By JULIA PRESTON

                MEXICO CITY -- Bishop Samuel Ruiz Garcia, the Roman Catholic prelate who presides over an Indian-dominated diocese in southern Chiapas state, has stepped down as mediator in peace talks between the government and the Zapatista rebels.

          In a homily on Sunday, Ruiz, who has been mediator since the earliest days of the conflict in  1994, accused the government of "abandoning the path of dialogue" and promoting a "constant and growing aggression" against him and his diocese.

          His resignation represents a low point in the peace negotiations, which have been stalled since late 1996.

          Even though a cease-fire is in effect, factional village conflicts have proliferated since January as the government has stepped up a campaign to reassert control in regions where the Zapatistas  have grown strong.

          Government officials have accused Ruiz of being partial to the Zapatistas. In a recent speech President Ernesto Zedillo criticized "theologians of violence" who, he said, were aggravating the conflict, a comment that was widely understood as referring to the bishop.

          The government leaked to the press a letter from last year that another bishop in Chiapas wrote to Ruiz, questioning him about a flier circulating in the diocese that advocated armed violence. The government did not release a response in which Ruiz said the flier had not been written by           anyone in the diocese.

          "We have systematically opposed violence and no one among us preaches it or promotes it," Ruiz wrote.

          Government officials made no secret that they hoped to force Ruiz, who has been an outspoken critic of the government, to step aside. Several greeted his stepping down with delight.

          In his statement Ruiz noted that seven priests had been expelled from Chiapas in recent years, that four priests had been jailed on charges that were dismissed in court and that 40 churches had been closed or destroyed by pro-government factions.

          The Interior Ministry replied that it was "absolutely false" that there was persecution of the Catholic church in Chiapas.

          In his 38 years at the head of the Diocese of San Cristobal de las Casas, Ruiz's tenacious advocacy of Indian equality has earned him enemies within the government and among more conservative members of the Catholic hierarchy.

          In a rare statement Sunday, Pope John Paul II praised the work of Mexican bishops who work in Indian regions, although he did not mention Ruiz by name.

          At the core of the Zapatista movement, which began with a brief armed uprising, are a few hundred armed guerrillas hidden in jungle canyons. But it has spread into many Indian villages through unarmed grass-roots groups.