moscow. According to Birstein, he won't speak without KGB permission. After Bakatin resigned as interior minister last year, Birstein and other researchers were prevented from continuing their work. But with Bakatin's accession to the post of KGB chief last month, Swedish officials and Wallenberg supporters believe the gates will again be opened.

"I think the situation is more promising now than it's ever been," says Guy von Dardel, a retired physicist who spends much time traveling to Moscow to work on the case. "This has been a miraculous year from our point of view. That the same man who helped us with Vladimir now heads the KGB seems almost like a miracle to me. And since miracles have happened, there is no reason not to believe in the ultimate miracle -- that perhaps Raoul is still alive."

Two weeks ago Bakatin's KGB disclosed five new documents on Wallenberg. According to the Tass news agency, one was a letter dated June 12, 1957, from the chief of the KGB to a senior Foreign Ministry official saying documents on the case had been destroyed on order of the Ministry of State Security, which existed from 1946 to 1954. None of the newly released documents provided evidence on his fate.

"We have no foundation for reaching any conclusion that Mr. Wallenberg was alive after 1947," the new KGB deputy chief, Nikolai Stolyarov, told reporters. He promised further cooperation -- including the right to interview witnesses like Solovov -- but warned that the KGB is not yet prepared to throw open its files to the public.

"Let us suppose that tomorrow we opened wide all the archives," he said, according to Reuter. "Can you imagine what an orgy {of violence} could take place in our very precarious society? To open up the archives now is a bit too early."

Time for Answers It is not too early for Nina Lagergren and Sonja Sonnenfeld. For them time is a luxury. They are encouraged by the new thaw in Soviet attitudes. And they are tantalized by reports that former prisoners have begun trickling back to the Baltic states. Some were arrested 50 years ago. All were believed to have died long ago. Now the dead are returning. And if they are alive, Nina and Sonja argue, then perhaps Raoul Wallenberg lives as well.

All have been questioned. So far none has produced a new clue to his whereabouts or his fate. Meanwhile, every week or so, there is another phone call or a fax to the Wallenberg Society here from someone who has heard something, seen something or believes something. The search continues.

Next August Raoul Wallenberg turns 80, or would were he still alive. There will be worldwide commemorations. And there is the hope that there will be, by then, a resolution.

Sonja has lost none of her exuberance, but she lives in fear -- fear that the trail will lead nowhere, that the truth lies among anonymous ashes in an unmarked grave. She also fears that Nina and the others are losing confidence in her, that they doubt her source and her faith. "Nina always believed I would find Raoul," she says. "She never says it, but I'm afraid she feels I have let her down."

For Sonja the looming 80th birthday is a reminder that time is running out. "We have to find the truth now because I'm so afraid this will not be passed on to another generation. Young people have to earn money. They have no time for this search. Yes, sometimes I'm afraid it will all die with us."