The number of Americans who believe -- wrongly -- that President Obama is a Muslim has increased significantly since his inauguration and now accounts for nearly 20 percent of the nation's population.

Those results, from a new Pew Research Center survey, were drawn from interviews done before the president's comments about the construction of an Islamic cultural center near Ground Zero, and they suggest that there could be serious political danger for the White House as the debate continues.

(Video: The bloggers and the mosque debate)

The president's religion, like his place of birth, has been the subject of Internet-spread rumors and falsehoods since before he began his presidential campaign, and the poll indicates that those rumors have gained currency since Obama took office. The number of people who now correctly identify Obama as a Christian has dropped to 34 percent, down from nearly half when he took office.

White House officials expressed dismay over the poll results. Faith adviser Joshua DuBois blamed "misinformation campaigns" by the president's opponents.

"While the president has been diligent and personally committed to his own Christian faith, there's certainly folks who are intent on spreading falsehoods about the president and his values and beliefs," DuBois said.

DuBois said the president's Christian faith plays an "important part" in his daily life. And he pointed to six speeches on faith that the president has given in which he talked about his beliefs. But Dubois said coverage of Obama's Christianity has been scant compared with news about the economic crisis, legislative battles and other issues.

(Interactive: The view from Ground Zero)

Among those who say Obama is a Muslim, 60 percent say they learned about his religion from the media, suggesting that their opinions are fueled by misinformation.

But the shifting attitudes about the president's religious beliefs could also be the result of a public growing less enamored of him and increasingly attracted to labels they perceive as negative. In the Pew poll, 41 percent disapprove of Obama's job performance, compared with 26 percent disapproval in its March 2009 poll.

More than a third of conservative Republicans now say Obama is a Muslim, nearly double the percentage saying so early last year. Independents, too, are now more apt to see the president as a Muslim: Among independents, 18 percent say he is a Muslim, up eight percentage points.

(FAQ: The mosque near Ground Zero)

Those numbers come as Obama and other Democrats try to minimize potential fallout from the president's remarks on Friday about the Islamic center in New York. A new Time-SRBI poll found that 61 percent of Americans oppose building the center. Nearly twice as many people said the center, and the mosque inside it, would be an insult to 9/11 victims than said it would be a symbol of religious tolerance.

In the Time poll, 25 percent say most Muslims in the United States are not patriotic Americans. But the survey also indicates that the public's opposition to the center may be more complicated than just anti-Muslim sentiment. Fifty-five percent said they would accept a Muslim community center and place of worship two blocks from their own home.

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