Romney appears to be making some headway. Several prominent evangelical leaders said that, after meeting him, they had grown sufficiently comfortable with the notion of Romney as president to overcome any concerns they might have about his religion.

On a pragmatic level, some said that Romney — despite questions among conservatives about his shifting views on abortion and gay rights — struck them as the Republican candidate best able to win and carry their social conservative agenda to the White House.

"There's this growing acceptance of this idea that Mitt Romney may well be and is our best candidate," said Jay Sekulow, the chief counsel for the American Center for Law and Justice, a conservative legal advocacy group, and a prominent host on Christian radio.

Mark DeMoss, an evangelical public relations consultant who represents many conservative Christian organizations, said it was "more important to me that a candidate shares my values than my faith," adding: "And if I look at it this way, Romney would be my top choice."

Mormons consider themselves to be Christians, but some beliefs central to the LDS Church are regarded by other churches as heretical. For example, Mormons have three books of Scripture other than the Bible, including the Book of Mormon, which they believe was translated from golden plates discovered in 1827 by Joseph Smith Jr., the church's founder and first prophet.

They believe that Smith rescued Christianity from apostasy and restored the church to what was envisioned in the New Testament — but these doctrines are beyond the pale for most Christian churches.

Beyond that, there are perceptions among some people regarding the LDS Church that account for at least some of the public unease: that Mormons still practice polygamy (the church renounced polygamy in 1890), that it is more of a cult than a religion, and that its members take political direction from the church's leaders.

Several Republicans said such perceptions could be a problem for Romney, especially in the South, which has had a disproportionate influence in selecting Republican presidential nominees.

Gloria A. Haskins, a state representative from South Carolina who is supporting Sen. John McCain for the Republican nomination, said discussions with her constituents in Greenville, an evangelical stronghold, convinced her that a Mormon like Romney could not win a Republican primary in her state. South Carolina has one of the earliest, and most critical, primaries next year.

"From what I hear in my district, it is very doubtful," Haskins said. "This is South Carolina — we're very mainstream, evangelical, Christian, conservative. It will come up — in this of all states, it will come up."