MEXICO CITY -- In 1999, President Bill Clinton went to Guatemala and apologized. Just two weeks earlier, a United Nations truth commission found Guatemalan security forces responsible for more than 90 percent of the human rights violations committed during the country's long civil war.
Mr. Clinton's apology was an admission that the Guatemalan military had not acted alone. American support for Guatemalan security forces that had engaged in "violent and widespread repression," the president said, "was wrong."
But that long history of United States support for Guatemala's military, which began with a coup engineered by the Central Intelligence Agency in 1954, went unacknowledged during the genocide trial and conviction of the man most closely identified with the war's brutality, the former dictator Gen. Efraín Ríos Montt.
During a month of testimony before the three-judge panel that found General Ríos Montt guilty last Friday, the prosecution never raised the issue of American military backing in the army's war against leftist guerrillas. The 86-year-old former dictator barely mentioned the United States when he argued in his own defense that he had no operational command over the troops that massacred and terrorized the Maya-Ixil population during his rule in 1982 and 1983.
"This was a trial about Guatemala, about the structure of the country, about racism," said Kate Doyle, a Guatemala expert at the National Security Archive in Washington, an independent research organization that seeks the release of classified government documents.
Adrián Zapata, a former guerrilla who is now a professor of social sciences at the University of San Carlos of Guatemala, said that to prove a genocide charge, "it was not pertinent to point out the international context or the external actors."
But Washington's cold war alliance with General Ríos Montt three decades ago was not forgotten in the giant vaulted courtroom, where the current American ambassador, Arnold A. Chacon, sat as a spectator in a show of support for the trial.
"Part of the burden of that historical responsibility was that the United States tried to use Guatemala as a bulwark against Communism," Ms. Doyle said. "The U.S. played a very powerful and direct role in the life of this institution, the army, that went on to commit genocide."
Back in 1983, Elliott Abrams, the assistant secretary of state for human rights under President Ronald Reagan, once suggested that General Ríos Montt's rule had "brought considerable progress" on human rights.
Mr. Abrams was defending the Reagan administration's request to lift a five-year embargo on military aid to Guatemala. Brushing off concern from human rights groups about the rising scale of the massacres in Mayan villages, Mr. Abrams declared that "the amount of killing of innocent civilians is being reduced step by step."
Speaking on "The MacNeil-Lehrer Report," he argued, "We think that kind of progress needs to be rewarded and encouraged."
After the 1954 coup deposed the reformist President Jacobo Arbenz, the United States supported a series of military dictators, particularly after the victory of the Cuban revolution in 1959.
But an emphasis on human rights by President Jimmy Carter's administration led to the cutoff of military aid in 1977. Even though after 1981 the Reagan administration became intensely involved in supporting El Salvador's government against leftist guerrillas, and contra rebels against the leftist Sandinista government in Nicaragua, the Guatemalan government was so brutal that Washington kept it at arm's length for a time.
When General Ríos Montt was installed in a coup in March 1982, Reagan administration officials were eager to embrace him as an ally. Embassy officials trekked up to the scene of massacres and reported back the army's line that the guerrillas were doing the killing, according to documents uncovered by Ms. Doyle.
Over the next two years, about $15 million in spare parts and vehicles from the United States reached the Guatemalan military, said Prof. Michael E. Allison, a political scientist at the University of Scranton who studies Central America. More aid came from American allies like Israel, Taiwan, Argentina and Chile. In the 1990s, the American government revealed that the C.I.A. had been paying top military officers throughout the period.
"It was like a monster that we created over which we had little leverage," Professor Allison said.
During a hearing on reparations for the Ixil on Monday, the tribunal that convicted General Ríos Montt ordered the Guatemalan government to apologize in the main Ixil communities. President Otto Pérez Molina, a former general who served in the region but denies any role in atrocities, said he was willing to make the apologies.
Meanwhile, Guatemala's highest court has postponed rulings on a dozen procedural challenges from the defense that some experts say could ultimately annul the trial. The country's conservative leaders, represented by a business association known as Cacif, called on the constitutional court to "amend the anomalies" in the trial and complained that the world now viewed all Guatemalans as similar to Nazis.
For some in Guatemala, the virtual invisibility of the American role in the trial was disturbing.
"Who trained them?" asked Raquel Zelaya, a former peace negotiator for the government who now runs a research institute, referring to American support for the military. The trial seemed to be removed from all historical context, she said.
This article originally appeared in The New York Times.