Pope Benedict said on Tuesday he was "deeply ashamed" over sexual abuse of children by priests and vowed to do everything possible to stop paedophiles entering the priesthood in future.
"We will absolutely exclude paedophiles from the sacred ministry," he told reporters accompanying him on his first trip as pope to the United States.
"We are deeply ashamed and will do whatever is possible so that this does not happen in the future," he said on board the plane to Washington.
The U.S. trip is the first by a pontiff since a wave of sex abuse scandals began in 2002, provoking lawsuits that have forced dioceses to pay more than $2 billion in settlements.
Benedict said the Church will do everything possible in screening candidates for the priesthood "so that only really sound persons can be admitted".
"It is more important to have good priests than to have many priests," said the pontiff, who will be greeted upon arrival at Andrews Air Force Base by U.S. President George W. Bush.
The pope is expected to discuss sexual abuse again during the six-day trip to the United States, during which he also will pray at Ground Zero in New York and address the United Nations.
Flagging the issue ahead of arrival, he said abuse had caused "great suffering" to the Church in the United States.
"If I read the histories of these victims, it's difficult for me to understand how it was possible that priests betrayed in this way their mission to give healing, to give the love of God to these children," he said.
A poll released this month by the Pew Forum on Religion & Public Life showed the German-born pope was viewed favourably by most Americans, but was not as popular as his predecessor John Paul II.
The pope, who will also mark the third anniversary of his election during the trip, has said he hopes the visit will lead to a spiritual renewal in America.
He addresses the United Nations on Friday and has said he aims to draw attention to the need for greater peace and justice around the world.
In New York, Benedict will also make a brief stop at a synagogue to wish the city's Jewish community a happy Passover.
He ends the trip on Sunday after visiting Ground Zero, the site of the World Trade Center towers destroyed in the Sept. 11, 2001 attacks on the United States. He will also say Mass at Yankee Stadium.
