COLLEGE STATION, Texas — Moving to win over Christian conservatives wary of his Mormon faith, Republican Mitt Romney said Thursday his religion shouldn't preclude him from being president and wouldn't dictate his decisions if elected.

"I will serve no one religion, no one group, no one cause and no one interest," Romney said in a speech that comes as Mike Huckabee has gone ahead in polls in Iowa with strong support from evangelicals.

Christian conservatives who heard Thursday's speech at the George Bush Presidential Library generally gave Romney good marks. But the test of whether the former Massachusetts governor can win over religious conservatives won't come until the Iowa presidential caucuses next month.

About 39 percent of likely GOP Iowa caucus-goers describe themselves as evangelicals, and many of them say they would be reluctant to vote for a Mormon.

Richard Land of the Southern Baptist Convention, who has not endorsed a candidate in the race, said the speech "won't hurt" in efforts to attract faith-based voters.

"He certainly helped himself with some evangelicals. But let's remember, Kennedy didn't convert all Protestants" with his 1960 speech on religion and politics, said Land, who was among guests invited by the Romney camp.

Lou Sheldon, chairman of the Traditional Values Coalition and a Romney supporter, called the speech "a defining moment" for the campaign.

"I now have enough ammunition to silence the criticism of an unbelievable number of these friends of mine," he said.

But Florida televangelist Bill Keller, reflecting an anti-Mormon streak among some religious conservatives, said the speech isn't enough to convince those who believe Mormonism is a cult.

The Romney campaign had debated for months whether to confront questions about the candidate's religion, much as John F. Kennedy did 47 years ago in his speech to Protestant ministers in Houston.

Kennedy's task then was to reassure voters that the Vatican would not exert influence on his decisions as president. He emphasized a high wall between religious faith and public action.

Romney's mission was different. Christian conservatives, who make up a crucial voting bloc in the Republican Party, want religious faith to inform the decisions of their political leaders.

In his 20-minute address, in which he was introduced by former President George H.W. Bush and framed by a phalanx of American flags, Romney reassured evangelicals that he would not be taking orders from his church but declared that their shared religious values would have a place in his administration.

"I will take care to separate the affairs of government from any religion, but I will not separate us from the God who gave us liberty," he said.

"There are some," he said, who "would prefer it if I would simply distance myself from my religion, say that it is more a tradition than my personal conviction, or disavow one or another of its precepts. That I will not do."

The Rev. Barry Lynn of Americans United for Separation of Church and State objected to Romney's description of the role of religious faith in government.

"I was particularly outraged that Romney thinks that the Constitution is somehow based on faith and that judges should rule accordingly," he said. "That's a gross misunderstanding of the framework of our constitutional system."

Romney has staked out conservative positions on abortion and gay marriage, but polls indicate that a quarter of evangelicals would be reluctant to vote for a Mormon.

Romney called that a religious test, which the founders prohibited in the Constitution.

"No candidate should become the spokesman for his faith. For if he becomes president, he will need the prayers of the people of all faiths," he said.

Romney's speech lasted about 20 minutes and was interrupted a dozen times by applause from the invited audience of several hundred people. He said the word "Mormon" only once, otherwise referring to "my religion," "my faith" and "my church."

He said he believes Jesus "is the son of God and savior of mankind," but acknowledged Mormon doctrine has different beliefs about the earthly presence of Jesus Christ. Some evangelicals are troubled that Mormons believe Jesus visited America and that the Bible is insufficient as a religious text.

Romney said those differences should not be "bases for criticism, but rather a test of our tolerance."

Unlike Thursday's speech in which Romney faced a friendly crowd, Kennedy spoke in 1960 to a group openly in opposition to having a Catholic as president.

The Alabama and Texas Baptist conventions, the National Association of Evangelicals and the president of the Southern Baptist Convention all came out in opposition. On Sept. 7, 1960, a group of 150 conservative Protestant leaders issued a statement warning that Kennedy would be "would be under extreme pressure from the hierarchy of his church to accede to its policies."

Kennedy delivered his speech five days later.