COLLEGE STATION, Texas -- His campaign at a crossroads, Republican Mitt Romney said Thursday his Mormon faith should neither help nor hinder his quest for the White House and vowed to serve the interests of the nation, not the church, if elected president.

"When I place my hand on the Bible and take the oath of office, that oath becomes my highest promise to God," Romney said in a speech that explicitly recalled remarks John F. Kennedy made in 1960 in an effort to quell anti-Catholic bias.

After declining for months to address the issue of his Mormonism directly, Romney switched course as polls showed widespread unease about his religion and showed him losing his once-sizable lead in the opening Iowa caucuses to Mike Huckabee, a Baptist minister and former governor of Arkansas.

Romney said some believe a forthright embrace of his religion will "sink my candidacy. If they are right, so be it. But I think they underestimate the American people."

"Americans tire of those who would jettison their beliefs, even to gain the world," he said.

The Jan. 3 Iowa caucuses provide the first test of the race for the White House, followed closely by the Jan. 8 primary in New Hampshire. Romney has campaigned and spent energetically in both states in hopes of gaining unstoppable momentum for the rush of elections that will soon follow.

A defeat in Iowa would be particularly difficult to absorb, given Huckabee's shoestring operation. Polls show Romney's religion is a political drag on his campaign, and Huckabee has risen in surveys by gaining the support of evangelical Christians, who comprise an estimated 40 percent of likely caucus goers in Iowa.

"Let me assure you that no authorities of my church, or of any other church for that matter, will ever exert influence on presidential decisions," he pledged. "Their authority is theirs, within the province of church affairs, and it ends where the affairs of the nation begin."

He added: "If I am fortunate to become your president, I will serve no one religion, no one group, no one cause and no one interest. A president must serve only the common cause of the people of the United States."

Mormons believe that authentic Christianity vanished a century after Jesus and was restored only through Joseph Smith, who founded the religion and is viewed as a prophet by its adherents. Smith revised -- and in his view corrected -- large sections of the Bible in the 19th century, an act of heresy in the eyes of Protestant and Roman Catholic leaders. The Mormon scriptures include the Old and New Testaments, as well as books containing Smith's revelations.

Romney mentioned the word "Mormon" only once, and Huckabee not at all in his speech at the George Bush Presidential Library.

In speaking frankly about his beliefs, he hoped to reassure other Christians about his intent.

"I believe that Jesus Christ is the Son of God and the savior of mankind. My church's beliefs about Christ may not all be the same as those of other faiths," he said, adding that these differences are "not bases for criticism but rather a test of our tolerance."

"Religious tolerance would be a shallow principle indeed if it were reserved only for faiths with which we agree."

He assailed "the religion of secularism" he said was creeping into American life, and drew chuckles from his invited audience as he complained that Europe's picturesque cathedrals are largely empty amid societies "too busy or just too `enlightened' to venture inside and kneel in prayer."

Romney said: "We should acknowledge the Creator as did the founders, in ceremony and word. He should remain on our currency, in our pledge, in the teaching of our history and, during the holiday season, nativity scenes and menorahs should be welcome in our public places."

Steve Scheffler, president of the Iowa Christian Alliance, said, "I think he did what he thought he needed to do to address concerns about whether he might use his particular faith as the basis for his decisions as president."

James Dobson, founder of Focus on the Family, called Romney's speech "a magnificent reminder of the role religious faith must play in government and public policy." He added, "Whether it will answer all the questions and concerns of evangelical Christian voters is yet to be determined, but the governor is to be commended for articulating the importance of our religious heritage as it relates to today."

The Rev. Welton Gaddy, president of the Interfaith Alliance, said, "While I may disagree with some of the points made in the speech, including his lack of acknowledgment of the values and contributions of the nonreligious among us, I appreciate the overall tone."

Among the critics was Costas Panagopoulos, a political-science professor at Fordham University.

"Make no mistake about it, this was a political speech," Panagopoulos said. "Romney sounded like he is running for pastor-in-chief rather than commander in chief."

Romney's rivals generally steered clear of commenting on the speech, but agreed that Romney's religion has no bearing on whether he would make a good president.

"It has nothing to do with what faith a person has -- it's whether or not that person's life is consistent with how he lives it," Huckabee said on NBC's "Today" show.

Rudy Giuliani, a Catholic, said there should be no religious test for office.

"We're a country that is based on religious freedom, and we're a country in which we respect each other's right to have different views about religion, about God, about our belief in God," Giuliani said during an appearance in Sarasota, Fla. "I think the governor made that point very clearly today. I can't imagine anybody disagreeing with that."

While Romney has been subject to some leafleting and phone calling pointing to religious differences between his faith and others, he has faced little outright religious bigotry or questions on the campaign trail.

Yet, in an AP-Yahoo poll last month, half said they had some problems supporting a Mormon presidential candidate, including one-fifth who said that would make them very uncomfortable.

Fifty-six percent of white evangelical Christians -- a major portion of likely participants in the early GOP presidential contests in Iowa and South Carolina -- expressed reservations about a Mormon candidate.

Romney sought to allay those concerns by confronting them, and his remarks received wide attention. His staff released favored excerpts before the network morning shows and distributed photos of him editing his remarks, much as the White House does before a State of the Union speech.

And Romney chose a presidential library, with a backdrop of 10 flags and the presidential seal, for his speech.

Former President Bush introduced him, noting his own connection to Romney's late father, former Michigan Gov. George Romney.

"He's certainly one of my mentors when it comes to points of light," said Bush, who enacted a volunteer initiative while president called, "Thousand Points of Light."

That said, Bush said he had no intention of endorsing anyone. "I simply have too much respect for all of the candidates," he said.

Striking a family chord, Romney's wife of 38 years, Ann, and four of the couple's five sons sat in the front row for the speech -- two with their own children.

"We are a long way from perfect, and we have surely stumbled along the way, but our aspirations, our values, are the selfsame as those from the other faiths that stand upon this common foundation," Romney said. "And these convictions will indeed inform my presidency."

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Associated Press Writer Alan Fram in Washington contributed to this report.