THE "LAST" NAZI; The Life and Times of Dr. Joseph Mengele. By Gerald Astor. Donald I. Fine. 305 pp. $18.95.

SURVIVORS who came near Dr. Joseph Mengele at Auschwitz remembered very keenly the fresh scent of soap, the nimbus of cleanliness, that hung about him, so noticeable in that place of squalor and death.

As one of 22 "camp doctors," the young Mengele was a familiar and imposing presence at the railway sidings where floods of deportees had to be segregated. Those strong enough to perform slave labor were separated from those too old, feeble, sickly or young, and the latter were sped off to the gas chambers. Sometimes whistling an operatic aria, occasionally asking solicitously how this or that deportee had weathered the hard journey by cattle-car, Mengele with a flick of his finger or swagger stick would "select" those who would live from those who would soon be dead.

When Mengele, the "angel of death," was not playing God with new arrivals, he busied himself with medical experiments. He was a specialist in the study of twins and genetic deformities. The birth or arrival of twins at the death camp was a special event. Specimen infants marked for dissection would usually be killed by chloroform injections, directly to the heart. Sometimes interesting heads were shipped back to the medical institute in Frankfurt where Mengele had conducted his researches before the war. Mengele could be impatient. Eager to study the possible hereditary link between the deformed back of a father and the deformed leg of a son, he had the two executed on the spot and then hastily boiled so that their bones could be examined without delay.

Mengele's "selections" (who was to die, who to live) sometimes took on a special touch. On Yom Kippur, the JDay of Atonement, in 1943, 2,000 boys were assembled on the soccer field. Over one goal, a piece of wood was nailed at a certain height, and the boys herded under it. About half were too small, and "a wild scramble followed as SS troopers with dogs rounded up the petrified smaller boys," who were, of course, to be gassed.

The Yom Kippur "selection," Astor tells us, was not capricious. Mengele "knew that on the Day of Atonement Jews recite a prayer that tells of the flock passing beneath the rod of the shepherd -- the Lord -- who decides which will live."

The foregoing is a sampling, somewhat sanitized at that, of the cruelties that won Mengele his special infamy, and eventually led to a worldwide manhunt for him. The search ended last summer, a bit anticlimactically, with the identification of Mengele's scant and dusty remains in an obscure Brazilian grave. He had been dead for seven years.

Curiously, it had taken time for Mengele to become the hunted figure he was at the end. For some 15 years a his escape from Auschwitz, in the spring of 1945, he lived at various South American addresses, at times under his own name, even marrying the widow of a deceased brother.

Save for his evil acts, too well attested to by survivors to be seriously doubted, Mengele's story, like Eichmann's, has a certain drabness about it. This "angel of death" was the medium-sized son of a Swabian bourgeois family, manufacturers of farm machinery and solid citizens, who passed up a berth in the family business to study medicine. Like many restless young Germans of the 1930s, Mengele was drawn into various proto-Nazi organizations, first the so-called Steel Helmets, later the SA and finally the SS when war came. He fought briefly in the savagery of the Eastern Front -- Astor theorizes that the debasement of life and limb he witnessed there contributed to the callousness he displayed at Auschwitz.

WHAT SETS Mengele apart, aside from the aplomb with which he dispo many thousands, perhaps millions, to death is the utter mediocrity of his mind and spirit. In this informative account, Gerald Astor resolutely declines to elevate or sensationalize him into a storybook monster, a mad doctor, singularly abberational.

There was madness in Mengele's labors, to be sure. But Astor's theory is that it was the madness of a society; that the personal evil was rooted in a social climate in which the line we would draw between legitimate scientific medicine and quack, dehumanizing experimentation was wavily and cloudily marked. There was, in the medicine of the time, a widespread preoccupation with such odd specialties as "racial science," deformity, euthanasia, etc. Indeed, having finished his formal medical training, Mengele went to work in 1938 for Dr. Otmar von Vershuer at the Institute for Heredity and Racial Hygiene. (Racial hygiene! The name tells all.) Vershuer thereafter remained a sort of model for the young doctor, even after he had moved to the death amp duties.

What went on at Auschwitz, aside from the grim business of systematic killing, could be seen, so Astor suggests, as a grotesque but accurate caricature of these curious fixations of German medical science. Also in the background lay Hitler's promotion of "euthanasia," candidly aimed at weeding "defectives" from the "breeding stock," as one might cull out inferior show animals. Yet this medical quackery -- as it would be seen here and now -- abounded at the fringes of German medicine; it was respectable enough. One need not delve into the pages of Mary Shelley to account for a Mengele. Such at least is Astor's contention.

Of Mengele's long, nomadic postwar flight from German and Israeli pursuers -- Italy to Argentina to Paraguay and finally to Brazil, ending at last in his death by drowning or stroke on a beach near Sao Paolo -- there is little of great interest to be noted. The only savoriness in the tale of the fugitive years lies in the eas with which rumor, legend and disinformation came to be woven into the threadbare modicum of fact. But given Mengele's horrific reputation, it adds up to little -- far less, in any case, than in the dramatic fictionalized version offered in films like Marathon Man.

Astor's provocative argument is again that Mengele was not an aberration from, so much as a product of, his time and environment, that he reflected not personal but a "cultural and environmental sickness." "Mengele," he writes, "whatever his extreme characterological predispositions, was part of the mainstream of his nation and its prevailing moods, attitudes and indeed scientific philosophies . . . He was never a pariah in his land . . . He is not even that among many there today."

There is of course sound cautionary purpose in that argument. We are not, Astor urges, to make the perilous assumption that what happened in Germany could not happen again, and in any society. As prophylaxis against smugness and complacency, this is useful. As historical argument, it omits far too many distinctions to be finally persuasive. Societies have their particular histories and political chemistries. They are not sociological cross-sections but complex compounds, all discrete and quite different. Some are surely safer from such perversions as Nazism and its attendant bestialities than others. There are degrees of vulnerability.

Much the same must be said of Astor's insistence that Mengele be viewed not as a monster but as the personification of a certain current of prewar German medical science, admittedly gone far to seed. Maybe Mengele represented a heightened and heartless version of what some other doctors did or studied, but surely he was and did more. None of the 21 other camp doctors, even at Auschwitz, has been raised so high in the annals of infamy. Sadism on the Mengele scale merits a graver label than "extreme characterological predisposition." Moral monstrosity, so long as one is mindful of its metaphorical character, remains a useful category for making what limited sense we can of certain extremes of human behavior -- extremes that Mengele exhibited.

None of which is to dispute Astor's ultimate point. Self-satisfaction is the wrong response to such a terrible story. Better to come away with renewed wariness of the unchained human appetite, normal or abnormal -- and refreshed thanksgiving for the rule of law and for such civility and charity as mankind in its better moments has managed to achieve.