By Dan Gilgoff, CNN Belief Blog Co-Editor

President Barack Obama gave an unusually personal speech about his religious faith on Thursday, saying that "it is the biblical injunction to serve the least of these that keeps me going and keeps me from being overwhelmed," in address to a prayer breakfast in Washington.

The speech, delivered at the National Prayer Breakfast, comes on the heels of public opinion surveys that show only a minority of Americans know that Obama is a Christian and that a growing number believe he's a Muslim.

"My Christian faith has been sustaining for me over the last couple of years and even more so when Michelle and I hear our faith questioned from time to time," the president said Thursday, referring to his wife. "We are reminded that ultimately what matters is not what other people say about us but that we are true to our conscience and true to our God."

"When I wake in the morning, I wait on the Lord, I ask him to give me the strength to do right by our country and our people," Obama said later. "And when I go to bed at night, I wait on the Lord and I ask him to forgive me my sins and to look after my family and to make me an instrument of the Lord."

The address was televised and streamed live on the White House website.

The White House denied that the speech is a response to public misperceptions about Obama's religion.

"He's a committed Christian, one who takes his faith very seriously," said a White House official before the speech. "There may be misunderstanding and some folks who attack his faith, but at the end of the day the American people know who he is and where he stands."

A major survey last fall, however, showed that a substantial and growing number of Americans believes that Obama - a self-described Christian - is Muslim.

Nearly 1 in 5 Americans believes Obama is a Muslim, up from about one in 10 Americans who said he was Muslim in 2009, according to the survey. It was conducted in July and August by the Pew Forum on Religion and Public Life.

Fewer than half of Democrats and African-Americans, core components of Obama's political base, correctly identified Obama as Christian.

The Rev. Joel Hunter, a Florida minister who is close to the president and was consulted about parts of Obama's Thursday speech, says he has encouraged Obama to open up about his faith.

"He needs to openly declare himself a Christian and not settle for people's skepticism at that point," said Hunter, who leads an evangelical church in Orlando. "All of us ought to be able to say who we are and taken for our word. It's frustrating because he still has some people questioning his faith."

Hunter says that he and the White House were caught off-guard by the results of last year's Pew survey on Americans' views of Obama's religion.

On Thursday, Obama spoke at length about his prayer life, saying his prayers fall into three categories: for those who are struggling, for personal humility, and to be closer to God.

"Faith reminds me that in spite of being one very imperfect man I can still help whoever I can, however I can, wherever I can for as long as I can," Obama said of the first kind of prayer, "and that somehow God will buttress these efforts."

"The second recurring theme in my prayer is a prayer for humility," Obama said later. "God answered the prayer early on by having me marry Michelle."

"The challenge is to balance this uncertainty and humility with a need to fight for deeply held convictions," he continued. "I pray for this wisdom very day. I pray for God to show me and all us the limits of our understanding."

With regard to his third kind of prayer, Obama said the recurring theme "is that I might walk closer to God and make that walk my first and most important walk."

The White House believes that some of the ignorance about the president's faith is the result of a misinformation campaign against him.

"Under the radar there are of course those who would not tell the truth about him," said the White House official, who would not speak for attribution. "There are folks who have a misunderstanding of the president's faith and who repeat that misunderstanding."

But Hunter said that the speech was as much a product of Obama settling into office and feeling more comfortable about revealing his personal side.

The White House official echoed that point. "He's had a little over two years in office now and he's had some time to reflect on how his faith intersects with public work," the official said. "He's had the time to make those reflections."

The National Prayer Breakfast has been an annual Washington event for 58 years.

Obama had been a member of Chicago's Trinity United Church of Christ in Chicago until spring 2008, when he left after videos surfaced showing his pastor, the Rev. Jeremiah Wright, delivering controversial sermons about the United States.

U.S. Rep. Gabrielle Giffords' husband will speak at the breakfast on the congresswoman's behalf, her office announced Wednesday.

Capt. Mark Kelly, a NASA astronaut, will deliver the closing prayer at the event, the Arizona congresswoman's office said in a statement.

Authorities say Giffords was the primary target of a shooting that left six people dead and 13 injured in Tucson, Arizona, on January 8.