NEW ORLEANS — When Pope John Paul II arrives in the United States on Tuesday for a two-day visit to St. Louis, his first major speech in that city will be at a rally of Roman Catholic youth, a group the pope regards as vital to the church’s future.p. When he first visited this country as pontiff 20 years ago, John Paul was a relatively vigorous 59, and kept up a grueling schedule as he swept through cities in the Northeast and Midwest. He returns as a historic figure, a prophet of the postcommunist world and one of the longest-reigning pontiffs in history, but also far frailer physically.p. The church he will encounter here has been quieter politically than it was on his first visit and even in the 1980s, when the American bishops produced influential pastoral letters on war and peace and the nation’s economy. Controversies among lay people these days have tended to show up mainly in local parishes, as in Rochester, N.Y., last September when some Catholics objected to the removal of an outspokenly liberal priest as their pastor.p. But quietly, under the surface, the church is undergoing important shifts that will affect its future here well into the 21st century. Sociologists are finding that many young people are increasingly individualistic in their religious views and often divided from their elders on matters of sexuality.p. “That’s going to be the next Catholic constituency,” said Dean Hoge, a professor of sociology at the Catholic University of America, who is embarked with other academics on a major study of young Catholic adults. The study has found evidence of sharp generational polarization on issues like premarital sex and the leadership possibilities for women in church and society.p. At the same time, the church is becoming more ethnically diverse as a result of immigration from Asia and Latin America by Catholics who bring their own traditions and, in some cases, attitudes about church issues different from those of many of the American-born faithful.p. “We’re facing the many different kinds of people in our community that can’t be categorized as just liberals and conservatives,” said the Rev. Thomas Reese, editor of America, a Jesuit magazine. “We have to preach the Gospel to them and figure out how to make them one church.”p. Since 1979, the American Catholic population has grown through natural increase and immigration by more than a quarter, to 61.6 million people. The United States is now the world’s third-largest Catholic nation, behind Brazil and Mexico.p. Yet at the same time, the number of its priests has declined, the result of a plunge in seminary enrollments that began 30 years ago and has not been reversed.p. The changes can be readily sensed here in the Archdiocese of New Orleans, which once encompassed a territory so extensive it included St. Louis.p. Shortly before Mass at Ignatius Chapel at Loyola University, a Jesuit-run school in the city’s Uptown neighborhood, 10 undergraduates circle their chairs and lean in to speak avidly about what being Roman Catholic means to them. One sophomore calls the church her “centering point,” while a freshman says it is her “foundation.”p. But on some hot-button issues, where church teachings meet social controversies, the young Catholics disagree.p. Six declare premarital sex to be always wrong, and six say homosexual activity is wrong, too, positions in keeping with church teaching. Asked whether women should be allowed to be priests, a subject the Vatican has ruled off limits, the majority goes the other way, six raising their hands to say yes, while the four others quietly look on.p. New Orleans also reflects the church’s new ethnic diversity. While the city has long been home to a large African-American Catholic population, in recent years it has also been absorbing many immigrants from the Caribbean, Central America and Southeast Asia.p. In a former marshland remade as a suburban neighborhood sits the Mary, Queen of Vietnam parish, founded in 1983. During a midmorning Sunday Mass, the white-walled sanctuary was packed with worshipers, its pews, built to seat 1,000, so full that ushers had to search for spots for latecomers. “It’s typically this crowded,” said Anh Cao, 31, a law student at Loyola.p. Among younger parish members, social issues seem to elicit a generally conservative response, as when the question of whether women should be ordained is raised with members of a youth choir.p. “I have never thought of that,” said Kim Phan, 24, a graduate student at the University of New Orleans. “I’ve never imagined a woman could be a priest.”p. Hieu Hoang, 22, a junior at Louisiana State University who is a member of a parish women’s group, the Daughters of Mary, offered a similar response.p. Cao said Vietnamese Catholics strongly oppose abortion, in keeping with church teaching. Such attitudes reflect the continuity of traditional Vietnamese Catholic values, said Joseph Trung, 32, a choir director and composer. “It comes from the family, it comes from the community,” he said.p. But among American-born Catholics, sociologists are finding strong generational divisions on a variety of social issues.p. A recent article in America magazine by Hoge illustrated the trend with graphs showing findings from his study of younger Catholics that showed, among other things, that fewer than half of Catholics under 30 believed homosexual activity was always or almost always wrong — in contrast with a majority of those over 30 (and about three-quarters of those over 50) who thought it wrong.p. One of Hoge’s associates in that study, William Dinges, a Catholic University associate professor of religion, said the study has found that 90 percent of young people confirmed in the church retain their Catholic identity, a far higher proportion than found in a similar study of young adult Presbyterians.p. But, Dinges said, many of the young Catholics in the study indicated that they regarded the church not as the bearer of absolute religious truth, but as a denominational “option,” one form of Christianity among many.p. R. Scott Appleby, director of the Cushwa Center for the Study of American Catholicism at the University of Notre Dame, said that within such findings lie evidence of a loss of an “embedded” Catholic worldview among the faithful. “I suppose what’s been called radical individualism in American society is the biggest challenge to Catholic identity and to the Catholic church,” he said.p. But on a more positive note for the church, Dinges said the research also indicates that younger Catholics see the church’s sacramental life and a commitment to ideals of social justice as vital to their religious identity.p. A symbolic element of the pope’s visit will be his flight across the U.S.-Mexican border on a trip on which he will likely emphasize common concerns among North and Latin American Catholics.p. Reese said the trip will provide the pope his first opportunity to respond to Synod of America, a 1997 gathering in Rome of 200 bishops from the Western Hemisphere. Concerns voiced at that meeting included poverty, the debt burden among developing nations, the loss of Latin American Catholics to Pentecostal churches, and issues related to immigration.p. “The question of new immigrants in the United States, which is a north-south issue,” Reese said, is one the pope will likely focus on.p. An estimated 2 million Hispanic immigrants entered the country in the early and mid-1990s, most of them Catholics. But within the church, other ethnic groups have grown, too, among them the Vietnamese.p. Monsignor Dominic Luong, pastor of Mary, Queen of Vietnam, said the parish had about 3,000 members when it began in 1983. But now, he said, there are 17,000 Vietnamese Catholics in the New Orleans archdiocese.p. He said the parish had recently contributed $7,000 to a collection for Central American victims of Hurricane Mitch, and that the local Vietnamese population had produced 31 priests and had 47 young men and women studying to become priests and nuns.p. That would be a bright spot in a serious problem for the church. A growing priest shortage has meant that an ever-larger number of tasks, from administering parishes to working with immigrants to teaching youth in Catholic schools, is falling to lay people, said Appleby. “That’s a structural challenge that the church needs to take more seriously,” he said.