Aug 14 (Reuters) - U.S. Republican presidential candidate John McCain and his Democratic rival Barack Obama will target faith voters on Saturday when they appear at a nationally televised faith forum moderated by California-based evangelical mega preacher Rick Warren.

Faith often plays a big role in U.S. politics, a point driven home by the fact that this will be the only event the candidates will share before their party conventions.

Following are some of the "faith factors" that each would bring to the contest and possibly Saturday's conversation.

ARIZONA SEN. JOHN MCCAIN

- Raised in the mainline Episcopal faith but for more than 15 years has attended a church in Phoenix affiliated with the Southern Baptist Convention (SBC), America's largest evangelical denomination and one of its most conservative.

- Widely seen as not being comfortable talking about his personal faith though he has spoken movingly about how it helped him through his ordeal when he was a prisoner-of-war during the Vietnam conflict.

- Support for stem cell research, failure to support a federal constitutional ban on gay marriage and past criticism of "Religious Right" leaders have made him suspect in the eyes of many conservative evangelical Christians who comprise a key part of the Republican base.

- About one in four U.S. adults count themselves as evangelical and the movement has been broadening its agenda beyond culture issues such as abortion to activism in areas such as poverty and climate change.

- This can work to McCain's favor among more centrist evangelicals who admire his consistent opposition to abortion rights combined with his condemnation of the use of torture by U.S. forces and more compromising tone on many issues.

- His recent campaign focus on increased U.S. drilling may disappoint evangelicals committed to a green agenda who were hoping he would take stronger action on climate change.

ILLINOIS SEN. BARACK OBAMA

- An adult convert to the United Church of Christ, a mainline Protestant denomination with about 1.2 million members nationwide. Obama was drawn to the church by his work in the 1980s with a faith-based organizing group in Chicago.

- Father came from a Muslim background in Kenya but Obama has said he was not religious. But this fact and his exotic sounding name to the American ear have given rise to erroneous rumors that the Illinois senator is a Muslim.

- One drawback on the faith front remains the fiery anti-American sermons made by his former pastor Jeremiah Wright which have angered many voters.

But Obama decisively distanced himself from Wright after the preacher continued to publicly make his more controversial statements such as the allegation that the U.S. government may have planted AIDS in the in the black community.

Obama also left Trinity United Church of Christ in Chicago -- a wrenching decision as it was the church in which he and his wife were married and where their children were baptized.

- Obama's own widely reported comments about rural white working class voters clinging to their "guns and religion" have also alienated some potential voters of faith.

- Obama is comfortable talking about his personal faith and has an outreach program pointedly targeting religious voters.

- Supports abortion rights and the granting of civil unions for gay couples. These positions go down well among liberal people of faith as well as many secular voters.

(Sources: Reuters, Pew Forum on Religion & Public Life, candidates' websites)

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