SAN FRANCISCO — At Most Holy Redeemer Catholic Church in the Castro, this city’s largest gay district, about 20 of the faithful gathered for 8 a.m. Mass recently, clustering in the middle pews. Led by a visiting priest from nearby Oakland, the parishioners joined in celebrating the 30th anniversary of a gay couple.


The celebration was not out of place in San Francisco, at least not in those parishes that have somehow bridged the colossal gap between their gay members’ lives and church doctrine. But the appointment of a new leader of the archdiocese here — Bishop Salvatore Cordileone, 56, a rising conservative who led the fight against same-sex marriage in California — has many gay and lesbian Roman Catholics worried about the fate of these sanctuaries.


At a cafe where some of the parishioners met after Mass, many said they would take “a wait-and-see” attitude toward Bishop Cordileone, who has led the Oakland Diocese for the past three years and is scheduled to be installed as archbishop here on Thursday, the feast of St. Francis, San Francisco’s patron saint. Some expressed hope that in getting to know his followers here, Bishop Cordileone would come to see things their way.


Others were more defiant, saying nothing would shake their faith.


“In a sense, I am glad that the church is sending the top guy that they have — the top antigay — because it means that we, as a community of Catholics, have done something good to deserve attention,” said George Woyames, 68, who added that he was raised as a Roman Catholic but became committed to the religion only after joining Most Holy Redeemer in 1987.


Bishop Cordileone was one of the leading proponents of Proposition 8, which banned same-sex marriage in November 2008 by defining marriage in California as between only a man and a woman. The proposition, which voters endorsed after hard-fought campaigns on both sides, overturned a decision just months earlier by the California Supreme Court that legalized same-sex marriage. But legal challenges to the ban have been working their way through higher courts since then.


Bishop Cordileone is also the chairman of the United States Conference of Catholic Bishops’ subcommittee for the defense of marriage, whose mandate is “promoting and defending the authentic teaching of the church regarding the nature of marriage as a covenant between one man and one woman.”


In The Voice, the newspaper of the Oakland Diocese, Bishop Cordileone said it was “too early to say” what he would focus on as the archbishop of San Francisco.


“I need to get a better lay of the land,” he said.


Asked what is the one thing people in San Francisco should know about him, Bishop Cordileone, who has also been active against the death penalty and in favor of an immigration overhaul, said he was “not a single-issue person.”


But experts said the appointment of a figure so strongly associated with opposition to same-sex marriage as archbishop of San Francisco, the heart of the gay rights movement, inevitably carries a message from the Vatican. In keeping with the growing conservatism of the Catholic Church in the United States, Bishop Cordileone’s installation comes as the Supreme Court prepares to weigh in on the issue of same-sex marriage.


“It’s very difficult to know why a particular appointment is made of a certain bishop to a certain diocese by the Vatican,” said Vincent Pizzuto, an associate professor of religious studies at the University of San Francisco, a Jesuit school. “But in this instance, it’s very difficult not to see this as a signaling of an attempt to rein in the diocese, particularly on hot-button issues like homosexuality and same-gender marriage.”


Supporters of Proposition 8 said they were heartened by the selection of Bishop Cordileone.


“It’s great for the church, and it’s great for San Francisco that he’ll be archbishop,” said Brian Brown, the president of the National Organization for Marriage, one of the many groups that campaigned for Proposition 8. “He’s a real leader on this issue.”


In 2007, Bishop Cordileone, who was auxiliary bishop in San Diego at the time, led an effort to put what would become Proposition 8 on the ballot, Mr. Brown said.


“I don’t know whether it would have gotten on the ballot in the first place,” he said. “So he was very indispensable.”


As the chairman of the defense of marriage subcommittee, Bishop Cordileone has written that marriage should be limited to the union between a man and a woman because “marriage has been and should remain a child-centered institution.” Bishop Cordileone has described the push for same-sex marriage as the latest evidence of the erosion of the institution of marriage in American society that began with the availability of contraceptives in the 1960s.