Obama takes part in Sunday service at the Vermont Avenue Baptist church in Washington Photo: REUTERS
The results came days after the US president waded into a bitter dispute over controversial plans to build a mosque near the Ground Zero site of the Sept 11 terrorist attacks in New York.
Speaking at an iftar dinner held at the White House last Friday to mark the breaking of the Ramadan fast, Mr Obama, a practising Christian, weighed in on the "local" issue, affirming the right to build on the grounds of religious freedom, though on Saturday he appeared to backtrack, saying he had not been taking a stand on the "wisdom" of doing so.
Republicans have promised to make Mr Obama's support for the project, which is broadly opposed by a majority of the US public, though supported by a majority of New Yorkers, an issue in the upcoming elections.
On his inauguration day in January 2009, some 11 per cent of Americans believed that Mr Obama was a Muslim. In office, Mr Obama has highlighted the fact that his middle name is Hussein, in part to boost his credibility abroad. His father was a non-observant Muslim and his mother was a Christian-born secularist.
Nearly one in five Americans polled last week - before the president's comments on the New York mosque - believed Mr Obama was a Muslim, according to a poll by the Pew Forum on Religion and Public Life.
But in a poll taken after Mr Obama's remarks, 24 per cent - or nearly one in four - Americans believed he was a follower of Islam. And roughly 30 per cent of those polled for Time magazine said Muslims should be barred from running for president or serving on the US supreme court.
The results will fuel criticism from even fellow Democrats that Mr Obama is failing to communicate effectively who he is, which could prove damaging ahead of November's mid-term elections.
Among those who said Mr Obama is a Muslim, 60 per cent said they learned about his religion from the media. The phenomenon is not limited to Republicans. Among independent voters, 18 per cent said he is a Muslim, up eight percentage points from the start of last year.
Mr Obama has encountered trouble in the past with public perception of his faith, when the radical sermons of his Chicago pastor, Reverend Jeremiah Wright, were publicised just before he clinched the Democratic presidential nomination.
After a much-publicised search for a church to attend in Washington, the White House said Mr Obama had decided that his presence would disrupt an ordinary congregation, and that he would worship privately at Camp David, the president's weekend retreat.
This has meant that he has not been seen attending public worship services as his predecessors were. Polls indicate that well over half of Americans describe themselves as religiously observant and it would be almost unthinkable for a major politician to describe him or herself as an atheist.
Mr Obama's religion and his place of birth have been the subjects of rumours and bogus facts spread via the internet. During his election campaign, Obama aides worked aggressively to rebut these.
But the number of people who now correctly identify Mr Obama as a Christian has dropped to 34 per cent, down from nearly half when he took office. Joshua DuBois, Mr Obama's faith adviser, dismissed the "misinformation campaigns" by Mr Obama'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," he told the "Washington Post".