CHACALTE, Guatemala (AP) _ When the armed men came, 9-year-old Roberto Sanchez hid with his sister under their bed. His mother was shot dead, apparently shielding the children with her body.

He fled while flames destroyed their house, killing his little sister.

It is the sort of story that has become routine as Guatemalans piece together the bloody history of a three-decade civil war that ended in December. But here, survivors say, it was not the army blamed for the butchery.

It was the rebels.

A new project to exhume mass graves at Chacalte is the first probe into guerrilla war crimes since forensic anthropologists five years ago started digging up the secret graves left over from the war.

``This was a dirty war,'' said Sanchez, who on his way to adulthood learned much about the raid from older villagers over the years.

Survivors say at least 120 people were killed in the attack on Chacalte in June 1982 at the height of the war.

It is a bitter lesson for some human rights activists accustomed to blaming the army alone for the war that claimed an estimated 140,000 lives, not including 40,000 people who disappeared and were never heard from again.

``The army committed most of the violations, so it is not good to blame the guerrillas and the army in the same way _ but if this massacre was done by the guerrillas, they should take responsibility for it,'' said Rosalina Tuyuc, a human rights campaigner elected to Congress last year.

Survivors blame the Guerrilla Army of the Poor for the massacre. Most say it apparently was retaliation for the community's collaboration with the military's armed civilian patrols, which later earned international condemnation for their human rights abuses.

Chacalte, 150 miles northwest of Guatemala City, commands a strategic position within the Ixil Triangle, one of the most bitterly contested war grounds of Guatemala.

``The army was trying to widen its network of control and the Army of the Poor was frightened of losing its influence,'' said an Italian Roman Catholic priest who came to the region in 1983. The massacre ``was an exemplary punishment,'' said the priest, who identified himself only as Father Rosalino.

Since a peace treaty in December, the Army of the Poor has been transforming itself into a political party.

Arnoldo Noriega, spokesman for the former rebels, denied that his group massacred civilians at Chacalte. He said the rebels got into a shootout with civilian patrols.

But the forensic evidence tells a different story.

Since mid-August, a team sponsored by the Roman Catholic archbishop's human rights office has been digging in what was once the heart of the village. It is now a cornfield in the misty mountain forest.

In two weeks, the team has uncovered 53 bodies in seven mass graves.

``Here we've found everything. Men, women and children killed by bullets, machetes and burned,'' said Mariana Valdizon, a member of the forensics team.

The survivors dispersed after the massacre, but some have come back since Chacalte was resettled six years ago. They often stop by the site to help the team dig and tell of their memories of the massacre.

``We base our exhumation on the testimonies of survivors,'' said Federico Reyes, coordinator of the forensic team. ``We are doing our best to discover the truth.''

Almost every day since the exhumation began, Caterina Perez has walked two hours along a muddy path from her home to watch the work, hoping that her husband's remains will be uncovered.

On Sunday, she recognized the green sweater and blue pants cut off one of the skeletons. Evidence of a back problem in the skeleton added weight to her identification.

``I was made too sad thinking of him buried in this way,'' she said.

The village's poor residents were, in theory, fertile ground for recruiting support and sympathy for left-wing rebels.

But Demetrio Cojti, a Mayan academic, said the mixed-race rebel leaders often failed to respond to the needs of the Indian population.

``The guerrilla leadership wanted to impose socialism and did not include the decolonization of the indigenous populations among their demands,'' he said. ``This was their biggest error.''

Sanchez said he might have understood the rebel raid ``if they had carried out a clean war and only killed the patrollers'' linked to the army. But ``they killed old people like my mother, and children like my little sister.''