That’s a dramatic spike in false views about the president’s religious faith — and it comes in a poll taken before Obama weighed in on plans to build a mosque two blocks from ground zero.

In a Pew poll taken last March, only 17 percent of Republicans said that Obama was a Muslim. Now, 31 percent hold that false belief.

While Pew’s new poll finds that people who disapprove of Obama’s job performance are more likely to consider him a Muslim, false beliefs about the president’s faith aren’t limited to Republicans. Eighteen percent of the independents polled said Obama is a Muslim, an 8-point increase since last year.

Only 10 percent of Democrats polled said Obama is a Muslim, but even that’s up 3 percentage points since March 2009. And only 46 percent of Democrats correctly identify Obama as a Christian — down 9 percentage points since last March.

During the presidential campaign, Obama — whose father was raised as a Muslim — repeatedly found his faith questioned, most often in smear e-mails that suggested he was born in Kenya, not Hawaii, and harbored a secret Islamist agenda.

Obama confronted the rumors head-on during a debate in January 2008. “Let’s make clear what the facts are: I am a Christian,” he said then. “I have been sworn in with a Bible. I pledge allegiance and lead the Pledge of Allegiance sometimes in the United States Senate when I’m presiding.”

The Obama campaign’s “Fight the Smears” website also tried to knock down the rumors, explaining that Obama is a “committed Christian” who was “sworn into the Senate on his family Bible” and “regularly attended church with his wife and daughters for years.” “When people fabricate stories about someone’s faith to denigrate them politically, that’s an attack on people of all faiths,” the campaign’s website said.

Still, more than a year into Obama’s presidency, his faith remains a mystery for many. Only 34 percent of Pew’s respondents identified Obama as Christian — down 14 percentage points since last year. And 43 percent said they don’t know what Obama’s religion is.

The falloff among moderate and liberal Republicans was particularly striking. In March 2009, 53 percent of moderate and liberal Republicans identified Obama as a Christian. Now only 26 percent do.

Either way, only a relatively small minority of Americans believe Obama is relying too much on his religious views as he does his job. Eleven percent of Pew’s respondents said Obama relies too much on his religious beliefs, while 48 percent said he relies on them the right amount and 21 percent said he relies on them too little.

The poll, conducted by the Pew Research Center for the People & the Press and the Pew Research Center’s Forum on Religion & Public Life, was taken between July 21 and Aug. 5.