DALLAS (Reuters) - In a U.S. election campaign where presidential candidates from both major parties have talked openly about their Christian faith, some non-Christians feel shut out or turned off.
Despite the constitutional separation of church and state, religion plays a big and sometimes decisive role in politics in America, where levels of belief and regular worship are far higher than those in Europe.
"Non-Christians are concerned that they will be excluded from the process," said Ahmed Rehab, a spokesman with the Council on American-Islamic Relations.
"I welcome faith values if they inspire candidates to do good things. But I worry if it is used as a litmus test to include someone in political participation."
About 75 percent of the U.S. population, long a melting pot of immigrants from around the world, identifies itself as Christian, according to several estimates.
That is a huge but divergent source of potential votes for Republican and Democratic candidates in their long contest for the nomination to run for the White House in the November election.
U.S. politicians are not shy of talking about their religion and regularly appear in church.
In recent decades, part of the American political drama has been scripted by the "religious right" -- mostly white evangelical Protestants united by strong opposition to abortion and gay marriage who have been a key base of support for the Republican Party.
Republican hopeful Mike Huckabee, who scooped up strong evangelical support but whose campaign is fading ahead of next Tuesday's nominating contests across the country, is a Baptist preacher who peppers his speeches with Biblical allusions.
Mitt Romney is a Mormon who was moved to address questions about his faith in a speech in December. John McCain has long sought to smooth relations after including leaders of the religious right among those he called "agents of intolerance" during his failed presidential bid in 2000.
The leading Democratic presidential contenders have also been open and candid about their faith.
That faith, and that of the Republican candidates, is Christian, although candidates have also spoken about the need for religious tolerance.
A false rumor that has circulated on the Internet about Democratic candidate Barack Obama, whose father was Kenyan, is that he is Muslim who has lied about his religion. The rumor appears to illustrate the importance some voters attach to a candidate being Christian.
LEAVE RELIGION OUT, SOME SAY
Estimates of the numbers of non-Christians in America vary. Some put the percentage of atheists, agnostics or "unaffiliated" at between 15 and 18 percent of the population of 300 million.
Jews, Muslims, Hindus and people of other religions make up fewer than 10 percent of the population.
Standing in a Hindu temple in a Dallas suburb before statues of his religion's deities, Tejas Karve says he understands why the candidates stress their commitment to Christianity. But it does leave him with a sense of exclusion.
"I think it's geared more towards Christians because that's the majority. It's incomprehensible for them (Americans) to have a candidate who's not Christian," the 26-year-old pilot, who immigrated from India eight years ago, told Reuters.
"I do believe they leave (non-Christians) out to a point."
Political professions of faith leave some unmoved.
"Why is that relevant? Who cares? The great issue is where do we stand on Medicare and Social Security and immigration ... Why inject religiosity into that?" asked Paul Kurtz, chairman of the Council for Secular Humanism.
"Are we (secular humanists and atheists) marginalized? No. Are we turned off? Yes!"
Atheists and agnostics have long been targets of the religious right who see moral decay in secularization.
Some critics say those without a religion were singled out in the speech by Romney in which he sought to ease concerns among Republican evangelicals about his Mormon faith.
He said "freedom requires religion" -- implying that it could not exist without it -- and criticized those who "seek to remove from the public domain any acknowledgment of God ... It is as if they are intent on establishing a new religion in America -- the religion of secularism. They are wrong."
A Pew Research Center survey last year found that 63 percent of those polled said they would be "less likely" to support a presidential candidate who did not believe in God.
But those who say they are "unaffiliated" or atheist are very keen to cast their ballots. Pew data shows that 82 percent of them are very or somewhat likely to vote. At 90 percent, evangelicals are the only group more likely to vote.