Barely 51% of Americans are Protestants, and among 18- to 29-year-olds, just 43% identify with this branch of Christianity, according to the study by the Pew Forum on Religion & Public Life. Protestants have always held a majority status in the United States.
At the same time, more than four in 10 adults -- 44% -- have switched religious affiliations or abandoned ties to a specific religion, according to the survey, which provides one of the most detailed looks at U.S. religious affiliation. The Census Bureau stopped asking questions about religion in the late 1950s.
Steve Savage, 53, of San Diego said switching religions was common in his family. He grew up in a house with a Lutheran mother and a Roman Catholic father who attended an Episcopal church. His parents later switched to a charismatic congregation.
Although they started out as Presbyterians, Savage said he and his wife eventually joined a nondenominational church. "I fundamentally did not change what I believe, but I changed brands," Savage said.
Leo Poveda, 43, a Los Angeles native who was born into a Catholic family, said he became a nondenominational evangelical in 2004. Catholicism "never took a hold of me," he said. It was too formal and ritualistic with a "maze of people and titles."Since becoming an evangelical, Poveda says said he feels his faith has come alive: "This is God talking to me."
The Pew study also found that immigrants were twice as likely as native-born Americans to identify with the Roman Catholic Church, with one in three adult Catholics being Latino.
Father Guillermo Garcia, pastor at St. Gertrude's Catholic Church in Bell Gardens, said the large numbers of Catholic immigrants were stabilizing the church's membership. But, he said, "even if they come, there is a tendency to lose them in the second and third generation."
The Catholic Church needs to find more creative ways to reach out to the community, said Garcia, a professor of systematic theology at Mount St. Mary's College: "We are very much a liturgical assembly. We have some of the ancient structure. We don't use the resources of television, radio and the Internet as well as others."
The 148-page Pew study is the first report of the U.S. Religious Landscape Survey and is believed to be one of the most comprehensive snapshots of religious affiliation. The study was based on telephone interviews in English and Spanish with a representative sample of more than 35,000 adults in the contiguous United States. The interviews, which included 40 questions, were conducted from May 8 to Aug. 13, 2007. "The presumption of a Protestant framework for understanding the American character is now a thing of the past," said Richard J. Mouw president of Fuller Theological Seminary in Pasadena. "We are an increasingly pluralistic society, and we Protestants now have to think much about how we can contribute to the common good as simply just one more voice in the American choir," he said in an e-mail.
But Jerry D. Campbell, president of the Claremont School of Theology, a United Methodist seminary, questioned whether the United States ever was a Protestant nation.
"Early on, Europeans came to America at least in part so that they could enjoy religious freedom," he said in an e-mail.
"Thus they adopted the principle of the separation of church and state. So, technically, one would not say that this was ever a Protestant nation, rather it was a nation made up primarily of individuals who professed to be Protestants."
According to the study, 78.4% of Americans are Christians, about 5% belong to other faith traditions and 16.1% are unaffiliated with any religion.
Secular unaffiliated Americans account for 6.3% of the population; religious unaffiliated, 5.8%; atheists, 1.6%; and agnostics, 2.4%.
At 1.7% of the population, Jews make up the next-largest religious group. Buddhists are 0.7% of the population; Muslims 0.6%; and Hindus and New Age followers, both 0.4%.
The study noted that Protestantism is characterized by significant internal diversity and fragmentation, encompassing hundreds of denominations loosely grouped around three "fairly distinct" religious traditions -- evangelical Protestant churches (26.3%), mainline Protestants (18.1%) and historically black Protestant churches (6.9%).
Evangelicals make up the nation's single-largest religious tradition, followed by Catholics, who comprise nearly one-fourth of Americans.
But Catholics also lost more adherents, with one in three adults who were raised as Catholics no longer in the church, the study said. Roughly 10% of Americans are former Catholics. "These losses would have been even more pronounced were it not for the offsetting impact of immigration," the study said.