In Major Poll, U.S. Religious Identity Appears Very Slippery

But Oscar Mendez, who coordinates charismatic renewal for the Arlington Diocese, said he sees evidence of Catholics leaving, particularly for Protestant denominations. According to Pew, one in 10 Protestants was raised Catholic. Too many Catholics, Mendez said, fall back on the label but don't engage with the church and don't have a "mature" faith. Protestants, he said, have been better at creating conditions for people to "have an experience" with Jesus.

More than anything else in the poll, Pew highlighted the fluidity of identity, noting that every group is constantly gaining and losing members. Twenty-eight percent of Americans have left the group they were raised in, switching, for example, from Protestantism to Judaism or from the Orthodox faith to Catholicism. When people who have switched from one Protestant denomination to another are included, the number jumps to 44 percent.

America has always been very religiously vibrant, said Pew political scientist John Green, but today there are more options, more "things you can move from and to."

Fred Kurth, a retired aerospace engineer, was married at Fifth Avenue Presbyterian Church in Manhattan. He later became a Unitarian Universalist and led several congregations as he moved around the world with General Electric. After meeting his second wife in Morocco, he had to face a hard choice: convert to Islam or forgo marrying her.

"I was soul-searching. I had to answer, How far is it? If I'm a Unitarian, I believe there is a direct link between me and God, and no third party to go through, how different is that from Islam?"

Today Kurth, who took the name Ibrahim, prays every day at the mosque near his home in Fredericksburg and carries a prayer rug in his car.

The group that has grown the most is made up of those who are unaffiliated, including people who call themselves atheist and agnostic. Also included in this group are those who said they are "nothing in particular" -- some of whom went on to say religion is "very important" to them. Seven percent of survey respondents said they were raised as unaffiliated, less than half the percentage who call themselves unaffiliated today.

Anh Khochareun, a teacher's assistant from Manassas, was raised as a Buddhist in Vietnam, but she converted to Catholicism as a teenager after immigrating to this country. Now, she said, she and her husband don't identify with any denomination, and she is no longer sure that she believes in a God.

"We make our own faith," she said, "within what we can do for ourselves in our own lives right now."