Peruvian President Alan Garcia, in a move to assert his authority over the military and reorient counterinsurgency efforts, has fired the chairman of the Joint Chiefs of Staff, Air Force Gen. Cesar Enrico.

The decision was made last night at a Cabinet meeting and announced in a communique.

The communique said that " . . . to bring about a substantial change in the antisubversive strategy, the government has decided to change the chairman of the Joint Chiefs of Staff." The communique specifically criticized the secrecy that has surrounded the fight against Maoist Shining Path guerrillas, as well as mounting casualties and disappearances in the conflict.

The communique also said that three Army officers and a driver had been implicated in the killing of seven persons whose bodies were found in a clandestine cemetery in Ayacucho, 450 miles southeast of Lima. Investigations were continuing into another incident in which 69 peasants allegedly were killed by soldiers, it added.

The military shake-up provided the first opportunity in Garcia's six-week-old government to redefine military tactics and tackle the issue of human rights abuses. During the past three years, more than 6,000 persons have died in incidents connected with the guerrilla conflict, and atrocities have been reported on both sides. Human rights groups have gathered data on more than 1,000 disappearances.

On Aug. 14, Garcia said in a televised speech that "in defense of democracy, we are going to act energetically against those who accept violence, but we will not permit excesses." The president added, however, that the armed forces as a whole were not implicated in abuses.

Garcia appointed a six-member commission to investigate reports of human rights abuses, review the cases of 1,500 suspected terrorists awaiting trial and eventually make contact with the guerrillas to see if negotiations might end the bloodshed.

The confrontation with the armed forces was sparked by a fresh round of charges that security forces had committed human rights violations in the central Andes region around the guerrilla stronghold of Ayacucho. On Aug. 29, seven bodies were found at the clandestine Pacayacu cemetery. All seven persons previously had been arrested by security forces, according to the attorney general's office in Huanta.

Then, on Sept. 11, reports reached Lima of a massacre of 69 peasants in the community of Accomarca, Ayacucho, a month before. There is evidence that the Accomarca community had supported the guerrillas.

Garcia gave the military deadlines to provide full reports on the incidents. The first deadline ran out yesterday, with the ouster of Enrico. A second deadline on the Accomarca incident is set for Sept. 18.