WASHINGTON - Pope Benedict XVI prayed with tearful victims of clergy sex abuse in a chapel Thursday, an extraordinary gesture from a pontiff who has made atoning for the great shame of the U.S. church the cornerstone of his first papal trip to America.

But the real drama happened privately, in the chapel of the papal embassy between events.

The Rev. Federico Lombardi, a papal spokesman, said that Benedict and Boston Cardinal Sean O'Malley met with a group of five or six abuse victims for about 25 minutes, offering them encouragement and hope. The group from O'Malley's archdiocese were all adults, men and women, who had been molested when they were minors. Each spoke privately with the pope and the whole group prayed together.

One of the victims, Bernie McDaid, told The Associated Press, that he shook the pope's hand, told him he was an altar boy and had been abused by a priest in the sacristy of his parish. The abuse, he told Benedict, was not only sexual but spiritual.

"I said, 'Holy Father, you need to know you have a cancer in your flock and I hope you will do something for this problem, you have to fix this,'" McDaid said. "He looked down at the floor and back at me, like, 'I know what you mean.' He took it in emotionally. We looked eye to eye."

McDaid said the importance of the moment has not sunk in, but that he and others had waited a long time for it, and that "if everyone wants change, then change will occur."

Olan Horne, another Boston-area victim who prayed and talked with Benedict, told the AP, "there was an ... unscripted, unfiltered opportunity face-to-face. I believe we turned the pope's head a little in the right direction."

Both men have worked with church officials in the aftermath of the crisis, including meeting with a new office established by U.S. bishops in response to the scandal.

O'Malley had invited Benedict to Boston as part of his U.S. journey, and when that didn't work out, the cardinal kept in touch with the papal nuncio, Benedict's representative in the U.S., to see if it was possible to put him in touch with victims during the visit, said the Rev. John Connolly, a special assistant to O'Malley.

"The desire to do this was definitely from the Holy Father," Connolly said.

The pope ultimately asked O'Malley to invite a small group of victims who were "both open to meeting him and would derive a spiritual benefit," Connolly said.

Well over 4,000 priests have been accused of molesting minors in the U.S. since 1950. The church has paid out more than $2 billion, much of it in just the last six years, after the case of a serial molester in Boston gained national attention and inspired many victims to step forward. Six dioceses have been forced into bankruptcy because of abuse costs.

Expected to address the problem only once during his six-day trip ? at a Mass with priests in New York City on Saturday ? Benedict has instead returned to the issue repeatedly, beginning in a news conference on the flight from Rome to the U.S.

He has called the crisis a cause of "deep shame," pledged to keep pedophiles out of the priesthood and decried the "enormous pain" that communities have suffered from such "gravely immoral behavior" by priests.

On Wednesday, he told bishops the problem has sometimes been very "badly handled" and said it was their God-given duty to heal the wounds caused by abuse. He asked each parishioner at Mass on Thursday "to do what you can to foster healing and reconciliation, and to assist those who have been hurt."

But Thursday afternoon's session went a step further. Lombardi said it was believed to be the first-ever such session between a pope and abuse victims.

Gary Bergeron, an outspoken abuse survivor from Boston who was not in the meeting, failed in his attempt to meet with Pope John Paul II, Benedict's predecessor, when he spent a week at the Vatican a few years ago. He called the session "a long-sought-for step in the right direction."

Lombardi said that O'Malley presented the pope with a notebook listing the names of sexual abuse victims from the Boston Archdiocese. There were more than 1,000, he said.

The Survivors Network of those Abused by Priests called the meeting "a positive first step on a very long road." The group, which has been fiercely critical of the church, said it hopes the meeting will lead to reform in how church leaders respond to abuse claims.

The session came just hours after the pope celebrated the first public Mass of his U.S. pilgrimage.

More than 45,000 people filled Nationals Park on a clear spring day as the pope led the service from an altar erected in centerfield.

In his homily, Benedict called the United States a land of opportunity and hope but decried that the nation's promise has been left unfulfilled for some. He said he detected anger and alienation, increasing violence and a "growing forgetfulness of God."

"Americans have always been a people of hope," the pontiff said. "Your ancestors came to this country with the experience of finding new freedom and opportunity.

"To be sure, this promise was not experienced by all the inhabitants of this land; one thinks of the injustices endured by the native American peoples and by those brought here forcibly from Africa as slaves."

Later, the pope told leaders of America's Roman Catholic colleges and universities that academic freedom has "great value" for the schools, but it does not justify promoting positions that violate the Catholic faith.

Also Thursday, the pope met with Jewish and Muslim leaders, along with leaders of other faiths, and affirmed the church's commitment to interreligious dialogue.

At 5:45 a.m., more than four hours before the Mass, it was standing-room only on Washington subways. Vendors hawked Vatican flags and souvenir buttons, but there were few takers as people hurried toward the stadium.

The Catholic faithful were excited to see Benedict. At the end of the two-hour Mass, the pope blessed the cheering crowd, some of them waving Vatican flags. Worried-looking papal bodyguards stood close and cleared a way for him as he walked out, while many worshippers tried to shake his hand or touch his robes.

A number of lawmakers who support abortion rights attended the Mass, including House Speaker Nancy Pelosi and Sen. John Kerry, the former Democratic presidential candidate. During the 2004 campaign, several bishops questioned whether Kerry should receive Communion because of his stand on abortion. The Massachusetts Democrat who took Communion from a priest far from the papal altar.

For some, the experience of Mass with Benedict was overwhelming. It made Barbara Loh of Williamsburg, Va., tear up.

"I've been Catholic all my life," she said. "My dream has always been to see the pope."

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AP Religion Writers Eric Gorski and Rachel Zoll contributed to this report.