Stalwart conservatives who support the Romney-Ryan ticket, like Representative Louie Gohmert, Republican of Texas; Rick Santorum, a former senator and Republican presidential candidate; and retired Lt. Gen. William Boykin, have appeared on Mr. Beck’s program not so much to tout Mr. Romney directly as to discuss hot-button political issues like the handling of the attack on the United States mission in Benghazi, Libya.

Mostly Mr. Beck has helped Mr. Romney by directly addressing his devout Mormon faith, something the candidate himself rarely does. “I believe Mr. Romney prays on his knees every day,” Mr. Beck said recently on his radio program. “I believe he is being guided.” He has also said that a Romney victory would be “a sign from God.”

Mr. Romney already enjoys a commanding lead among white evangelical Protestant voters — 76 percent to 17 percent for President Obama, according to a Pew Forum on Religion and Public Life survey released on Monday, and 54 percent to Mr. Obama’s 39 percent among Protestant voters. Influential Christian leaders including the Rev. Billy Graham and Ralph Reed have endorsed Mr. Romney.

But deep-rooted tensions between Mormons and evangelical Christians persist, and could affect the turnout on Tuesday, several evangelical leaders said.

“Romney has staked out issues that are aligned with evangelicals,” said Bryan Fischer, director of issue analysis for the conservative nonprofit American Family Association. But, he added, Mr. Romney’s faith may ultimately present a problem in the voting booth. “It’s still an issue for some evangelicals and may influence their voting decision on Nov. 6,” he said. “There are a number of evangelicals who will not vote for someone who doesn’t adhere to orthodox Christianity.”

Mr. Beck and Mr. Romney’s relationship dates to before the presidential campaign when they crossed paths from time to time at events in Salt Lake City. In 2009, Mr. Romney called Mr. Beck “my friend and a statesman in his own right” when he announced Mr. Beck via video at a fund-raiser for George Wythe University.

Born a Roman Catholic, Mr. Beck, 48, converted to the Church of Jesus Christ of Latter-day Saints in 1999 just before he married his second wife, Tania. His personal story of born-again transformation from drug addict and alcoholic to best-selling inspirational author, as well as his rants against big government, made him a favorite among Tea Party conservatives.