Mitt Romney is facing an unexpected challenge in Iowa from rival Mike Huckabee, who has enjoyed a groundswell of support from religious voters, particularly evangelical Christians wary of the clean-cut former Massachusetts governor because of his Mormon religion.

The common worry among evangelicals is that if Romney were to capture the White House, his presidency would give legitimacy to a religion they believe is a cult. Since the LDS church places heavy emphasis on proselytizing — there are 53,000 LDS missionaries worldwide — many mainstream Christians are afraid that Mormon recruiting efforts would increase and that LDS membership rolls would swell.

One such concerned evangelical, Tricia Erickson, was raised in the Mormon faith but left as an adult. She has attended the McLean Bible Church in northern Virginia. Erickson adamantly opposes the LDS church, which she considers a brainwashing cult. She has launched a media blitz designed to discredit Romney based on his religion.

In an interview, Erickson told me that Romney has “got the image. He’s a good business man. He has the coiffed hair with every hair in place. … He has a pretty, blonde Mormon wife; he has a chiseled face. He is very polished. He has that image which Mormons develop through the Mormon Church to present to the public to give credibility to the religion.”

Or take Bill Keller, evangelical host of the Florida-based “Live Prayer TV.” Last year he told his reported 2.4 million e-mail subscribers that a vote for Romney would mean a vote for Satan.

“The presidency is the most powerful position in the world,” Keller explained to me. “If Romney was elected president, it would give mainstream credibility and acceptance to the Mormon cult and lead millions of people into that cult.”

THE ONLY PROBLEM with those fears is that they don’t add up. Evangelicals may be surprised to learn that the growth of church membership in Massachusetts slowed substantially during Romney’s tenure as governor. In fact, one could make the absurdly simplistic argument that Romney was bad for Mormonism.

Consider: From 1997 to 2002, the six years prior to Romney’s governorship, LDS church membership in Massachusetts grew by a rate of nearly 40 percent. During the four years Romney was in office, membership growth slowed to a snail’s pace — a mere 1.7 percent, according to membership statistics kept by the church and published in the LDS Church Almanac. The national growth rate during that same period was about three times the Massachusetts number: 5.1 percent.

During the Romney years, the number of Mormon wards and branches, congregations that are created and dissolved based on geography and population, in the Bay State rose by one and fell by one, indicating that congregational growth was static. Nationwide, the number of congregations grew by 7.3 percent.

When I put these growth rates to both Erickson and Keller, they didn’t dispute the numbers. However, they argued that a Romney presidency would be something else entirely.

Erickson said the Massachusetts stagnancy can be attributed to the liberal nature of the state, where Christianity is declining. However, if Romney won the White House, she argued that Mormons would have an easier time winning converts in the more religious parts of the nation, particularly the South, where church attendance is high.

Keller believes the slowed Massachusetts growth rate is explained by the fact that Massachusetts is a stronghold for Catholics. He claimed these Catholics have grown less willing to listen to Mormon proselytizing but, like Erickson, he fears a Romney presidency will open the floodgates elsewhere.

SUPERFICIALLY, Erickson and Keller’s worries are not crazy. The LDS church has undergone phenomenal growth in the past.

David O. McKay was the ninth prophet and president of the Church, who served from 1951 to 1970. McKay implemented the “every member a missionary” program in 1961 in hopes of spreading the LDS Gospel worldwide, to great effect. Under his tenure, the number of LDS “stakes” — congregational units similar to a Catholic diocese — more than doubled, and total church membership well more than doubled.

Since McKay’s death, subsequent church prophets, apostles, and lay leaders have continued to stress missionary work, particularly singling out lay members of the church as not doing enough to advance the cause. During a 1999 address beamed from Salt Lake City to chapels throughout the world, the current Mormon prophet Gordon B. Hinckley urged members to double the number of people baptized into the Church each year, from 300,000 to 600,000.

However, since Hinckley issued his challenge, the number of church members serving full-time missions has actually decreased, thanks to stricter moral standards church leaders recently created for those seeking to serve missions. True, Church membership has increased, but not to the extent Hinckley had hoped for.

Since Hinckley took over in 1995, membership has grown by about 38 percent, from 9.3 million then to 12.8 million today. The rate is impressive when compared to other religious groups in the United States. However, it has slowed significantly when compared with earlier years of LDS growth. In some places, such as Massachusetts, it has essentially gone flat.

“I don’t know that [the slowed growth rate] has anything to do with [Romney] as much as the conversion rate in America is not moving at the same pace as it was 20 years ago,” said M. Russell Ballard, an LDS apostle who is one of the top-ranking leaders of the church.

Ballard explained that he thought that the problem was much larger: “In a lot of ways, America is drifting a little bit towards religious indifference, similar to what you see in many parts of Europe … [O]ur biggest challenge, to be candid with you, is apathy, is just plain indifference. … [People are] far more interested and worried about the NFL and the NBA than they are about God and their personal purpose in life.”

And while it’s true that many Mormons support Mitt Romney, his candidacy is essentially irrelevant to the larger Mormon project. When I asked one of Ballard’s colleagues, Apostle Quentin L. Cook, whether the church has noticed a Romney “bump,” he said he hasn’t noticed one, and that the question was not one that preoccupied him.

“The missionaries are fully engaged and they’re doing great work. We haven’t done a survey to find out whether there’s been an increase,” Cook said.

ONE WAY TO GAUGE what might happen under a President Romney would be to look at what happened during the period of the 2002 Olympic Winter Games. Held in Salt Lake City, they were dubbed the “Mormon Olympics.”

During this period, majority-Mormon Utah garnered vast international attention as more than 8,700 members of the media converged in the Beehive State to cover the games. Despite a rocky, scandal-ridden start (which was cleaned up largely due to the efforts of one Mitt Romney, who was brought in as president and CEO of the Games), the Games finished with a budget surplus, no major security breaches, and warm feelings all around.

Leaders of the LDS church urged members to avoid overt proselytizing in connection with the Games. They did, however, welcome a vast influx of visitors to Temple Square, where the Mormon Tabernacle Choir sang, talented Brigham Young University dancers performed in its Conference Center, and leaders presented numerous religious and patriotic services.

Despite all the increased attention, worldwide the Church grew only slightly, and in fact in the year leading up to the games the total number of congregations fell. Overall, from 2000 to 2004, there was a 10.9 percent increase in memberships and a 3.6 percent increase in congregations.

These modest growth figures include children of LDS parents, who are traditionally baptized at age 8, as well as converts from other faiths. The numbers suggest that while the public has had increased exposure to Mormons and the Mormon faith, that doesn’t necessarily translate to a large spike in membership.

The LDS church is likely to continue its current modest-but-impressive growth whether or not Romney wins the White House. Perhaps the only real worry for evangelicals is that, if elected, the former Massachusetts governor will demonstrate to Americans that Mormons don’t have horns.