* Obama and Pope Francis to meet for first time
* They converge on social issues, diverge on abortion and gay marriage
* Obama may invite Pope Francis to visit United States next year
Despite differences on moral issues, U.S. President Barack Obama will find in Pope Francis a welcome ally on issues of poverty and social justice when they meet for the first time at the Vatican on Thursday.
The president has sparred with the Catholic Church hierarchy in the United States over his support for abortion rights, gay marriage and the "contraception mandate" that requires employers to provide health insurance coverage for artificial birth control.
But the pope, while making clear that there will be no changes to Catholic doctrine on such issues, has used softer language than his predecessors.
In taking some of the heat out of the issue, he has tried to focus the Church instead on helping the world's disadvantaged, and signalled his dislike for the polarizing effects of "culture wars" among U.S. Catholics.
"Francis has made it clear that his emphasis is on poverty, immigration and other social issues," said Monsignor Robert Wister, theologian and professor of Church history at Seton Hall University in the United States.
Since his election a year ago, Pope Francis has several times criticized unbridled capitalism, the excesses laid bare by the global financial crisis, and the growing gap between the rich and poor, even in developed countries.
For his part, Obama has repeatedly praised the pope for his compassion and emphasis on helping the poor, and the meeting could help to give impetus to some of his initiatives back home, such as boosting the middle class and helping low-income Americans succeed.
The White House said Obama wanted to discuss "pressing global challenges such as lack of economic mobility and opportunity," adding that the pope's voice was "a crucial one as we look around the world at areas of conflict, religious persecution, and poverty".
Pope Francis' more open-minded attitude toward women and gays also resonates with Obama, who counted on both groups to help propel him to the presidency in 2008 and 2012.
"The President, I think like many people around the world, has been inspired by the first year that Pope Francis has had, by the way in which he has motivated people around the world, by his message of inclusion, of equality, which has deep meaning for people ... of the Catholic faith, but (also for) people of different faiths all over the world," said Ben Rhodes, White House deputy national security adviser.
Catholics were also an important constituency for Obama's re-election and they are a key group for Democrats in November's midterm elections.
When Obama met then-pope Benedict in 2009, the pope raised abortion, a sensitive issue for many U.S. Catholics as the Church considers abortion a grievous sin. Obama promised to do everything he could to reduce the number of abortions.
U.S. Church officials want Pope Francis to visit the United States for a meeting of Catholic families in Philadelphia in 2015, and Obama may extend an open invitation, a U.S. Church official said.
Obama, a Christian, has kept his religion a mostly private affair, rarely attending church in Washington, D.C., since his election in 2008. He receives daily "devotional messages" from an informal spiritual adviser, mostly based on Scripture.