In the marketplace of American faith, Catholicism is the big loser. Catholics have lost more members to other faiths, or to no faith at all, than any other U.S. religion, according to the new survey released by the Pew Forum on Religion & Public Life. The survey, based on interviews with 35,000 U.S. adults, found that 31 percent of Americans were raised Catholic, but only 24 percent still identify as Catholic. Perhaps more worrisome for church leaders, while 2.6 percent of Americans converted to Catholicism, four times as many -- 10.1 percent -- of cradle Catholics have left for another faith or no faith at all. Roughly 10 percent of all Americans are former Catholics, the study reported. Still, despite the loss, Catholics remain steady at one in four of all Americans, the nation's single largest religious group. That stability is fueled in part, researchers said, by waves of Hispanic immigrants, much like generations of Irish and Italians built up the church in earlier generations. "It may well be that a factor in the Catholic numbers are the repeated waves of immigration," said John Green, senior fellow at the Pew Forum. The study found that almost half of all immigrants coming to U.S. shores are Catholics, most of them from Latin American countries. Latinos now represent 45 percent of Catholics aged 18 to 29, but only 20 percent of Catholics in their 50s. Much of Catholicism's loss can be chalked up to previous generations of immigrants who assimilated into American culture and as a result became less faithful to their ethnic identities and religions, Green said. "That kind of assimilation is typical for any ethnic group," said Mary Gautier, senior research associate at the Center for Applied Research in the Apostolate at Georgetown University. "And it affects all religions -- not just Catholicism." Gautier listed interfaith marriages, a dwindling supply of priests and insufficient church facilities as challenges to keeping people in the pews. Others, such as the Rev. Allan Figueroa Deck of the U.S. Conference of Catholic Bishops, cited a lack of manpower. "The Church is falling behind," said Deck, executive director of cultural diversity for the bishops. "We don't have enough foot soldiers." Deck downplayed the idea that church teachings are out of step with the times -- the church's stand on birth control has alienated many Catholics, observers say -- and said there simply aren't enough teachers to communicate the faith. "It's our mission to evangelize," he said, noting that part of that job involves changing hearts and minds, "and we are failing that." The Catholic Church also struggles to reach out specifically to the needs of minority communities, such as blacks, Asians and Hispanics, said Deck, who has spent his career in the Hispanic ministry. And the assimilation of immigrants into the church and also American culture is a tricky balance, he said. "We have to be very careful," Deck said. "Our role is to promote the Gospel, not any particular culture -- not even American culture."