MEXICO CITY - Just before leaving office, the administration of President Vicente Fox has quietly put out a voluminous report that for the first time states unequivocally that past governments carried out a covert campaign of murder and torture against dissidents and guerrillas from the late 1960s through the early 1980s.

The 800-page report is the first acceptance of responsibility by the government for what is known here as the "Dirty War," in which the police and the army are believed to have executed more than 700 people without trial, in many cases after torture. It also represents the fulfillment of Fox's vow when elected in 2000 to expose the truth about an ugly chapter in Mexico's history.

Human rights experts said the special prosecutor who issued the report, Ignacio Carrillo Prieto, had not succeeded in prosecuting the officials responsible for the crimes, notably former President Luis Echeverria.

Instead of being announced at a public event, the report was posted on the Internet late Friday night.

The report relies on secret military and government documents that Fox ordered declassified. It contains chapters on the killings of student protesters in Mexico City in 1968 and 1971 and a brutal counterinsurgency operation in Guerrero state, where military officers destroyed villages suspected of helping the rebel leader Lucio Cabanas and tortured their inhabitants.

The document trail makes clear that the abuses were not the work of renegade officers but an official government policy.

The events took place during the administrations of Gustavo Diaz Ordaz, Jose Lopez Portillo and Echeverria.

The Security Department kept the presidents informed about many aspects of the covert operations.