One of the most bizarre manhunts of the 20th century is reaching a climax in the Parana River jungle on the border of Paraguay and Brazil. It is there that Dr. Josef Mengele, the so-called "angel of death" of Auschwitz, the Nazi concentration camp, reportedly resides in hiding. But there are strong indications that time is finally running out for Mengele, a fugitive for nearly 35 years.

A host of pressures for Mengele's extradition has been brought to bear during the past year on the government of Paraguayan President Alfredo Stroessner, who has been giving refuge to Nazi war criminals since he came to power in 1954. Last month, the Stroessner regime announced that it would ask its Supreme Court to annul Mengele's citizenship. In a regime as authoritarian as Stroessner's, such a request to the judiciary is tantamount to a fait accompli. Mengele has thus been declared persona non grata in his homeland of 20 years.

Stroessner's sudden change springs from the new Paraguayan desire for diplomatic respectability. One of the most hopeful trends in recent Latin American politics has been the efforst of dictatorships in Chile, Argentina, Brazil -- and now Paraguay -- to present themselves to the world as less repressive societies. The international impotence of authoritarian Brazil, for instance, contrasts sharply with the influence of relatively democratic nations such as Venezuela and Mexico, and this has not gone unnoticed by Latin American juntas.

Though the apparatus of fascism is still intact in the Latin American dictatorships, there has been a drop in the officially sanctioned kidnappings, torture and arrest of political opponents. Latin American juntas now hope that the United States and Western Europe will be more easily persuaded to offer the technological aid desperately needed for economic development.

From a stricly economic point of view, one of Paraguay's most desirable potential trading partners would be West Germany. (Stroessner, incidentally, is the son of a German immigrant.) But a thorn in West German-Paraguayan relations continues to be the German request for Mengele's extradition, officially "pending" since 1962, with Paraguayan officials pretending to know nothing of Mengele's whereabouts. The letter is a rather dubious claim, since the Nazi doctor has been seen in Paraguay by scores of witnesses and was tracked to a remote hideout on the Paraguayan-Brazilian border last winter by a team of British Broadcasting Corporation reporters.

As for Mengele himself, his fate is likely to become a bit precarious now that he has lost the patronage of his chief protector. Still, one should not underestimate the ability of Mengele's network of friends to find yet another Latin American dictator willing to take in the former Auschwitz doctor. Finding Mengele a new haven will not be made easier by the fact that the doctor's murderous career bears little resemblance to the fictionalized account of Ira Levein's book, "The Boys From Brazil." The novel was subsequently transformed by Hollywood into a science-fiction fantasy, in which Mengele conceived a plot to clone dozens of young Adolf Hitlers and unleash them on an unsuspecting world. The trouble with such dramatizations is that, by suspending reality, they tend to distract the public from the real facts about Mengele's grisly career.

As one of the chief physicians at Auschwitz, Mengele became steadily more drawn to a Faustian fate of complicity in the murders of hundreds of thousands. It was Mengele who separated arriving inmates by a flick of his finger -- right was the path for the healthier men and women fit to work; left meant the beginning of the inexorable march to the gas chamber.

But Mengele gained even greater notoriety from his experiments on twins. One of his favorite techniques was to separate twins who arrived at the death camp, feed them relatively well, then perform various experiments on them. When they had served his purposes, Mengele unceremoniously murdered them and dissected their corpses. It was all done in the service of propagating the so-called Aryan race, a project much favored by Nazi theoreticians.

Today Mengele remains both the most sought-after and the most elusive of Nazi war criminals. But whether he will ever have to face legal tribunals in Europe remains an open question. Certainly many in the Western world would like to deal with the "angel of death" in an extra-legal fashion. But whatever Mengele's ultimate fate, at least two hopeful signs can be detected from his loss of Paraguayan citizenship. The first is that Paraguay's increasing desire for diplomatic respectability may lighten the load of oppression borne heretofore by its citizens. The second is that there will now be a new discomfort in the serenity of Mengele's Latin American retirement -- the kind of discomfort the doctor so richly deserves.