Almost two in 10 registered voters believe the president is Muslim, while more than three in 10 say they do not know the president's religion.

Among self-identified Republicans, 30 percent believe the president is a Muslim, double the number of those who identified the president's faith incorrectly in 2008. That figure is double what it was in 2008.

The uncertainty surrounding the president's beliefs could be an electoral liability in 2012. Only 45 percent of voters say they are "comfortable" with the president's faith.

But more likely is that voters simply aren't concerned with their candidate's religious faith in a year dominated by economic issues.

“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 report said.

And those most informed about each candidate's religious faith are those most likely to be comfortable with their religious preferences.

The margin of error of the survey is plus or minus 2.1 percentage points.