DES MOINES, Iowa — Republican presidential candidate Mitt Romney, striving to be the country's first Mormon president, will give a speech this week explaining his relatively unknown faith to voters, his campaign said Sunday.

The decision, made after months of debate at his Boston headquarters over whether to make a public address about his religion, comes as the former Massachusetts governor's bid is threatened in Iowa by underdog Mike Huckabee. The ex-governor of Arkansas and one-time Southern Baptist minister has rallied influential Christian conservatives to erase Romney's monthslong lead and turn the race into a dead-heat.

Romney will deliver a speech called "Faith in America" at the George Bush Presidential Library in College Station, Texas, on Thursday, outlining his religious beliefs and how they might impact his administration.

"This speech is an opportunity for Governor Romney to share his views on religious liberty, the grand tradition religious tolerance has played in the progress of our nation and how the governor's own faith would inform his presidency if he were elected," Kevin Madden, a campaign spokesman, said in a statement. "Governor Romney understands that faith is an important issue to many Americans, and he personally feels this moment is the right moment for him to share his views with the nation."

Madden stressed that Romney made the decision last week and that the venue doesn't not indicate that Bush is endorsing Romney.

The Texas site — and speech itself — recalls the address John F. Kennedy made in Houston as he sought to explain his faith during the 1960 campaign and become the first Catholic president.

From the start of Romney's bid, his Mormon faith has been an issue in the campaign as he tried to position himself as the candidate of the GOP's family values voters. A Pew Research Center poll in September found a quarter of all Republicans — including 36 percent of white evangelical Protestants — said they would be less likely to vote for a Mormon.

Indeed, skepticism about his religion has proven difficult for Romney to overcome, particularly in Iowa where religious conservatives play a powerful role in GOP caucuses. Romney has invested heavily in the state, hoping to use a win here as a launching pad to the nomination.

Polls show the race a toss up. Just a month ago Romney held a wide lead and Huckabee trailed in the single digits. Huckabee has surged in large part by rallying the GOP's religious right wing.

Last week, Huckabee sought to exploit Romney's weaknesses — his Mormon faith and his reversal on abortion as well as shifts on other issues — by running a TV ad in Iowa that emphasizes his own religious beliefs. The ad doesn't mention Romney but clearly targets him.