US Republican presidential candidate John McCain has a "Religious Right" problem. His likely Democratic rival, Barack Obama, has a Rev Wright problem.

In a country where high levels of belief and church attendance often translate into a major role for religion in politics, analysts say faith may well be a poisoned chalice for the likely contenders in the November White House race.

The faith problem for Obama, who would be the first black president and is within striking distance of the Democratic nomination, stems from voter anger over anti-American sermons by his former pastor the Rev Jeremiah Wright.

Wright has said the September 11 attacks were retribution for US foreign policy and the US Government had a hand in spreading Aids to harm blacks.

Obama has severed ties with Wright but opinion polls persistently show the relationship matters to some voters.

McCain's trouble lies with the Republican Party's conservative evangelical base, the so-called Religious Right, which rallied behind President George W Bush but has been less than enthusiastic about McCain because of his past support for stem-cell research and his failure to back a federal ban on gay marriage.

"The religious right challenge to McCain is far more significant and problematic for his candidacy than the Rev Wright problem for Obama. The reason is because religiously committed Christians are fundamental to a Republican winning the White House," said Michael Lindsay, a political sociologist at Rice University in Houston and a noted expert on faith and politics.

"That is not the case for Democratic candidates, in fact quite the opposite. The so-called secularist wing of American politics is part of the core of Democratic support and especially Obama support," he said.

But that does not mean Obama can exorcise the ghost of Wright, and Lindsay said it could haunt him in swing states - those states that often switch from one party to the other and where the margin of victory in presidential elections is often narrow.

"I think the Wright controversy will continue to plague Obama's candidacy in swing states where religious voters can make a difference like Missouri, Ohio and Pennsylvania."

Polls of voters taken after Tuesday's Kentucky Democratic primary, which Hillary Clinton won easily in what many see as one of her last stands, showed that more than 50 per cent of those who voted thought Obama shared Wright's views.

This highlights the scope of the Wright problem for Obama among Clinton's white, working-class and often church-going supporters in swing states - voters who could be up for grabs in an Obama-McCain showdown.

CAN MCCAIN REAP THE WRIGHT STUFF?

But can McCain reap what Wright has sown?

Many of the conservative evangelicals whom McCain needs to woo are staunchly patriotic and are enraged by Wright's inflammatory statements. That could help divert attention from McCain's perceived drawbacks.

"I don't think the McCain campaign will dwell on it but the rest of the Republican machinery will try and keep the Rev Wright controversy at a low boil," said Cal Jillson, a political analyst at Southern Methodist University in Dallas.

McCain also has positions and qualities that many conservative Christians find appealing, such as his consistent opposition to abortion and his status as a military hero and former prisoner of war in Vietnam.

Those qualities won him an endorsement from controversial Texas megapastor John Hagee. McCain rejected the preacher's backing last week after a sermon from the 1990s came to light in which Hagee said Hitler and the Holocaust were foretold in the Bible and thus sanctioned by God.

But Obama's ease at talking about his personal faith - a trait he shares with Bush - stands in stark contrast to McCain's obvious discomfort with the subject.

McCain attends a church affiliated with America's largest evangelical denomination, the Southern Baptist Convention, but he was raised in the more reserved embrace of the Episcopal faith. Obama is an adult convert to the United Church of Christ and the convert's passion gels easily with his speaking style.

"The political problem Obama faces (because of Wright) can be solved by personalising the issue of faith," Jillson said.

Obama's campaign also has a faith outreach programme aimed at religious voters, which helps dispel false rumours that he is a Muslim.

Clyde Wilcox of Georgetown University in Washington said he saw the Wright issue fading but it has still hurt "because there are people who are looking for a reason to doubt him (Obama) ... But Obama can survive this, he talks so very well about religion and has forcibly distanced himself (from Wright)".