THE DISAPPEARED AND THE MOTHERS OF THE PLAZA; The Story of the 11,000 Argentinians Who Vanished. By John Simpson and Jana Bennett. St. Martin's. 416 pp. $17.95.

COVERING THE trial of Adolf Eichmann, Hannah Arendt not only discovered "the fearsome word-and- thought-defying banality of evil." She relearned a second awful lesson that her earlier reading of human history had taught her -- that "when visible, palpable, banal evil shows its face, few will speak out."

Argentina's holocaust was on a much smaller scale than Nazi terror -- approximately 11,000 people "disappeared" in the military's killing machine -- but the unheeded lessons of Nazi Germany were there to be learned all over again.

The horror of it all went unremarked. Evil was everywhere, every day. It was so normal, so accepted, so banal. And so few spoke out.

In his book Prisoner Without A Name, Cell Without A Number, Jewish journalist Jacobo Timerman, in relating his own experience as a hostage of the Argentine military over a 21/2-year period that began in a clandestine cell and ended under house arrest in his own apartment, noted that because the Argentine military did not render the bodies of Argentine Jews into soap, their compulsive anti- Semitism, which was manifested in exceptionally brutal and humiliating treatment of Jews, was denied by the leaders of the Jewish community. The Jewish community, like the rest of Argentina, behaved like an ostrich, demonstrating that had the military chosen to expand their scale of activities, they might have succeeded in emulating the Nazi war machine which so many Argentine officers, to this day, openly admire.

In a preface, the authors of this book, which is dedicated to "those who did not remain silent," try to place the horror in context and give a reading of it, measured against the scale of Nazi atrocities: "What happened in Argentina under the military government of 1976 to 1983 constitutes one of the worst examples of state repression since the end of the Second World War." And: "Comparisons with Nazism are dangerously easy to make, and made far too often, but what happened in Argentina in the years that followed (the military coup of 1976) was probably closer to what happened in Germany after 1933 than anything else in the Western world during the past four decades."

The authors, who were inspired to tell this story by reporting assignments for BBC television between October 1983 and April 1984 -- during which they covered the Falkland Islands War, which was the undoing of the military -- emphasize that Argentina under Jose Rafael Videla was worlds away from Cambodia under Pol Pot or Uganda under Idi Amin. "It is a highly developed country with an almost entirely European population, and a capital city which has a higher standard of living than that of many other capitals in what is loosely termed 'the West.' A street in Buenos Aires looks like any street in Brussels or Paris or London, except that the passers-by are likely to be better dressed."

Argentina is an elusive quarry, but the authors, who use a technique that is rather like a shooting script for a television program, capture its phantasmagorical atmosphere. They use general descriptive passages, like scene-setting camera shots, interspersed with close-ups in which specific people are interviewed, so that the story is carried forward in an episodic way. The book was not meant to be a comprehensive history. It is certainly not that, and it falls short of being "something of a study in political pathology," as they claim. "A mere recitation of the facts of what happened seemed to us insufficient," say the authors; "it was the experience that we wanted to convey."

THEY HAVE certainly succeeded in capturing the experience of the years of terror by telling the story through witnesses or particpants. They are shaky on a few minor facts, but the structure of their narrative is basically sound and they capture some nice nuances, like: "A distinctive quality of the Argentine terror was the strong element of the purely slapdash about it. You could be kidnapped and tortured, and most likely murdered, simply because you had the same surname as someone the military murder gangs were looking for, or you drove the same kind of car, or you lived nearby and must know something." Other fine touches in the book, which reveal the authors as not only shocked and fascinated by Argentina but also a little in love with this strange, unreal country and its maddening people, are to be found in their interviews with participants. Using an "I am a camera" technique, they run us through some telling vignettes of the few heroes of Argentina's mini-holocaust.

Among them is an interview with Tex arris, who was the human rights officer at the U.S. Embassy in Buenos Aires. He not only tried to save the innocent from the military's death machine but recorded the atrocities that almost all Argentines -- and a goodly number of his fellow diplomats -- did not want to see in a vast filing cabinet and got the information out. As the authors note, "It is even possible to maintain that the information from Tex Harris played an essential part in bringing the worst of the military's campaign to an end."

It is a little disturbing to observe that many of the people who did not remain silent were foreigners. Apart from a small group of outstanding Argentines, including a dark- horse politician called Raul Alfonsin, whose integrity was to play a major part in his election as president when the military decided to beat a hasty retreat from a multiple disaster (a destroyed economy, a ravaged polity and a lost war), the defenders of decency were all relatives of victims.

There was such lack of conviction in Argentina during the dark days when leftwing terrorism was countered by state-sponsored terrorism that the Mothers of Plaza de Mayo emerged as the conscience of the nation. They were despised by their fellow citizens from the start, as they are again today by many Argentines who think that they should keep quiet, now as then. But because motherhood commanded some respect, and because even one Argentine mother -- never mind several thousand of them -- is a force to be reckoned with, the Mothers took over the Plaza de Mayo, with all its symbolism associating it with the essence of nationhood, and managed to impose a reckoning with the truth.

This moving and remarkably inciteful book will help, like the chemicals working on a photographic print, to fix the truth that most Argentines, at one time or another, have tried to deny, and that they would, given any indication of the military's return, try not only to deny but to wipe out.

The book will not bring back a single one of the missing 11,000. But it will serve to point out that if more Argentines had spoken out, ordinary, everyday and unheroic goodness would have probably overcome the ordinary, everyday banality of evil.