COLLEGE STATION, Texas - Republican presidential candidate Mitt Romney, seeking to allay suspicions about his Mormon faith, pledged yesterday to serve the common good rather than a single religion if elected president.

"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," Romney told an audience at the George H.W. Bush Presidential Library. "Their authority is theirs, within the province of church affairs, and it ends where the affairs of the nation begin."

The former Massachusetts governor, in a long-awaited speech that could be critical to his hopes of winning the GOP nomination and the White House, went on to say that, as president, he would 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."

But he was equally emphatic in arguing that religion has a place in public life. Saying the doctrine of separation of church and state had been carried too far, Romney said some people or institutions have pushed to remove "any acknowledgment of God" from the public domain. "It is as if they are intent on establishing a new religion in America - the religion of secularism," he said. "They are wrong."

Romney's address, widely compared to one John F. Kennedy gave in Houston in 1960 as he was seeking to become the first Roman Catholic president, was the most important of his political career and came at a potential turning point in the wide-open Republican nomination battle. Romney has sought to cast himself a committed conservative, but many polls have shown resistance, particularly among evangelical Christians, to a Mormon candidate.

Romney has counted on victories in Iowa and New Hampshire to launch a candidacy. Now, in Iowa, he faces growing competition for the votes of Christian conservatives from former Arkansas Gov. Mike Huckabee, an ordained Baptist minister who has made his religious faith central to his candidacy.

As a result, Romney's challenge yesterday was different from Kennedy's in 1960, and so was his speech. Like Kennedy, he sought to neutralize concerns that the Mormon Church would in some way dictate his decision as president. But unlike Kennedy he needed to assure Christian conservatives that they shared fundamental convictions and a determination not to see religion's role in political life reduced.

The setting of the Bush library on the campus of Texas A&M conveyed a presidential aura to the event. Former President Bush introduced Romney, and while he said he was not endorsing any candidate in the GOP race, he nonetheless spoke warmly about Romney and his family.

The audience included several prominent religious leaders, and their immediate reactions were positive.

"His delivery was passionate, and his message was inspirational," Focus on the Family founder James Dobson said in a statement. "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."

Romney will not know whether he succeeded in addressing those concerns until the first results come in from Iowa on Jan. 3, where religious conservatives play a substantial role in that state's GOP caucuses.

To those Christians, Romney offered a statement of his own beliefs: "I believe that Jesus Christ is the son of God and the savior of mankind." But Romney declined to attempt to demystify the teachings of the Mormon Church. "No candidate should become the spokesman for his faith," he said. "For if he becomes president, he will need the prayers of the people of all faiths."

Romney, like Kennedy, said there should be no religious test for the presidency. But he also explicitly declined to distance himself from his church. "I believe in my Mormon faith, and I endeavor to live by it," he said. Should he lose because of that, "so be it."

Romney underscored repeatedly the religious heritage that was at the heart of the founding fathers' vision of the new country. And he said Americans should focus on their shared moral values rather than on the denominational differences that sometimes divide the country.