(AP) - In a moment weaving strands of politics, religion and emotion, Pope Francis and President Barack Obama met in the grandeur of the Oval Office to advance causes dear to them both.

Their meeting followed an elaborate welcome ceremony for Francis on the South Lawn of the White House that took place under sunny, blue skies in front of some 15,000 onlookers.

After the ceremony, Obama led Francis into the White House. They reappeared on a balcony and waved to the throngs huddled on the lawn and walked along the colonnade and past the famed Rose Garden on the way to the president's office.

Each leader addressed the contentious climate change issue in brief remarks to the crowd. It's one of several issues on which they agree and a likely topic of discussion in their meeting.

From the instant the white-robed and broad-grinned Francis landed in the U.S. on Tuesday, doffed his skullcap in the breeze and got into a modest, charcoal-gray Fiat, his visit electrified wonky Washington, which can be jaded about the comings and goings of world figures.

Washington was the first stop on the pope's six-day, three-city visit to the United States.

People of all faiths wanted to be a part of it, from the hundreds on hand for his arrival at Andrews Air Force Base to the clumps of spectators outside the diplomatic mission where the pope was staying.

"These moments matter," said May Lynne Duncan, who battled traffic from suburban Virginia to bring her two daughters to stand outside the nunciature.

For all of the oh-wow enthusiasm attending the visit, the pope and the president, with overlapping but far-from-identical agendas, had serious matters to attend to.

Even before he arrived for his first U.S. visit, Francis was fending off conservative criticism of his economic views. He told reporters on his flight from Cuba that some people may have an inaccurate impression that he is "a little bit more left-leaning."

"I am certain that I have never said anything beyond what is in the social doctrine of the church," he said.

As for conservatives who question whether he is truly Catholic, he added jokingly, "If I have to recite the Creed, I'm ready."

Obama was anxious to add oomph to his own efforts to combat climate change, fight income inequality and promote social justice, among other things, by finding common cause with the pope. The two differ sharply on other issues, such as abortion and same-sex marriage.

From Francis' vantage point, his next stop after the White House was perhaps more critical. The 78-year-old pontiff was meeting with America's 450-strong bishops' conference at the Cathedral of St. Matthew the Apostle.

Many U.S. bishops have struggled to come to terms with Francis' new social justice-minded direction of the church. Nearly all were appointed by Popes John Paul II and Benedict XVI. They prioritized drawing clearer boundaries for Catholic behavior and belief in the face of legalized abortion, advances in gay rights and the exodus of so many Westerners from organized religion.

The American church spends hundreds of millions of dollars each year through its social service agencies, and for years has sought an overhaul of the immigration system to reunite families, shelter refugees and give the poor the chance at a better life. But the U.S. Conference of Catholic Bishops has increasingly put its resources behind high-profile fights over abortion, contraception and gay marriage.

The first pope from the Americas also was acting Wednesday to canonize a Spanish friar who brought the Catholic faith to California.

Francis was to celebrate the Mass of canonization for Junipero Serra in Spanish. Several thousand of the 25,000 tickets to the event were set aside for Spanish-speaking people, many from California. The Basilica of the National Shrine of the Immaculate Conception erected a temporary sanctuary on the east portico for the Mass.

On Thursday, Francis planned to deliver the first papal address ever to Congress, speaking to Republican-majority legislators deeply at odds with Obama on issues such as gay rights, immigration, abortion and climate change. Those same issues are roiling the early months of the presidential campaign.

For all the focus on Francis' speeches, his less scripted moments in meeting with immigrants, prisoners and the homeless could prove more memorable.

He was expected to meet with poor immigrants and other clients of Catholic Charities in Washington and with prisoners in Pennsylvania. He also is known to veer off schedule for unscripted encounters.