Pope John Paul II on Saturday warned followers of Marcel Lefebvre they will be excommunicated if they stay with the rebel prelate, but he promised the church will meet their traditionalist needs if they remain loyal to the papacy.

The Vatican announced Saturday that Monsignor Antonio de Castro Mayer, a Brazilian prelate who assisted Lefebvre in consecrating four traditionalist bishops, had been excommunicated.Lefebvre and the four bishops were excommunicated Thursday after Lefebvre defied the pope and performed the consecrations without his approval. The consecration led to the first church schism in 118 years.

"No one should ignore that formal adhesion to the schism constitutes a grave offense to God and leads to excommunication established by the right of the church," the pope said in his first public statement on the case since the consecrations in Econe, Switzerland.

In an apostolic letter to bishops, he urged Lefebvre's followers to "fulfill the serious obligation to remain united with the vicar of Christ in the unity of the church and not to continue to sustain (Lefebvre's) movement in any way."

To those wishing to remain faithful to the papacy, John Paul promised to guarantee their traditionalist needs, giving special attention to the 16th Century Tridentine Mass.

"To all those Catholic faithful, who feel close to some older liturgical forms and disciplines of the Latin tradition, I would like to express my will to facilitate their spiritual unity with the church, through the means necessary to guarantee respect for their just aspirations," the pope said in the letter, which was released in both Latin and Italian by the Vatican.

John Paul said he was setting up a special Vatican commission, headed by a cardinal, to "facilitate complete unification" with those Lefebvre followers who prefer to remain with the mainstream church.

He said the panel would seek to preserve "their spiritual and liturgical traditions."

Lefebvre and his followers reject many reforms of the Second Vatican Council, 1962-65, including the replacement of the Latin Mass with a simplified liturgy in the modern local language.

A few years ago, the Vatican issued a decree saying the Tridentine Mass could be celebrated with special permission.

The pope indicated he would permit wider use of the ancient liturgy, saying "a broad and generous application" of the decree would be allowed.

Lefebvre claims millions of sympathizers around the world. Vatican spokesman Joaquin Navarro said recently that Lefebvre's supporters numbered 80,000 to 100,000, but other Vatican officials have said about half a million people turn to his priests for various church functions.

John Paul said the church as a whole reacted with "great distress" to Thursday's consecrations, which "made useless years of efforts" to reach a settlement with Lefebvre's Piux X Fraternity.

"This despair is felt particularly by the successor of Peter (the pope) even if the number of people directly involved in these events is small," he wrote.

"This act of disobedience - which signifies the outright rejection of the Roman primate - constitutes a schismatic act," the pope said, noting that the prelates involved "have incurred the grave penalty of excommunication as foreseen under ecclesiastical discipline."

He called Lefebvre's action "contradictory" to the church traditions Lefebvre says he represents.

"One cannot remain faithful to tradition by breaking ecclesiastical ties with the man whom Christ himself, in the person of the apostle Peter, entrusted the ministry of the unity of his church," the letter said.