Opposition leaders gathered at a Santiago cathedral, and thousands of Chileans met in churches, schools and homes today for a Catholic Church-sponsored "Day of Fasting and Prayer" that became a quiet protest against Gen. Augusto Pinochet's crackdown on the opposition.

Called by Santiago Archbishop Juan Francisco Fresno, the fast day drew residents of dozens of poor neighborhoods to local chapels for services and "reflections" on the government crackdown that began with the declaration of a state of siege Nov. 6.

"Let us ask the Virgin to be with us now, when we have been so badly beaten down in the last days," said Rev. Guido Peetres raising his arms during one service in the poor neighborhood of La Legua.

"The people are living in slavery," sang his congregation to the accompaniment of a guitar. "The people call for freedom."

Dissident labor leaders, journalists, students, professionals and politicians used the event for rallies that mixed prayer with protests against military rule. This evening, opposition political leaders attended a mass at Santiago's cathedral. Police did not intervene in the gatherings, mostly conducted inside churches, and no violence was reported by late today.

The church assemblies came after two weeks of confrontations between Pinochet's government and the Catholic hierarchy and reinforced what appeared to be mounting political tension across the country. Opposition leaders said they hoped the religious gatherings would help ignite a wave of public resistance to the government meant to climax in nationwide demonstrations early next week.

Today, authorities acknowledged terrorist attacks for the second straight day and closed down university campuses in two cities to head off unrest.

In the most serious incident reported since the state of siege was declared, officials said an armed group attacked a Marine detachment guarding a bridge outside the city of Talcahuano and killed one soldier.

In addition, authorities reported that a car bomb was discovered and deactivated early this morning near the Ministry of Defense in Santiago. Other bombs exploded in the port city of Valparaiso, officials said. A car bomb had exploded outside a police barracks in Valparaiso yesterday, wounding two officers.

Classes at several campuses of the Catholic University in Santiago were suspended today after students vowed to go ahead with the university's elections, which were banned under the state of siege. Authorities also decreed an early end to the school year at the University of Concepcion, a focus of antigovernment activity.

The church meetings today focused in large part on a pastoral letter by Fresno that criticized the state of siege and accompanying offensive against opposition media, political parties and the church. In many neighborhood churches, parishoners spent the day analyzing the government crackdown and drawing up their own statements, which were read at community masses this evening.

The archbishop's letter and convocation for the fast was read in all Santiago churches last Sunday after the government censored several church statements, banned a series of Catholic meetings and prohibited the head of the church's human rights organization from reentering Chile after a trip abroad.

Fresno, a conservative who frequently has sought to avoid public standoffs with Pinochet's government, appeared to accept one government measure today by naming a new leader of the church's human rights-oriented Vicariate of Solidarity to replace banned Spanish priest Rev. Ignacio Gutierrez.

Church officials said that the naming of the new vicar, Rev. Santiago Tapia Carvajal, represented a reversal of Fresno's previous refusal to accept the expulsion of Gutierrez, an aggressive leader who angered the government with harsh public denunciation of its human rights record.

However, church sources said that the archbishop had reiterated his intention to continue the church's action on human rights in a private letter dispatched yesterday to Interior Minister Sergio Onofre Jarpa.

"He is going to be loyal, loyal, three times loyal to what the church has been doing in human rights," said one ranking cleric who asked not to be named.

Fresno suddenly indicated his continued irritation with the government by refusing to release a letter he had received from Jarpa explaining recent government measures. Jarpa had said publicly he hoped Fresno would release the statement, but church officials said the archbishop decided not to comply because of the government's recent censorship of the church.

Government officials strictly limited media coverage of the fast today but otherwise did not openly criticize the church's activity.