Pope Benedict XVI, embarking on his first visit to the United States as pontiff, said Tuesday he is "deeply ashamed" of the sexual abuse scandal that has shaken the Roman Catholic Church in this country and pledged greater efforts by the church to bar pedophiles from the priesthood.

Speaking to reporters aboard his plane from Rome, the pope made his most extensive comments about the abuse crisis to date, saying the scandal that erupted in the United States in 2002 has caused "great suffering" for the church and for "me personally."

Hours later, the pope, who will turn 81 Wednesday, was welcomed upon his arrival at Andrews Air Force base outside Washington by President Bush, in what the White House said was an unprecedented show of deference by the president for a foreign leader.

The white-haired Benedict, waving and smiling broadly, was met at the foot of the Alitalia airliner's stairs by the president, first lady Laura Bush and their daughter Jenna.

There were no public statements made or planned; the pope and the president are scheduled to hold private discussions at the White House on Wednesday, after an official welcoming ceremony that may draw as many as 9,000 guests to the South Lawn.

Benedict's six-day visit to Washington and New York is the first by a pope to the U.S. since revelations of clergy sexual abuse were first made in Boston and later spread to dioceses across the country. The scandal, in which thousands of victims alleged they had been molested or raped by priests, has cost the church more than $2 billion in legal settlements to date, bankrupted five dioceses and shattered families and parishes across the country. Many of the victims were children at the time of the abuse.

"We are deeply ashamed," the pope said in his comments to reporters on the plane. "We will do what is possible so this cannot happen again in the future."

A spokesman for one victims group, the Survivors Network of Those Abused by Priests, said he hoped for more.

"Talk is cheap; action is better," David Clohessy, national director of the group, said in an interview. "He's been pope for three years and a top Vatican official for three decades. Expressions of remorse and promises of reform ... ring pretty hollow at this point."

No meeting with victims is scheduled at this point, although Vatican officials have hinted that one may occur, perhaps informally and in private.

Benedict also signaled Tuesday that he plans to raise the issue of immigration during his visit. He told reporters that he was especially concerned about what he called the grave problem of families separated by immigration policies and about border violence.

Another subject that may arise during his White House session is the Iraq war, which the pontiff has strongly opposed.