NEW ORLEANS -- The church Pope John Paul II will encounter when he arrives in the United States on Tuesday for a two-day visit to St. Louis has been quieter politically than it was on his first visit as pontiff 20 years ago and even in the 1980s, when the American bishops produced influential pastoral letters on war and peace and the nation's economy.

But 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."That's going to be the next Catholic constituency," said Dean Hoge, a professor of sociology at the Catholic University of America, who has embarked with other academics on a major study of young Catholic adults. The study has found evidence of sharp generational polarization on issues such as premarital sex and the leadership possibilities for women in church and society.

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.

"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."

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.