McDonough said the topics discussed included interfaith dialogue, a shared desire for Middle East peace, the president's effort to reach out to Muslims, a mutual desire to fight militarism and extremism and a shared interest in overhauling immigration rules and practices.

Some Catholic activists and American bishops have been outspoken in their criticism of Obama, though polls have shown he received a majority of Catholic votes.

"There's no question what the pope made his priority," said John Allen, a Vatican expert for the National Catholic Reporter. "When other leaders visited him this week they were only given his new encyclical."

Obama is very popular in Italy, and hundreds of people lining the broad avenue leading to St. Peter's Square cheered his limousine as it went by. Obama waved.

His election presented a challenge for the Vatican after eight years of common ground with President George W. Bush in opposing abortion, an issue that drew them together despite Vatican opposition to the war in Iraq.

But the Vatican has been openly interested in Obama's views and scheduled an unusual afternoon meeting to accommodate him at the end of his Italian stay for a G-8 summit in the earthquake-stricken city of L'Aquila.

L'Osservatore Romano, the Vatican's daily newspaper, gave Obama a positive review after his first 100 days in office. In a front-page editorial, it said that even on ethical questions Obama hadn't confirmed the "radical" direction he discussed during the campaign.

Tensions grew in the spring when Obama was invited to receive an honorary degree at the leading U.S. Catholic university, Notre Dame. Dozens of U.S. bishops denounced the university, and the local bishop pointedly declined to attend the ceremony.

Former St. Louis Archbishop Raymond Burke, who now heads a Vatican tribunal, accused Obama of pursuing anti-life and antifamily agendas. He called it a "scandal" that Notre Dame had invited him to speak.

As a child in Indonesia, Obama's Muslim father enrolled him in Catholic school for a few years. Obama is a Protestant.

McDonough, the Obama national security aide, spoke to reporters about the influence of Catholic social teaching on Obama, saying the president "expresses many things that many Catholics recognize as fundamental to our teaching."

In an interview with Catholic journalists before meeting the pope, Obama said he would tell Benedict of his concern that the global financial crisis not be "borne disproportionally by the most poor and vulnerable countries."

Just this week, Benedict issued a major document calling for a new world financial order guided by ethics and a search for the common good, denouncing a profit-at-all-cost mentality blamed for the global financial meltdown.

As Obama has pledged to step up efforts for Middle East peace through a two-state solution, Benedict made a similar appeal during a trip in May to Jordan, Israel and the Palestinian territories. He issued the Vatican's strongest call yet for a Palestinian state.

Obama's wife, Michelle, joined him at the end of the meeting with Benedict, and gifts were exchanged. Daughters Malia and Sasha, who accompanied their parents on the trip, also met the pope.

Obama gave Benedict a letter from Sen. Edward Kennedy, who was diagnosed a year ago with brain cancer. McDonough said Obama asked the pope to pray for Kennedy, a member of one of the United States' most prominent Roman Catholic families and a politically ally of the president.