RIO DE JANEIRO, Nov. 5 - After years of characterizing the human rights violations that occurred in Chile under the dictatorship of Gen. Augusto Pinochet as "excesses" by individual officers rather than a deliberate government policy, the Chilean Army reversed course on Friday and acknowledged that it must bear collective "institutional" blame for such abuses.

"The Army of Chile has taken the difficult but irreversible decision to assume the responsibility for all punishable and morally unacceptable acts in the past that fall on it as an institution," the current army commander, Gen. Juan Emilio Cheyre Espinosa, wrote in an essay published by La Tercera, a daily newspaper in Santiago, the capital. "Never and for no one can there be any ethical justification for human rights violations," he said.

An official commission is readying a comprehensive report, expected to be made public this month, on torture and other systematic human rights abuses by state security and intelligence agents during the Pinochet dictatorship. Human rights groups estimate that about 4,000 people were killed after General Pinochet took power on Sept. 11, 1973, in the American-supported coup that overthrew Chile's elected left-wing civilian president, Salvador Allende. Thousands were tortured, jailed, forced to leave the country, stripped of their jobs or sent into internal exile.

The "new vision" that General Cheyre announced Friday clashes directly with the views General Pinochet has always expressed. Now 88, ailing and under almost permanent investigation in connection with human rights abuses that occurred during his 17 years in power, General Pinochet maintains that he and other members of the military high command never issued orders to eliminate opponents of their dictatorship and that any abuses were the work of a few rogue officers.

He and his lawyers had no immediate response to General Cheyre's statement, which could encourage the filing of new legal charges against him. Though General Pinochet has been stripped of his immunity from prosecution in two major investigations, he has avoided a trial so far because doctors found him to be suffering from senile dementia.

"It's going to be hard for Pinochet to keep arguing that he had no clue, no sense, of what was going on, and that all the atrocities were due to a few bad apples," said José Miguel Vivanco, a Chilean who is director of Human Rights Watch Americas. Two former navy commanders close to General Pinochet criticized General Cheyre's declaration.

"It seems to make no sense to me," Adm. Jorge Arancibia said. The other former navy chief, Adm. Jorge Martínez Busch, said he was "not in agreement with this vision, because simply put, that's not how it was." He added: "I categorically reject there was any such policy of state, as some maintain. Responsibility is always individual."

Human rights groups generally expressed skepticism of General Cheyre's timing and motives. They said that while any admission of guilt was welcome and overdue, they would only be satisfied if the army provided names of all in its chain of command who had participated in rights abuses, so that prosecutors could act on the information.

"We worry that this might be just another trick to assure impunity for human rights violators," Lorena Pizarro, president of the Group of Relatives of the Detained and Disappeared, said in a telephone interview. "Some defense lawyers are already arguing that since the violations were committed by the state, you cannot hold individuals responsible for that policy."