More than 1,000 catholic priests, including some Americans, this week challenged Pope John Paul II's efforts to limit church political activism in Latin America, according to sponsors of the move here.

The challenge came in a strongly worded open letter handed to the pope early in his current visit to Brazil. The letter accused conservatives among the church hierarchy of condoning masacres carried out in the name of Christianity.

Sponsors of the challenge said Cardinal Paulo Evaristo Arns, archbishop of Sao Paula conveyed the letter to the pope. Copies made available to reporters in Mexico City.

The defiant priests said their own role in the transformation of Latin American society was "imperative" and "irreversible." Millions of Christians had already joined the "liberation struggle," and many priests had been killed as a result, they said in the letter.

"We are completely conscious of the risks we run and of the responsibility we accept," the letter said.

Despite the pope's frequent calls for unity, the text showed deep division within the church in the region where approximately half of the world's 700 million Catholics live.

Referring to ultraconservative and often ultra-Catholic political groups, the letter said, "The Latin American people find it repulsive that their assassins invoke their 'Christianity' to justify their killings, and that not a few bishops and even papal nuncios are their accomplices, at least in their passivity."

The document also reflected the growing militancy among liberal and leftist priests who support the "theology of liberation" and regard the church as the most powerful instrument for political and social change, if not outright revolution, in the region.

The pope attacked their political activism on his past visits to Mexico and Africa and again in Brazil, saying that clergy should be religious leaders and urging lay Catholics to involve themselves in political and social activism.

Fearing that his trip to Brazil, where the clergy is also deeply divided between conservatives and progressives would be a new occasion for rebuke, a reported 1,150 priests decided to try to preempt such a move.

"We think the pope has no clear notion of the realities of Latin America. He looks at us through Polish, anti-communist eyes," said one priest who helped draft the document. "We're telling him the political struggle here is irreversible. It's no good calling us to order and telling us to pray when there are bullets flying. There are two factions in the church and we're not moving back."

The document was delivered without signatures, which were deposited with a steering committee here in Mexico. According to one committee member, many bishops, including American bishops and priests from hispanic communities, signed or telephoned their support.

"The names will not be published to avoid repression from Rome," a Mexican bishop said. "We're not willing to provide the Vatican with an easy list of difficult people and have them investigate us as they have been doing with other dissidents."

Although the Latin American bishops' conferences in 1968 and 1979 produced compassionate manifestos giving clergy the green light to press harder for the rights of the poor, many more radical priest felt there was no avoiding outright political involvement.

"People in Latin America are not poor because of some natural destiny," the militant priests said in their letter to the pope this week. "Their cause is essentially political. They want the return of what has been stolen from them . . . by a minority that is substained by enormous political and economic power."

After offering a harsh historical analysis of the role of Catholicism in Latin America, the letter said that the time had come for the church to recognize its complicity in the "genocide" of the Indians of Latin America and the injustices imposed by the Spanish and Portuguese colonizers.

The letter included a long list of priests who were killed "as though they were common criminals" by rightist military or civilians in seven Latin American nations.

In recent years, according to the document, seven priests, including a bishop, were killed in El Salvador; 13, including a bishop, in Argentine; three in Chile; two in Brazil; three in Mexico, and two this year in Guatemala and in Bolivia.

In addition, the letter said, there are dozens of priests in Latin America who have been exiled, jailed or tortured.