The slim, dark-haired witness choked back tears as he recounted his abduction and months of torture in a clandestine prison. Around him, in a courtroom stilled by emotion, spectators wept and white-faced journalists scribbled notes with an urgency induced by shock.

Pablo Alejandro Diaz was one of 16 teen-agers picked up by the Army in the city of La Plata in 1976, allegedly for a minor matter. While in prison, he said, he listened and watched as dozens of other suspects were tortured, young girls were raped by guards and pregnant women were ignored as they gave birth inside bare cells. Of his group, Diaz added, he was the only survivor.

Last week, almost nine years after his abduction, Diaz had his chance to tell a panel of judges -- and a fascinated nation -- the details of his experience during Argentina's miltary rule.

"We were always blindfolded, but you could tell whether it was day or night," he said during a nearly unbroken, 90-minute account in the wood-paneled chamber of the federal appeals court here. "You could tell by the torture. When it was dark, when you couldn't sense the light, you would begin to hear the screams, the screams of the women, and you would know it was night."

Neither the prosecution nor the defense could summon up questions when the story was over. The presiding judge quickly called a recess to clear the court, and Diaz embraced his family as the journalists hurried out. The next day, his account was headlined in Buenos Aires' newspapers as if it were breaking news.

In this way, Argentines are reliving the darkest hours of their last military government through the public trial of nine former commanders. Day after day, witnesses ranging from students and poor workers to politicians and stone-faced generals are recreating the pain and terror of the military's four-year war against leftist opponents.

The three-week old trial is meant to judge the responsibility of the members of three juntas that ruled from 1976 to 1982 for abductions, torture, murders and other crimes committed by security forces. Five of the accused, including former presidents Jorge Videla and Roberto Viola, could be subject to sentences of life imprisonment.

The scope and often sensational content of the testimony, however, has made the trial into a kind of anguished national forum over Argentina's years of hatred and violence -- at once a platform for position-taking by politicians, a renewed battleground for the military and its opponents, and an emotional purgatory for dozens of victims allowed at last to tell their stories.

"For Argentines, the trial is acquiring a spectacular importance," said Emilio Mignone, a lawyer and leader of a major human rights group. "Every day the newspapers are full of the testimony -- and every day there is something new."

The divisions and terror of the past are threatening to explode into the turbulent present of Argentina's new democracy. The trial has provoked mass street demonstrations by military opponents and angry statements by retired officers against the government of President Raul Alfonsin.

Several witnesses have reported being attacked or threatened before their appearances, and a wave of violence by right-wing paramilitary groups has coincided with the first weeks of testimony. The incidents led Interior Minister Antonio Troccoli to declare last week that "a terrorist operation of the far right is under way" by "groups that were in charge of the dirty work of the repression."

Both in and outside the court, Argentines have been polarized between those who describe the military's campaign as a savage and illegal slaughter of suspected subversives and those who defend it as the necessary course for a government plunged by terrorist groups into an irregular civil war.

Defense lawyers for the commanders and sympathetic military witnesses have argued that the ruling juntas did not order illegal repression and were not aware of any widespread excesses, and that individuals who committed crimes were disciplined by the military at the time. "There were no innocent deaths, nor unjust acts," former Army commander Cristino Nicolaides declared. "This was an atypical war."

In contrast, chief prosecutor Julio Strassera has called journalists, politicians, and foreign officials to testify about conversations with military leaders in an effort to prove that the junta members knew the nature of the ongoing repression even if they did not explicitly order it.

The testimony of some prominent witnesses has seemed more related to the demands of present-day politics than the history of the past. A series of high-ranking officials from the populist Peronist government overthrown by the military in 1976 took the stand to insist that their party bore no responsibility for the repression, despite its formal orders to the military to "annihilate" terrorists.

During another session, several top leaders of the Peronist General Confederation of Labor, a strong opponent of Alfonsin's government, testified that despite their imprisonment, they were not aware of cases of torture and disappearance. The testimony provoked a public uproar in which the labor leaders were accused of courting the military in expectation of its eventual return to power.

By far the most dramatic statements, however, have come from a procession of citizens from all walks of life. Although few had direct contact with high-ranking military officers, the prosecution hopes through these accounts to build a piece-by-piece account of abuses so widespread as to indicate that the commanders could not have avoided general responsibility.

Thus, one Buenos Aires worker was called in last week to describe how he was abducted from his home early one morning, taken to a secret prison, and tortured with an electric prod. Just before 1 p.m., the man said, his torturer packed his tools and left, blandly remarking that he had finished his work shift for that day.

Other witnesses have told of a variety of abuses in secret prisons ranging from dunkings in water to rape, forced starvation and mock executions. Last Friday, a repentant policeman gave a detailed account of several gruesome murders, explaining that he decided to talk "so my children won't have to live through what has happened in this country."

Human rights lawyers argue that the weight of this grass-roots testimony will be overwhelming by the time the more than 2,000 expected witnesses have been called. "So many atrocities are being exposed, and so many people being named, that it is becoming obvious that there was a system of repression established here," said Mignone. "The trial is destroying the idea that there were only isolated excesses."

For the witnesses, the day of testimony in many cases has meant an enormous emotional release. "My husband always told me, despite all that had happened to us, that we had to go on living so we could tell," one former military prisoner told her lawyer before entering the court. "Now I feel that at last, I'm going to be able to do it."