Perhaps it began the day newly installed Secretary of State Alexander M. Haig Jr. suggested that four American churchwomen murdered by Salvadoran security forces may have inadvertently caused their own deaths.

"Some of the investigation," Haig told a congressional hearing, "would lead one to believe that perhaps the vehicle in which the nuns were riding may have tried to run a roadblock, or may accidentally have been perceived to do so, and {that} there had been an exchange of fire."

It was March 18, 1981, and President Ronald Reagan had been in office less than two months. Haig had already said that "international terrorism will take the place of human rights in our concern," and his statement about the churchwomen appeared to be the proof: In El Salvador the Reagan administration was worried about Marxist insurgency, not the behavior of a friendly government at war.

For 12 years, opponents of U.S. policy in Central America accused the Reagan and Bush administrations of ignoring widespread human rights abuses by the Salvadoran government and security forces and of systematically deceiving or even lying to Congress and the American people about the nature of an ally that would receive $6 billion in economic and military aid.

Their views appeared to be vindicated last week, when a three-man, U.N.-sponsored Truth Commission released a long-awaited report on 12 years of murder, torture and disappearance in El Salvador's civil war. The commission examined 22,000 complaints of atrocities and attributed 85 percent of a representative group of them to Salvadoran security forces or right-wing death squads. It blamed the remainder on the guerrilla Farabundo Marti National Liberation Front (FMLN).

After the truth commissioners appeared before the House Western Hemisphere subcommittee, Chairman Robert G. Torricelli (D-N.J.) vowed to review for possible perjury "every word uttered by every Reagan administration official" in congressional testimony on El Salvador.

The Reagan administration is making no apologies. Elliott Abrams, who held two assistant secretaryships in the Reagan State Department, said "the administration's record in El Salvador is one of fabulous achievement," and attacks on it are "a post-Cold War effort to rewrite history." He dismissed Torricelli's threat as "McCarthyite crap."

Indeed, an examination of the public record fails to turn up statements that could be described as blatant lies. In speeches, interviews and countless appearances before Congress, a parade of Reagan and Bush officials vigorously defended U.S. policy in El Salvador, asserted that human rights was a top U.S. priority and insisted that the Salvadoran government's record was one of steady improvement.

"We are not saying that the human rights problems of the country have been resolved," Thomas O. Enders, assistant secretary of state for inter-American affairs, told the Senate Foreign Relations Committee during one typical exchange on Feb. 8, 1982. "To the contrary, we believe massive problems remain. But we see progress in the downward trend of noncombatant deaths since early 1981."

But if there is no "smoking gun," there is overwhelming evidence, both in the officials' own documents and in their public statements, that if they did not know details about human rights abuses, it was because in many cases they chose not to know. The information was there.

In May 1980, for instance, when Jimmy Carter was still president, security forces seized documents implicating rightist leader Roberto d'Aubuisson in the murder of Archbishop Oscar Arnulfo Romero, fatally shot in March 1980 while saying Mass in the chapel of San Salvador's Hospital of Divine Providence. In a report two years later, the House Intelligence subcommittee on oversight and evaluation expressed outrage that the materials "had been ignored by policy makers, who felt they had no immediate use for them, but more importantly by the intelligence community."

In the fall of 1981, Army Brig. Gen. Fred Woerner supervised preparation of a joint U.S.-Salvadoran internal military "Report of the El Salvador Military Strategy Assistance Team," which noted that "the {Salvadoran} armed forces are reluctant to implement vigorous corrective actions for abuses in the use of force."

It further found that "the absence of a functioning chain of command is compounded by the predisposition toward violence by some security force personnel, as well as their demonstrated susceptibility for being co-opted by the right."

The military "as an institution, has demonstrated a remarkable capacity for tolerating unprofessional and improper conduct . . . protecting its own, ignoring, suppressing, covering up or, at most, imposing minor punishment," the report said. "Unabated terror from the right and continued tolerance of institutional violence could dangerously erode popular support to the point wherein the armed force could be viewed not as the protector of society but as an army of occupation."

And again, one year later, Ambassador Deane Hinton, in a speech before the American Chamber of Commerce in San Salvador, told his audience that "since 1979 perhaps as many as 30,000 Salvadorans have been murdered, not killed in battle, MURDERED {emphasis in the original}."

"Is it any wonder that much of the world is predisposed to believe the worst of a system which almost never brings to justice either those who perpetrate these acts or those who order them?" Hinton asked. The Reagan administration disavowed his remarks, saying the speech had not been cleared by the White House.

Critiques that came from outside the administration were most often ignored or dismissed as unwelcome: "The embassy never liked to hear the bad news," said Americas Watch counsel Jemera Rone, who worked in El Salvador in 1985-90. "So they attacked the messenger."

One reason so many people found it hard to believe that U.S. officials could not have known more about rights abuses and acted more aggressively to curb them is that the United States was deeply involved in running the war, from intelligence gathering to strategy planning to training of everyone from officers to foot soldiers.

By 1982, U.S. military advisers were assigned to each of the six Salvadoran brigades, as well as each of 10 smaller detachments.

A senior U.S. official admitted he and others could have known much more than they did, but "these were the guys we were working with day in and day out, and we did not want to create a hostile situation." Besides, he said, "we were here to fight the guerrillas, they were the enemy, and we did not go around investigating our friends."

Sometimes officials painted the messenger as a communist dupe or even a sympathizer. In this way Abrams, as assistant secretary of state for human rights and humanitarian affairs, dismissed reports published in The Washington Post and the New York Times of massacres by Salvadoran army soldiers of hundreds of people in the village of El Mozote in December 1981.

"We find . . . that this is an event that happened in mid-December," Abrams told the Senate Foreign Relations Committee in February 1982 during testimony to support certification requirements that the Salvadoran government was improving its human rights record. The incident "is then publicized when the certification comes forward to the committee," he added. "So, it appears to be an incident which is at least being significantly misused, at the very best, by the guerrillas."

Throughout the war years events like El Mozote, the archbishop's murder and the so-called "nuns case" were hotly debated between the Reagan and Bush administrations and their opponents in Congress and the rights community. Neither side disputed that such incidents had occurred, but there was no agreement on their scope, details or the degree of complicity of the Salvadoran security forces.

In this area the Truth Commission's report is blunt and unequivocal in its assertions and heavily buttressed in most cases by new details that reflect extensive interviews both with victims' families and members of the armed forces.

El Mozote, the report said, was the work of the U.S.-trained Atlacatl Battalion, part of a days-long search-and-destroy sweep known as "Operation Rescue." In fact, the report said, the soldiers massacred more than 500 in six villages.

In El Mozote, where the identified victims exceeded 200, "the men were tortured and executed, then the women were executed and finally, the children," the report said. Soldiers killed one group of children, it added, by spraying machine-gun fire through the doors and windows of a tiny building where they were penned up.

During the 1982 hearing, Enders and Abrams said they had sent two military officers into the area to check the massacre reports. They said the investigators talked with nearby peasants but could not reach the village and concluded that the incident could not be confirmed. Enders cast doubt on the reports, noting that the total population of El Mozote was 300 people, and "there are manifestly a great many people still there."

The Truth Commission report erases this objection, saying that large numbers of refugees were living temporarily in El Mozote when the soldiers arrived. Fixing blame, it said, was no problem, since there were plenty of witnesses: Atlacatl did it, the report said, in a "deliberate and systematic manner."

"Despite the public denunciations of the events and the ease with which the facts could be proved," the report said, "Salvadoran authorities did not order any investigation and have consistently denied the existence of a massacre."

In case after case, the report is equally categorical: "Ex-Maj. Roberto d'Aubuisson gave the order to assassinate the archbishop," the report said. He "issued precise instructions to his bodyguards, acting as a 'death squad,' about how to organize and carry it out."

In the nuns case, the report said, the killers set up the roadblock outside the airport two hours before the murders, intending to waylay the four churchwomen as suspected guerrilla sympathizers: "Then-Col. Carlos Eugenio Vides Casanova, among others, knew that members of the National Guard had committed the murders on orders from superiors," the Truth Commission said. "The subsequent concealment of the facts had the effect of prejudicing the process of judicial investigation."

As defense minister in the mid-1980s, Vides Casanova later became one of the pillars of U.S. policy in El Salvador. Also named by the commission in the nuns case coverup was Lt. Col. Oscar Edgardo Casanova Vejar, who participated in the Salvadoran side of the Woerner report, which said there was never "any serious discussion" between U.S. military personnel and their Salvadoran counterparts about right-wing terror or institutional violence.

The Truth Commission's findings appear to have put to rest some arguments that simmered for years, but the relatively peaceful postwar ambience in which it worked contrasts markedly with the often chaotic conditions of the early 1980s.

Haig took office six weeks after the churchwomen's murder and a week after a guerrilla "final offensive" had left the future of the U.S.-supported junta in doubt. The Carter administration had suspended U.S. aid because of the nuns case but resumed it during the guerrilla offensive.

Salvadoran security forces had been killing large numbers of civilians for more than a year, and U.S. officials had been able to do little about it. Haig may have appeared flip and unconcerned, but the Reagan administration, like Carter's immediately before, was groping for a policy in an uncertain and threatening environment.

Even after the conflict had stabilized in late 1981, officials said they often had an imperfect knowledge of human rights abuses. Enders, now a partner at Salomon Brothers in New York, said in a telephone interview that while "we all suspected d'Aubuisson" in the Romero case, "we never quite proved it." And even with FBI involvement in the nuns investigation, "we had no evidence that directly implicated Vides {Casanova}."

Enders said he was never sure exactly what happened in El Mozote, and cable traffic shows that the U.S. Embassy consistently felt casualties in El Mozote were "highly exaggerated." A subsequently declassified message of Feb. 10, 1982, said embassy personnel "have not been able to visit El Mozote because it is once again in rebel hands."

Abrams was more blunt about official ignorance: "Anybody who thinks you're going to find a cable that says that Roberto d'Aubuisson murdered the archbishop is a fool."

In fact, there are at least two declassified cables from the embassy that make precisely this claim. One, dated Nov. 19, l980, mentions d'Aubuisson as the leader of the Romero plot. The second, on Dec. 21, 1981, speaks of "a meeting, chaired by Maj. Roberto d'Aubuisson, during which the murder of Archbishop Romero was planned. During the meeting, some of the participants drew lots for the privilege of killing the archbishop."

But neither Enders nor Abrams had any doubt about the wisdom of U.S. policy in El Salvador: "It was clear from the start that we were engaging in supporting a security force that was doing violence to their political opponents as well as to their enemy," Enders said. "We knew we were going to get tarred, but we engaged so we could control and reform them while we helped them stave off the threat to their country."

By 1982, the Reagan administration saw U.S. involvement as a choice between what Abrams in a recent interview called "two terrible alternatives: We can walk away from it, or we can stick around."

They stuck around, and by 1984 the number of civilian deaths began to drop precipitously. This, said Abrams and Enders, is the proof of the policy. Not so, said Cynthia Arnson, associate director of Americas Watch and author of a book on the Reagan administration's Central American policy.

"It became clear that the effort to win the war was going to require far greater resources than the administration had imagined," Arnson said. "Therefore it was necessary to seek some improvements in the human rights situation."

On Dec. 11, 1983, Vice President George Bush visited San Salvador and read the riot act to President Alvaro Magana: "Your cause is being undermined by the murderous violence of reactionary minorities," Bush said. "These cowardly death-squad terrorists are just as repugnant to me, to President Reagan, to the U.S. Congress and to the American people as the terrorists on the left.

"If these death squad murders continue, you will lose the support of the American people," Bush said. Bush's aide, Lt. Col. Oliver North, handed Magana a list of nine names of death-squad leaders.

Although the violence declined sharply, the gesture backfired. Two of eight officers on the list -- National Police Lt. Col. Aristides Alfonso Marquez and Jose Ricardo Pozo -- remained on active duty until this January, nine years after they were identified. Marquez tried to get a visa to stop in the United States on his way to a diplomatic posting in Canada, which was to be his punishment. Salvadoran sources said the CIA gave him the visa, although the embassy denied it.

The civilian on the list, d'Aubuisson's security chief, Hector Antonio Regalado, was hired by the Drug Enforcement Administration's San Salvador office in 1987 as a shooting instructor. After finding out who he was, the United States pressed for his arrest in the Romero killing. He was held for a night, then released for lack of evidence.

On Nov. 16, 1989, the years of careful effort to reform the Salvadoran armed forces collapsed when, amid the most intense guerrilla offensive of the war, soldiers of the Atlacatl Battalion murdered six priests, their housekeeper and her daughter in a predawn raid at the Jesuit-run Central American University.

Ambassador William Walker was widely reported as claiming that the guerrillas were responsible for the murders, but he said in an interview this was "simply not true. What we were saying was that we did not know -- that it could have been the military, that it could have been the FMLN, and we were still seeking a breakthrough."

What came across at the time, however, was confusion and a belligerent defense of the government and armed forces: "Management control problems exist in a situation like this," Walker told a news conference after the murders. "And it's not a managment control problem that would lend itself to a Harvard Business School analysis."

On Jan. 2, 1990, Walker told Rep. Joseph Moakley (D-Mass.) in Washington that "anyone can get uniforms. . . . The fact that they {the killers} were dressed in military uniforms was not proof that they were military." The same day that he met with Moakley, U.S. Army Maj. Eric Buckland, a military adviser in San Salvador, told his superiors that a Salvadoran army officer had named Military Academy chief Col. Guillermo Alfredo Benavides Moreno as the ringleader in the Jesuits' killing.

Benavides was sentenced in 1991 to 30 years in jail for the killings, but the Truth Commission said it regarded the conviction as "unjust," since Benavides was following orders from the army's chief of staff, Col. Rene Emilio Ponce, and his deputy, Col. Juan Orlando Zepeda.

The commission "considers it unjust," the report said, that Benavides and one other officer are "still in jail, while the intellectual authors of the assassinations, and those who gave orders for the killings, go free." Ponce, a favorite for years of the U.S. Embassy and the Bush administration, submitted his resignation as defense minister March 11.

Gugliotta reported from Washington, Farah from San Salvador. Staff researcher William Hifner contributed to this report.