Republican candidate Mitt Romney told an audience in Texas Thursday that there should be no religious test for the presidency and those who question his beliefs violate the spirit of the country's founding.

Romney, in a speech at the George Bush Presidential Library, sought to confront skeptics among some evangelical Christians about his Mormon faith as he has surrendered his Iowa lead in some polls to Mike Huckabee, a former Baptist minister and ex-governor of Arkansas.

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

He made reference to the speech John F. Kennedy gave during the 1960 presidential campaign to Southern Baptist leaders who were suspicious about his Catholicism and promised that he "will put no doctrine of any church above the plain duties of the office and the sovereign authority of the law."

The former Massachusetts governor, 60, also said that religion must not be totally removed from public life and that the founding fathers' concept of separation of church and state "has been taken by some well beyond its original meaning" in recent years.

"Freedom requires religion just as religion requires freedom," he said.

Romney said he wouldn't engage in a theological discussion about specific Mormon doctrines. "To do so would enable the very religious test the founders prohibited in the constitution," he said. "No candidate should become the spokesman for his faith."

Romney was given a brief introduction by former President George H.W. Bush, whose library is located on Texas A&M campus in College Station, Texas. Bush insisted that he wasn't endorsing anyone and said he expects "several more candidates to visit, including some on the other side of the aisle."

While some state polls and anecdotal evidence suggest his Mormon faith is a stumbling block, particularly with religious voters, 73 percent of those surveyed in a Bloomberg News/Los Angeles Times poll say it makes no difference in deciding their vote.

To win the Republican nomination, Romney needs to court the church-going voters who make up almost 30 percent of the party's electorate. For several months, evangelical leaders have urged him to talk about his faith, much as Kennedy did when he appeared before the Greater Houston Ministerial Meeting. In many ways, Romney faces a tougher task than Kennedy did.

While mentioning Mormonism only once during the speech, Romney said he wouldn't disavow his faith. He acknowledged that "some believe that such a confession of my faith will sink my candidacy," and he seemed willing to suffer the consequences. "If they are right, so be it."

He insisted that "Americans do not respect believers of convenience. Americans tire of those who would jettison their beliefs, even to gain the world."

Married to the same woman for 38 years and a grandfather of 10, Romney presents himself as a model of Christian family values. Still, evangelicals have said they remain skeptical for two reasons: a faith they consider a cult and a record as governor of Massachusetts that includes support for abortion and gay rights.

Romney cited his faith as "common creed of moral convictions," while acknowledging theological differences. "Whether it was the cause of abolition, or civil rights, or the right to life itself, no movement of conscience can succeed in America that cannot speak to the convictions of religious people."

Contributing: Christopher Stern