While some critics say the statistics are greatly exaggerated (one evangelical magazine for youth ministers dubbed it “the 4 percent panic attack”), there is widespread consensus among evangelical leaders that they risk losing their teenagers.

“I’m looking at the data,” said Ron Luce, who organized the meetings and founded Teen Mania, a 20-year-old youth ministry, “and we’ve become post-Christian America, like post-Christian Europe. We’ve been working as hard as we know how to work -- everyone in youth ministry is working hard -- but we’re losing.”

The board of the National Association of Evangelicals, an umbrella group representing 60 denominations and dozens of ministries, passed a resolution this year deploring “the epidemic of young people leaving the evangelical church.”

Among the leaders speaking at the meetings are Ted Haggard, president of the evangelical association; the Rev. Jerry Falwell; and nationally known preachers like Jack Hayford and Tommy Barnett.

Genuine alarm can be heard from Christian teenagers and youth pastors, who say they cannot compete against a pervasive culture of cynicism about religion, and the casual “hooking up” approach to sex so pervasive on MTV, on Web sites for teenagers and in hip-hop, rap and rock music. Divorced parents and dysfunctional families also lead some teenagers to avoid church entirely or to drift away.

Over and over in interviews, evangelical teenagers said they felt like a tiny, beleaguered minority in their schools and neighborhoods. They said they often felt alone in their struggles to live by their “Biblical values” by avoiding casual sex, risqué music and videos, Internet pornography, alcohol and drugs.

When Eric Soto, 18, transferred from a small charter school to a large public high school in Chicago, he said he was disappointed to find that an extracurricular Bible study attracted only five to eight students. “When we brought food, we thought we could get a better turnout,” he said. They got 12.

Chelsea Dunford, a 17-year old from Canton, Conn., said, “At school I don’t have a lot of friends who are Christians.”

Ms. Dunford spoke late last month as she and her small church youth group were about to join more than 3,400 teenagers in a sports arena at the University of Massachusetts in Amherst for a Christian youth extravaganza and rock concert called Acquire the Fire.

“A lot of my friends are self-proclaimed agnostics or atheists,” said Ms. Dunford, who wears a bracelet with a heart-shaped charm engraved with “tlw,” for “true love waits,” to remind herself of her pledge not to have premarital sex.

She said her friends were more prone to use profanity and party than she was, and added: “It’s scary sometimes. You get made fun of.”

To break the isolation and bolster the teenagers’ commitment to a conservative lifestyle, Mr. Luce has been organizing these stadium extravaganzas for 15 years. The event in Amherst was the first of 40 that Teen Mania is putting on between now and May, on a breakneck schedule that resembles a road trip for a major touring band. The “roadies” are 700 teenagers who have interned for a year at Teen Mania’s “Honor Academy” in Garden Valley, Tex.

More than two million teenagers have attended in the last 15 years, said Mr. Luce, a 45-year-old, mop-headed father of three with a master’s degree from the Graduate School of Business Administration at Harvard and the star power of an aging rock guitarist.

“That’s more than Paul McCartney has pulled in,” Mr. Luce asserted, before bounding onstage for the opening pyrotechnics and a prayer.

For the next two days, the teenagers in the arena pogoed to Christian bands, pledged to lead their friends to Christ and sang an anthem with the chorus, “We won’t be silent.” Hundreds streamed down the aisles for the altar call and knelt in front of the stage, some weeping openly as they prayed to give their lives to God.

The next morning, Mr. Luce led the crowd in an exercise in which they wrote on scraps of paper all the negative cultural influences, brand names, products and television shows that they planned to excise from their lives. Again they streamed down the aisles, this time to throw away the “cultural garbage.”

Trash cans filled with folded pieces of paper on which the teenagers had scribbled things like Ryan Seacrest, Louis Vuitton, “Gilmore Girls,” “Days of Our Lives,” Iron Maiden, Harry Potter, “need for a boyfriend” and “my perfect teeth obsession.” One had written in tiny letters: “fornication.”

Some teenagers threw away cigarette lighters, brand-name sweatshirts, Mardi Gras beads and CD’s — one titled “I’m a Hustla.”

“Lord Jesus,” Mr. Luce prayed into the microphone as the teenagers dropped their notes into the trash, “I strip off the identity of the world, and this morning I clothe myself with Christ, with his lifestyle. That’s what I want to be known for.”

Evangelical adults, like believers of every faith, fret about losing the next generation, said the Rev. David W. Key, director of Baptist Studies at the Candler School of Theology of Emory University, in Atlanta.

“The uniqueness of the evangelical situation is the fact that during the 80’s and 90’s you had the Reagan revolution that was growing the evangelical churches,” Mr. Key said.

Today, he said, the culture trivializes religion and normalizes secularism and liberal sexual mores.

The phenomenon may not be that young evangelicals are abandoning their faith, but that they are abandoning the institutional church, said Lauren Sandler, author of “Righteous: Dispatches from the Evangelical Youth Movement” (Viking, 2006). Ms. Sandler, who calls herself a secular liberal, said she found the movement frighteningly robust.

“This generation is not about church,” said Ms. Sandler, an editor at Salon.com. “They always say, ‘We take our faith outside the four walls.’ For a lot of young evangelicals, church is a rock festival, or a skate park or hanging out in someone’s basement.”

Contradicting the sense of isolation expressed by some evangelical teenagers, Ms. Sandler said, “I met plenty of kids who told me over and over that if you’re not Christian in your high school, you’re not cool -- kids with Mohawks, with indie rock bands who feel peer pressure to be Christian.”

The reality is, when it comes to organizing youth, evangelical Christians are the envy of Roman Catholics, mainline Protestants and Jews, said Christian Smith, a professor of sociology at the University of Notre Dame, who specializes in the study of American evangelicals and surveyed teens for his book “Soul Searching: the Religious and Spiritual lives of American Teenagers” (Oxford, 2005).

Mr. Smith said he was skeptical about the 4 percent statistic. He said the figure was from a footnote in a book and was inconsistent with research he had conducted and reviewed, which has found that evangelical teenagers are more likely to remain involved with their faith than are mainline Protestants, Catholics, Jews and teenagers of almost every other religion.

“A lot of the goals I’m very supportive of,” Mr. Smith said of the new evangelical youth campaign, “but it just kills me that it’s framed in such apocalyptic terms that couldn’t possibly hold up under half a second of scrutiny. It’s just self-defeating.”

The 4 percent is cited in the book “The Bridger Generation” by Thom S. Rainer, a Southern Baptist and a former professor of ministry. Mr. Rainer said in an interview that it came from a poll he had commissioned, and that while he thought the methodology was reliable, the poll was 10 years old.

“I would have to, with integrity, say there has been no significant follow-up to see if the numbers are still valid,” Mr. Rainer said.

Mr. Luce seems weary of criticism that his message is overly alarmist. He said that a current poll by the well-known evangelical pollster George Barna found that 5 percent of teenagers were Bible-believing Christians. Some criticize Mr. Barna’s methodology, however, for defining “Bible-believing” so narrowly that it excludes most people who consider themselves Christians.

Mr. Luce responded: “If the 4 percent is true, or even the 5 percent, it’s an indictment of youth ministry. So certainly they’re going to want different data.”

Outside the arena in Amherst, the teenagers at Mr. Luce’s Acquire the Fire extravaganza mobbed the tables hawking T-shirts and CD’s stamped: “Branded by God.” Mr. Luce’s strategy is to replace MTV’s wares with those of an alternative Christian culture, so teenagers will link their identity to Christ and not to the latest flesh-baring pop star.

Apparently, the strategy can show results. In Chicago, Eric Soto said he returned from a stadium event in Detroit in the spring to find that other teenagers in the hallways were also wearing “Acquire the Fire” T-shirts.

“You were there? You’re a Christian?” he said the young people would say to one another. “The fire doesn’t die once you leave the stadium. But it’s a challenge to keep it burning.”