Nicaragua's newly elevated Roman Catholic Cardinal Miguel Obando y Bravo called for national reconciliation and peace this morning at an open-air mass attended by a smaller than expected crowd, estimated at 30,000 people.

Obando, the most prominent critic inside Nicaragua of the country's leftist Sandinista government, generally steered clear of politics during a 15-minute homily. The mass was the first that he has celebrated here since his investiture as cardinal on May 25 in Rome.

He pledged to share his country's "happiness, its sufferings, its difficulties and its aspirations," and urged his listeners not to lose hope despite such problems as a civil war and a stumbling economy.

"Let us construct a peace, a true peace, where we Nicaraguans see each other as brothers," Obando said.

The head of the National Bishops Conference, Bishop Pablo Antonio Vega, made several veiled criticisms of the Sandinistas in an address shortly before Obando's homily. In addition, occasional shouts of "Down with communism!" from the crowd, and participants' comments to reporters, made it clear that the gathering was viewed by some as a demonstration against the government.

"The people are Catholic. They don't want totalitarianism," a 27-year-old truck driver said in a comment typical of those heard in the crowd.

Obando's elevation from archbishop made him the first cardinal in Nicaragua's history and Central America's first native-born cardinal. Church officials, some diplomats and Nicaraguan opposition politicians have predicted that this newfound prestige will give Obando additional clout in criticizing the government on such issues as the military draft and what the church views as the Sandinistas' efforts to build a regimented society.

Obando's own call for reconciliation reflected differences between his views and those of the government. The church has urged the government to open peace talks with the anti-Sandinista guerrillas known as contras and has offered to serve as mediator, but the government has refused.

The turnout at the mass was disappointing for the church, which had estimated beforehand that well over 100,000 would attend the service held on an athletic field at a local high school. "It was less than we hoped," a Nicaraguan priest said. He put the crowd at 20,000, while journalists' estimates generally ranged between 20,000 and 40,000.

A much larger number turned out last night and lined a parade route to welcome Obando back to Nicaragua. Journalists estimated that at least 100,000, and perhaps as many as 200,000, people were on hand. It took Obando six hours to make the nine-mile trip from the airport to his residence, edging forward through the throng on the back of a pickup truck dubbed the "Cardinal-mobile."

The mass today, and most of the procession last night, was peaceful. But the Interior Ministry reported today that 11 policemen were injured and two government vehicles were "semidestroyed" during a confrontation at the airport with people who were awaiting the cardinal in a parking lot that was supposed to be closed to the public.

The crowd there threw rocks and plastic bags filled with soft drinks at the police, who used fire hoses to disperse the gathering. Eight youths were detained by police following that incident and another in which the crowd tore down part of a Sandinista billboard, according to a church spokesman, Msgr. Bismarck Carballo. Obando said at the start of his homily that he hoped the detained youths would be released soon, and the Catholic Radio reported that at least one was freed this morning.

Apart from these difficulties, the police appeared to have made a point of not interfering with the procession and mass.

In addition, despite media censorship here, the procession and mass both were broadcast live nationwide on Catholic Radio and on radio stations in Costa Rica and Miami. Managua's two morning newspapers, which are both pro-Sandinista, ran front-page stories today on the cardinal's return.

Obando often smiled broadly during the mass, which was interrupted repeatedly by chants of "Obando, Obando!" and "Long live Catholic Nicaragua!"

Bishop Vega, the church's most outspoken critic of the Sandinistas, made several statements apparently aimed at the government in his speech. He said Nicaraguans have been "victims of partisan divisions."