WASHINGTON — In an echo of John F. Kennedy's election-eve address on Catholicism 47 years ago, former Massachusetts Gov. Mitt Romney sought to allay concerns Thursday over his Mormon faith before an audience of invited guests at the George Bush Presidential Library in College Station, Texas.

Without delving into the specifics of Mormon doctrine, Mr. Romney invoked the Founding Fathers in asserting the nation's religious underpinnings, called for religious tolerance, and highlighted the "common creed of moral convictions" within the varied theologies of American churches.

And, just as the future President Kennedy promised in 1960 that he would not accept instruction from the pope, Romney promised that as president he would answer to "no one religion."

"When I place my hand on the Bible and take the oath of office, that oath becomes my highest promise to God," Romney said. "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."

Romney also referenced Article 6 of the Constitution, which states that "no religious test" shall ever be required as a qualification for office.

"There are some who would have a presidential candidate describe and explain his church's distinctive doctrines," Romney said. "To do so would enable the very religious test 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."

The speech comes after months of debate within the Romney campaign over the wisdom of such a move. The Republican candidate has faced persistent reservations by a significant portion of the GOP electorate to voting for a Mormon for president.

He had hoped not to have to deliver such a speech, but decided last week that he should. Romney would have preferred to let his success in business and government, and in turning around the 2002 Olympics, in addition to his picture-perfect family, speak for itself. By waiting until this point in the campaign — less than a month before the first nominating contest, the Jan. 3 Iowa caucuses — he is guaranteed major public attention to his address. But if it backfires, by making Mormonism an even bigger issue, he could damage his political prospects.