Pope Benedict XVI arrived at Andrews Air Force Base near Washington, D.C., for his first official visit to the United States on Tuesday, and was greeted upon landing by President George W. Bush and first lady Laura Bush.

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After greeting U.S. church officials and dignitaries, a motorcade conveyed the popeand president's entourage to the Vatican's embassy.

Earlier, as he flew aboard a special transatlantic Alitalia flight, Benedict told reporters traveling with him from Rome that he is "deeply ashamed" of the clergy sexual abuse scandal that stained the Catholic Church.

And while the pontiff pledged to work to make sure that such abuse won't happen again and that pedophiles don't become priests, the White House said other matters will be on the official agenda when the pope meets formally with Bush.

White House press secretary Dana Perino said the abuse scandal may come up in conversations between the pope and the president, though it's not a "top" priority. She said the two leaders will likely discuss immigration, human rights, religious tolerance and the fight against violent extremism in the world.

Perino said the two also share similar views on abortion and tyranny.

Bush plans to make the unusual gesture of greeting the pope upon his arrival at Andrews Air Force Base Tuesday. It's the first time the president has greeted a foreign leader there.

The pope's six-day visit to Washington and New York is scheduled to be filled with high-profile events.

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.

Benedict will give a speech at the United Nations during the second, New York leg of his six-day trip. He also plans to visit the site of the Sept. 11, 2001, terrorist attacks, and officiate at a Mass at Yankee Stadium.

Those who have met Pope Benedict said the nation should expect a man who knows and admires much about the United States, but who also sees a culture in need of moral guidance.

Former Boston Mayor Ray Flynn, who served as U.S. ambassador to the Vatican from 1993 to 1997, said he was amazed by Benedict's "curiosity and awareness" about what was happening in the United States, both among its 65 million Catholics and in the population at large.

Flynn is among those hosting a birthday party for Benedict on Wednesday night in Washington, although it's not clear if Benedict will attend.