ABOARD THE PAPAL PLANE — Pope Benedict XVI said Tuesday he was "deeply ashamed" of the clergy sexual abuse scandal in the Roman Catholic Church and will work to make sure pedophiles don't become priests.

Benedict was answering questions submitted in advance by reporters aboard a special Alitalia airliner as he was flying from Rome to Washington to begin his first papal pilgrimage to the United States.

"It is a great suffering for the Church in the United States and for the church in general and for me personally that this could happen," Benedict said. "It is difficult for me to understand how it was possible that priests betray in this way their mission ... to these children."

"I am deeply ashamed and we will do what is possible so this cannot happen again in the future," the pope said.

Benedict pledged that pedophiles would not be priests in the Catholic Church.

"We will absolutely exclude pedophiles from the sacred ministry," Benedict said in English. "It is more important to have good priests than many priests. We will do everything possible to heal this wound."

Benedict's pilgrimage was the first trip by a pontiff to the United States since the scandal involving priests sexually abusing young people rocked U.S. dioceses. The church has paid out more than $2 billion in abuse costs since 1950, with hundreds of millions in settlements just since 2002. Six U.S. dioceses have declared bankruptcy in recent years because of the financial toll of the scandal.

Pedophilia is "absolutely incompatible" with the priesthood," Benedict said.

Vatican officials selected four questions to be read by the journalists to the pontiff aboard the plane.

Benedict described his pilgrimage as a journey to meet a "great people and a great church." He spoke about the American model of religious values within a system of separation of church and state.

From a presidential welcome, to two Masses at baseball stadiums, to a stop for prayer at ground zero in New York, Benedict will get a heavy dose of the American experience.

President Bush planned to make the unusual gesture of greeting him at Andrews Air Force Base — the first time the president has greeted a foreign leader there.

The pope said he will discuss immigration with Bush, including the difficulties of families who are separated by immigration.

While the pope and Bush differ on such major issues on the Iraq war, capital punishment and the U.S. embargo against Cuba, they do find common ground in opposing abortion, gay marriage and embryonic stem cell research.

White House press secretary Dana Perino, asked about the pope's comments about the clergy sex abuse scandal, said she wouldn't rule out that the topic would come up in conversation between the pope and the president.

But she added that "I don't think it's necessarily on the president's top priorities" for his agenda in talking with the pope.

Perino said the two leaders would likely discuss human rights, religious tolerance and the fight against violent extremism.

As for the war in Iraq, Perino said, "Obviously, there were differences years back." She downplayed those, emphasizing instead a strong bond between Bush and the pope.

Peter Isely, a board member of the Survivors Network of those Abused by Priests, said the pope should go further and establish child protection policies for the worldwide church. He said penalties should be established for church leaders who fail to discipline predatory priests.

"It's easy and tempting to continually focus on the pedophile priests themselves," Isely said. "It's harder but crucial to focus on the broader problem — complicity in the rest of the church hierarchy."

Although a few bishops accused of molestation have stepped down, no bishop has been disciplined for failing to keep abusive clergy away from children. Cardinal Bernard Law resigned as archbishop of Boston in 2002 after church files were made public showing he and other church leaders had allowed accused clergy to continue in public ministry.

Benedict will give a speech at the United Nations during the second, New York leg of his six-day trip.

A crowd of up to 12,000, larger than the gathering for Queen Elizabeth II, is expected at the White House Wednesday to greet Benedict on his 81st birthday. Aides say he is in good health.

After making little headway in his efforts to rekindle the faith in his native Europe, the German-born Benedict will be visiting a country where many of the 65 million Catholics are eager to hear what he says.

A poll released Sunday by the Center for Applied Research in the Apostolate at Georgetown University found eight in 10 Catholics are somewhat or very satisfied with his leadership.

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Benedict is expected to stress the importance of moral values and take on what he sees are the dangers of moral relativism — that is, that there are no absolute rights and wrongs.

Also, while in New York, Benedict will visit the Park East synagogue, part of his efforts for close relations with Jews. Like his predecessor John Paul II, he has referred to Jews as "our older brothers in faith."

He also will celebrate Mass at Nationals Park in Washington and Yankee Stadium in New York, his last major event of the trip.