WASHINGTON (Reuters) - The religious faiths of President Barack Obama and Republican challenger Mitt Romney will have little weight in November's presidential election, a poll showed on Thursday.

Sixty percent of voters are aware that Romney is a Mormon, and 81 percent say it does not matter to them, according to the poll by the Pew Research Center. The awareness level is almost unchanged from four months ago, during the Republican primary elections.

"Unease with Romney's religion has little impact on voting preferences," the Pew report said.

"Republicans and white evangelicals overwhelmingly back Romney irrespective of their views of his faith, and Democrats and seculars overwhelmingly oppose him regardless of their impression."

The United States has never had a Mormon president.

Obama is a Christian but the view that he is Muslim persists almost four years into his presidency, with 17 percent of voters saying he is Muslim. Forty-nine percent say he is Christian, down from 55 percent near the end of his 2008 campaign, and 31 percent say they do not know Obama's religion.

Among conservative Republicans, 34 percent say Obama, a Democrat, is Muslim, the poll showed.

Overall, 45 percent of voters are comfortable with Obama's religion, 5 percent say it does not matter and 19 percent are uncomfortable.

About two-thirds of voters - 67 percent - agree with the statement "It's important to me that a president have strong religious beliefs." The level has changed little in the past decade.

But 66 percent oppose churches or other houses of worship endorsing political candidates.

The telephone survey was carried out by Pew's Forum on Religion & Public Life and the Pew Research Center for the People & the Press from June 28 to July 9.

The poll sampled 2,973 adults, including 2,373 registered voters. The margin of error for adults was 2.1 percentage points and 2.3 percentage points for voters.