For Bush, the challenge lies in placating his Christian conservative base with strong religious language, while not alienating moderate swing voters.

Kerry on the other hand, must use the issue of faith to appeal to Catholics and conservative Democrats without turning off the more secular wing of the Democratic Party.

There is no clear consensus among experts on which candidate has the more difficult task ahead.

Many feel Kerry faces the bigger challenge because of the widespread belief that liberal voters on the far left are less religious and more easily disenchanted by the use of religion in a political campaign.

Yet, many Democrats, like Republicans, believe faith and values are closely linked when it comes to a presidential candidate.

'Fine line'

"That is precisely the fine line that [Kerry] has to walk," said Luis Lugo, director of the Pew Forum on Religion and Public Life, a research organisation in Washington.

"He cannot sound so religious that he turns off the section of the Democratic Party that is secular," he said.

Bush does not have to worry about appearing too religious to his conservative base, Lugo said.

"Bush does not have that challenge, because on his side there is not a large swath of seculars," he said.

With the exception of African Americans, polling data shows the majority of voters who attend church services at least once a week vote Republican.

Bush's challenge

Some experts, however, said the president has a more complex balancing act to perform.

His conservative base, of which evangelical Christians are a significant part, have already pulled Bush "further to the right than he wants to be", said Alan Wolfe, director of The Boisi Center for Religion and American Public Life at Boston College.

Bush is "the most openly devout
president in recent years"

"I actually think that Bush has the more difficult challenge here," Wolfe said.

The Bush administration's decision to propose a constitutional ban on gay marriage, he said, was a reluctant concession to the evangelical Christian community.

"Evangelicals are pretty demanding ... They're not all that satisfied it seems," he said.

Despite all the talk of secular liberalism, the Democratic Party is so firmly united in its effort to oust Bush from power, that Kerry might have more flexibility to reach out to religious swing voters.

"Using religion won't hurt Kerry on the left because there is such a desire on the left to get Bush out that he will have a lot of leeway," Wolfe said.

Men of faith

Both Bush and Kerry are men of faith, though the president has generally been more vocal about his beliefs as a born-again Christian than Kerry has as a Catholic.

"I pray that I be as good a messenger of his (God's) will as possible. And then, of course, I pray for personal strength and for forgiveness"

George Bush,
US president

On issues such as gay marriage and abortion, Bush has taken generally taken positions consistent with the values of his Christian conservative base.

In 2001, the White House created the Office of Faith-based and Community Initiatives, a program that authorised federal funding to religious charities in an effort to tackle poverty and other social problems.

Bush has never been shy about referring to religion in public. A recent article in Time magazine described him as "the most openly devout president in recent years".

In Plan of Attack, the new book by Washington Post reporter Bob Woodward about the run-up to the US-led war in Iraq, Bush made it clear that his religion was a part of his political identity.

Though he did not say the invasion of Iraq was religiously motivated, he acknowledged the influence of his Christian faith on his own personal sense of justice.

"Going into this period, I was praying for strength to do the Lord's will ... I'm surely not going to justify war based upon God. Understand that," Bush told Woodward.

"Nevertheless, in my case, I pray that I be as good a messenger of his will as possible. And then, of course, I pray for personal strength and for forgiveness," Bush added.

The altar boy

Although Kerry is a former altar boy who has described himself as a "believing and practicing Catholic", he has been less vocal about his faith on the campaign trail than Bush.

Wolfe said this reflected "the difference between evangelical Protestantism and Catholicism". Catholics, in general, "Don't talk about [faith] in public that much," he said.

Analysts say Kerry needs to be
more explicit about his faith

Nevertheless, Kerry will surely attempt to close what some experts refer to as the "God gap" between Democrat and Republican candidates.

"I'm sure that John Kerry will be sure to be seen coming out of Church several times ... He's not going to let Bush monopolise this," Wolfe said.

Lugo said Kerry must demonstrate a religious side to his campaign if he hopes to attract independent voters in key states such as Ohio, Michigan and Florida.

"Kerry will need to be a bit more explicit about his faith in order to fight for those swing votes," he said.

Subject of debate

Kerry has already been the subject of debate among some Catholic officials, some of whom criticised the senator's positions on abortion rights and stem cell research.

Kerry is pro-choice and recently voted against a bill that would make harming a fetus during a crime a separate criminal act. He supports stem-cell research for scientific and medical purposes.

"I think [Bush] will gain some Jewish votes, but not many, and he will lose the Muslim vote because of it, which is much more important"

Alan Wolfe,
Director of The Boisi Center for Religion and American Public Life

One Catholic archbishop in St Louis said Kerry should be denied communion for taking positions officially opposed by the Catholic Church. Whether such condemnations will harm Kerry with Catholic voters is unclear, but Wolfe said probably not.

"Most Catholics share Kerry's position on these issues," he said.

With the November election expected to be close, Jewish and Muslim voters could also have a significant impact in battleground states, experts said.

Although Democrats have enjoyed a strong hold on the Jewish vote for years, some analysts said the president's recent concessions to Israel on the peace process could attract some conservative Jews who favor a decisively pro-Israel policy.

Such gains among Jewish voters, however, could cost Bush in the Muslim community, Wolfe said.

Although Bush won the Muslim vote in 2000, his support appears to have declined significantly in the post-9/11 era of The Patriot Act, immigration reform and the war in Iraq, experts said.

By conservative estimates, there are more than six million Muslim Americans and more than five million Jewish Americans.

"I think [Bush] will gain some Jewish votes, but not many, and he will lose the Muslim vote because of it, which is much more important," Wolfe said.