Thousands of persons chanting, "The disappeared -- tell us where they are," marched on the vacant congressional palace today in the latest upsurge of Argentina's expanding controversy over the military's elimination of terrorists and other domestic opponents in the late 1970s.

Surrounded by heavily armed police, barricades, armored cars and circling helicopters, a crowd estimated by Argentine news services at 3,500 paraded after a 24-hour demonstration and vigil near the central Plaza de Mayo.

Police sealed off the protest, organized by families of missing persons, shortly after it began yesterday afternoon, preventing the demonstrators from reaching either the plaza, with its presidential palace, or the steps of the ornate Congress building.

The march was the latest of a recent series of demonstrations over Argentina's disappeared, and it came as national attention focused on the painful and politically preeminent question of how to resolve the legacy of the military's violent internal repression.

Military spokesmen have suggested in recent days that the armed forces will soon issue a lengthy justification of their extralegal abductions of thousands of persons -- most of whom were tortured and killed while the government denied knowledge of their whereabouts -- and decree an amnesty for all those involved in the disappearances.

The swelling human rights movement here, although largely unsupported by traditional political leaders, has vowed to reverse any such action and has demanded that military leaders be held responsible for each of the estimated 6,000 to l5,000 who disappeared.

Many Argentines, rocked by the recent discovery of unmarked mass graves and widely publicized protests from many European countries about loss of their citizens here during the repression, appear to be responding for the first time to what many are calling the nation's greatest national tragedy.

"There is a basic soul-searching here of genuine guilt," said Marshal Meyer, an American who has lived in Argentina for more than 20 years as the director of a Jewish cemetery. "What is lacking," he added, "is the expiation of that guilt. This is still a country that has never faced up to the truth."

Yet, at times in recent weeks, Argentina has seemed to be a country possessed by its disappeared. The polemics are found not only in the newly awakened mass media, but also heard in bars and at newstands and in the trains hauling commuters. The theme is denounced by an angry military and handled delicately by a majority of frightened civilian politicians. But it is everywhere.

In a downtown cafe, a young government clerk said, "There were rumors, but we never knew. Now I can see that we can live in a country where war can happen and we will never know."

For many politicians and intellectuals, the history of the military's repression has exploded from a shell of euphemisms to become the primary issue of an already turbulent society, demanding painful explanations of past inaction and silence.

In a private home, a retired Army officer spoke about his personal role with remorse. "There were no white hats," he said. "There were those who tried to control it, but there was no control. It is something we will live with for all our lives."

Both the military government and its opponents have warned that the issue of the disappeared is the greatest obstacle to the military's plan to leave power -- hence politicians and officers are reported to be hurriedly negotiating the blanket amnesty to try to close the issue.

What is at stake is more than the possible punishment of a few high officers, who have already promised to return the country to democracy, Meyer and other human rights advocates here say. Instead, they say, what is being tested is a society's ability to discover and accept its own history -- and the consequences of failure, it is argued, are incalculable.

"We are facing something that is very dangerous, not only for us, but for the civilized world," said Eduardo Pimentel, a leader of the Argentine Permanent Assembly for Human Rights. "If a crime of this magnitude goes without investigation, in a sense sanctioned or tolerated, it will be a blow against human rights everywhere."

For six years of the military's rule after a 1976 coup, it appeared that the cases of the disappeared might not be officially admitted or publicly discussed at all.

Even before taking power, the military had begun fighting then-active groups of urban leftist guerrillas with their own tactics: small, heavily armed squads that struck unexpectedly, extracted intelligence ruthlessly, then summarily executed their captives. The role of the then-ruling Peronist movement in this initial violence has never been clarified, either.

After the military takeover, armed forces officials admit privately, the operation slipped completely out of control. Human rights groups charge that not only terrorists, but also thousands of other persons suspected of supporting them or simply suspected of knowing them, were picked up -- as were families and bystanders -- and brutally disposed of. Prominent labor leaders turned up missing, along with dozens of journalists. More than 100 children under the age of 10 disappeared, human rights activists say.

All along, the military denied any knowledge of the missing persons, their whereabouts, or even the activities of the paramilitary groups. And most Argentines turned their heads the other way.

Only a few persecuted journalists and a handful of relatives and human rights activists spoke about the missing in Argentina until this year. Then came the military's disastrous invasion of the Falkland Islands, and with its defeat, an outpouring of criticism of the armed forces' rule.

Soon several former government officials called for investigations of some of the most notorious disappearances, involving loyal diplomats who tried to curtail some military activities. Then, the brother of a witness in one of the cases disappeared and was later found dead, setting off a storm of controversy.

Six weeks ago, human rights groups began to publicize discovery of unmarked graves, linked to individual cases of the disappeared and, through court records and witnesses, to military operations. Hundreds of graves were counted. Judges began hearing new cases. And as new reports came in, the number of graves rose to well over 1,000.

Now the struggle for national opinion is on. The military has publicly reacted strongly, blaming the new uproar on allegedly renascent subversion. The graves, although linked to the Army in official records, have been officially described as burial sites for paupers and the unidentified.

The problem of the disappeared, announced Navy Commander-in-Chief Ruben Oscar Franco recently, "should not be resolved. There was a terrorist violence that had to be confronted by the armed forces. This violence was confronted by the armed forces and it is a triumph of the nation over terrorism."

"They will never win in the end, because there must be justice," answers Nora de Cortinas, a leader of the Mothers of the Plaza de Mayo group. Cortinas lost a son, a 24-year-old medical student, on April 15, 1977. "I want him back alive, because he was taken alive," she said. "If not, I want justice for the people responsible."

Between those positions is a spectrum of confused, resigned or angry opinion. Many people here, according to church and human-rights activists, say they are learning of the depth of the tragedy for the first time.

"They have heard it all before but they never believed it or wanted to believe it until now, when there is an air of scandal and the military is in shambles," said Meyer, who added that he had been approached by many such people in the large congregation he serves as a rabbi. "They don't really know what they should think or what they should do. But there is an 11th Commandment for Argentines: 'Don't get involved.' "

"After the World Cup in 1978 the soccer championship hosted by Argentina , people I knew just seemed to forget about it," said the government clerk, who like many, is still fearful enough to ask that she not be quoted by name. "Then I started reading the papers about the graves and all of the abuses. It makes me feel that no one in government here can ever be believed. Now I know that whenever there is a government, they will be doing something I don't know and lying about it."

There are others who knew but said little or nothing. They are intellectuals, journalists, teachers and politicians who welcomed the military coup, who feared the guerrillas and wanted the armed forces to eliminate them.

"Foreigners will probably never understand it," a prominent intellectual priest here said. "But what we had here was a war. I don't know of a country that has gone to war with guerrillas without torture. There are always excesses. But the only answer, without forgetting, is to erase the accounts and begin anew."

His argument is one of the most common in Argentina, perhaps still largely accepted by a majority of the people, some human rights leaders concede. The crowning point of this view -- and to many its greatest attraction -- is that Argentina is not, as international organizations have charged, the site of an appalling crime, and cannot be lumped in with Stalin's Soviet Union and Nazi Germany.

"This is the same as what happened when the United States fought communism in Vietnam," said the priest. "And how many of your military were put on trial for that?"

In dozens of interviews and conversations here, a deep popular cynicism about Argentina's institutions emerges clearly. There is little hope, even among activists, that much can now be done; there are no precedents or goals to spur a commitment to an uncompromising view.

Instead, the military's overwhelming power to prevent strong action is cited, along with history: a brutal 19th century dictator, Manuel de Rosas, who remains a hero to many Argentines; a systematic extermination of Argentina's Indian tribes still described in history books as a glorious national victory.

There is a one-act play now being performed in Buenos Aires that until months ago would never have been allowed on a public stage. It is about an old judge, and his secretary's first morning on the job. The two consider a pleading from relatives of one of the missing, and the secretary heatedly remonstrates with the judge when he decides to summarily dismiss it.

As the judge persists in his decision, bloodied human bodies surreally begin to descend from the ceiling of his office and roll out of the doors of his closet. Ignoring them, he orders an assistant to drag the now-hysterical secretary from his office. The play ends as actors imitating corpses silently fill the office, writhing and open-eyed, while the judge obliviously returns to his paperwork.

At one recent performance, the drama ended to emotional applause and cheers from an audience of several hundred. Many stood to applaud the actors, while others remained more quietly in their seats.

As the house lights went on, one woman could be seen quietly crying.