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 that 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.