( L - R Romney , Giuliani

DALLAS, (Reuters):

b>When a pair of Mormon missionaries knocked at the door of Jerry Pierce's home in a north Dallas suburb last month, he marshalled his arguments and stood his ground.

"I look forward to encounters like that. I like to talk to them about the nature of Christ and who Jesus is," said Pierce, a staunch Southern Baptist, the biggest Protestant denomination in the United States.

Mitt Romney, a Mormon, is running into similar resistance as he tries to win over Southern Baptists and other evangelical Protestants in the race for the Republican Party's nomination for the 2008 U.S. presidential election.

Mormon faith

Romney will need the support of this traditional Republican base if he is to take on former New York mayor Rudy Giuliani, who is running strongly in opinion polls despite his three marriages and a pro-abortion position that is anathema to many Republicans.

The reason Romney faces difficulties with Southern Baptists, according to many experts, is his Mormon faith. Not only do many Southern Baptists regard the Mormon church as a cult, they also regard it as a competitor that is winning - or poaching - converts from among the evangelical flock.

"There are now more Mormons that used to be Southern Baptist than any other denomination," said Dr. Richard Land, president of the Ethics & Religious Liberty Commission of the Southern Baptist Convention, a 16-million strong group.

"As a consequence, Southern Baptists and other evangelicals have taught their people what Mormons believe and why it's beyond the boundaries of the Christian faith, to inoculate them against those Mormon missionaries," he told Reuters.

This is no small matter for people who take their faith as seriously as Southern Baptists do, and to counter the perceived threat they teach their members in Sunday School to be ready for that knock at the door and be wary of Mormon missionaries.

Romney himself did missionary work overseas.

Dim prospect

Some say a Mormon in the White House would help the faith - founded in 1830 in New York state by Joseph Smith and still struggling with the legacy of polygamy - become more accepted. This is a dim prospect for evangelical leaders, who see themselves competing with the religion, literally, for souls.

"Many evangelicals do not want to see Mormonism mainstreamed," said Matthew Wilson, a political scientist at Southern Methodist University in Dallas.