* Christian conservative leader says has not decided
* Group to meet again on Monday
By Todd Melby and Sam Youngman
DES MOINES/MINNEAPOLIS, Dec 18 (Reuters) - Newt Gingrich's marital problems have come back to haunt him in Iowa where Christian conservatives are split over whether they can look beyond his past infidelities and endorse him for the Jan. 3 caucuses.
The Family Leader, one of the state's most influential evangelical groups, is in intense debate about whether to back Gingrich, a front-runner in the contest to choose the Republican to face Democratic President Barack Obama in November.
One influential Christian conservative in Iowa said group leader Bob Vander Plaats, a respected force in Iowa Republican politics, is facing opposition from members for his support for Gingrich.
"Bob wants to go with Gingrich," the source said. "Too many supporters around him think that's utter madness. So they may go their separate ways."
Vander Plaats has publicly said he has not made a decision, but Gingrich lent significant financial backing to a 2010 effort in Iowa, led by the group leader, which wound up with three Iowa Supreme Court justices voted off the court in a fight over gay marriage.
The group failed to resolve their differences over Gingrich at a meeting Friday and will meet again Monday. Julie Summa, a spokeswoman for The Family Leader, said that an announcement on an endorsement would come early in the week.
Backing from The Family Leader could help propel a candidate to the top of the field in Iowa, which holds the first nominating contest for the 2012 presidential election, although time is running out. Evangelicals lifted former Arkansas Governor Mike Huckabee to a surprise 9-point win in the state in 2008.
While some leaders in the religious movement are loyal to Gingrich as someone who has long fought for conservative causes, many evangelical Christians are uneasy about Gingrich's marital past. The problem may also dog him in other early voting states where conservatives are strong, like South Carolina.
Gingrich has been divorced twice and admitted to cheating on his first two wives, including while he led the charge to impeach former President Bill Clinton for the Monica Lewinsky affair. He has led most recent polling in Iowa ahead of the caucuses, but opponents Ron Paul and Mitt Romney are not far behind and an endorsement could make all the difference.
A source said The Family Leader is tending toward endorsing Rick Santorum or Rick Perry, both of whom have strong conservative credentials and often talk of family values. Vander Plaats may end up personally endorsing the former House speaker if that happens, the source said. Vander Plaats has not been available for comment for several days.
Six of every 10 Iowans who participated in the 2008 Republican contest said they were born-again or evangelical Christians, making them potential kingmakers if they settle on one candidate.
Cary Gordon, pastor of the World Outreach Church in Sioux City, has endorsed Santorum for the nomination and says Gingrich's marital troubles were part of that decision.
"Absolutely," said Gordon, who is not a member of Family Leader. "There's no way I can trust him."
"There's a lot of hesitation about Newt Gingrich," he said. "There's no more sacred commitment to another human being than marriage."
Steve Deace, a national conservative radio host based in Iowa, said Vander Plaats respects Gingrich's "boldness" when he helped the Family Leader group bankroll the ousting of Iowa state Supreme Court justices who ruled in favor of gay marriage.
Deace said Gingrich "ought to get more credit" for his help in defeating the justices who essentially legalized gay marriage in Iowa.
Other pastors and evangelical leaders view Gingrich skeptically.
"The number of social conservatives who don't like Newt Gingrich is small," he said. "But the number of social conservatives who don't trust Newt Gingrich is big. Conservatives are fired up because he's been championing their issues in debates but he's got lots of baggage from the past."
Gingrich has converted to Catholicism, influenced by his third wife Callista, and says he has asked God's forgiveness for his adultery.
Santorum, a longtime champion of socially conservative causes who is trailing in the polls, took a shot at Gingrich on Wednesday at the premier of the anti-abortion movie "The Gift of Life."
After Gingrich said in a statement to The Family Leader that he believes life begins at conception, Santorum used his time at the premier, in front of the Christian conservative audience, to paint Gingrich as not a strong anti-abortionist.
"I have some problems with some of the folks, you know, running for office these days when they say, 'I believe life begins at conception,'" Santorum said. "It's like (saying), 'I believe the sun rises.'"
Michele Bachmann, another contender for the endorsement and a friend to social conservatives, has the backing of a group of pastors and former State Representative Danny Carroll who traveled the state for three days last week, urging Christians conservatives to support Bachmann.
Until about a year ago, Carroll served on The Family Leader's board of directors. He is now the group's lobbyist at the Iowa statehouse.
"We come here this morning to ask Christians across Iowa to support Michele Bachmann," Carroll said during a statehouse news conference last week.
"We have determined that Michele Bachmann is Biblically qualified to be the president, to be a leader. She is capable. She is trustworthy. She fears God and she hates dishonest gain." (Additional reporting by Kay Henderson; Editing by Vicki Allen)