The mutilated bodies of eight Peruvian journalists were discovered in a common grave yesterday by police outside of the Andean city of Ayacucho, 270 miles southeast of here.

The eight had been missing since Wednesday when they traveled to investigate a reported confrontation between peasants and Maoist guerrillas in a remote village north of the city.

Gen. Roberto Noel y Moral, Army commander for the region and chief of antiguerrilla operations in Ayacucho, was reported as saying that the journalists were killed by local peasants who mistook them for guerrillas. Two local guides, who were unharmed in the incident, have been detained for questioning.

The bodies of the journalists were found near the village of Uchuruccay, 50 miles northeast of Ayacucho. The journalists had been traveling on foot to Huaychau, a mountain village inaccessible by road where, according to Army reports, peasants last week killed seven members of the guerrilla group Sendero Luminoso (Shining Path).

Authorities estimated that the journalists were killed some time between Wednesday evening and Friday. Only two members of the group were positively identified on the scene. The others reportedly had been beaten beyond recognition.

The journalists were reporters and photographers for La Republica, Peru's largest circulation paper, El Observador and El Diaro, the two leading opposition dailies, and the news weekly Oiga.

The deaths were the highest numbers of civilian casualties reported since 1,500 Peruvian Army troops took control of eight central Andean provinces at the beginning of the year. President Fernando Belaunde Terry placed the provinces under military control after the guerrillas spurned his request to surrender.

The Army is coordinating antiguerrilla operations with special antisubversive police who have been fighting the group from its rugged stronghold in Ayacucho.

Progress against the guerrillas since the Army's intervention has been slow. Government forces have failed to draw Sendero Luminoso into an open confrontation, and the guerrillas have continued raids and assassinations in the countryside.

Sendero Luminoso, which is fighting to overthrow Peru's government in favor of a communist one, began its violence here two years ago.