Vander Plaats, president of The Family Leader, greets Iowa Senate candidate Ernst following her speech at the Family Leadership Summit in Ames Thomson Reuters SPRINGDALE Ark. (Reuters) - If Republicans win control of the Senate in the midterm elections they should say a prayer of thanks for Christian conservatives.

Although they get little attention from candidates, white evangelical Christian voters are likely to be fundamental to any Republican victories in the key Senate races, especially in the South.

Reuters/Ipsos polling data shows evangelicals are more enthusiastic than the general population about the midterms.

The religious right's influence may be much reduced since the days of Moral Majority leader Jerry Falwell's alliances with Republican presidents.

But Christian conservatives will probably vote in greater numbers on Nov. 4 than others, giving them an outsized say in who runs Congress. Forty-nine percent of evangelicals say they have a great deal of interest or quite a bit of interest in news about the elections, compared to 38 percent of non-evangelicals.

"It strongly shows that the evangelical population is very engaged, very interested in what's happening and much easier to turn out for an election than the population as a whole," said Ipsos pollster Chris Jackson.

Almost 40 percent of Republicans said they were born-again or evangelical Christians, according to the online survey.

The party loyalty is striking given that Republican candidates have largely avoided evangelicals' pet topics like opposition to abortion and gay marriage for fear of alienating moderate voters in tight U.S. Senate races.

In one of the few Senate contests where social issues have taken center stage, Colorado Republican Cory Gardner distanced himself from his earlier support for "personhood" bills backed by evangelicals. Such bills would define fetuses as people, and could lead to abortion and some forms of birth control being declared as murder.

In Iowa, Republican Senate hopeful Joni Ernst seemingly softened her strong opposition to abortion when she suggested in a debate this month that there could be exceptions if the mother's life is at risk.

The Supreme Court's decision earlier this month to allow gay marriages by rejecting appeals from five states seeking to ban them was a landmark in longrunning culture wars, but it passed without much fuss on midterm campaign trails.

"The candidates, certainly the Democratic candidates, are not talking about these issues and in most cases the Republican candidates aren't talking about these issues, so we are going to talk about them," said veteran conservative activist Ralph Reed.

His Faith and Freedom Coalition has launched what Reed said is its "most muscular" turnout operation yet. It includes making 10 million phone calls to potential voters and an aggressive ad campaign of online videos.

The idea is to ensure enough evangelical turnout to swing Senate races in states such as Arkansas, Georgia, Louisiana, Iowa, Colorado, North Carolina and Kentucky, where polls show the average gap between the top candidates is in the low single digits. Republicans need a net gain of six seats to win the Senate.

In some ways, Reed is preaching to the choir. White evangelicals have long had a high rate of midterm voting and more than three-quarters of them backed Republican Mitt Romney against President Barack Obama in the 2012 presidential election.

"Evangelicals have in fact become one of the core constituencies in the Republican Party. Because they see themselves that way, we see their willingness to vote consistently Republican, even though you could point to a number of issues where the Republican-led House (of Representatives)really hasn’t moved much on their agenda," said Robert P. Jones of the Public Religion Research Institute polling group.

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Chad Connelly, the Republican National Committee's pointman for faith voters, said evangelical voters are motivated by worry about the economy and mistrust of Obama, adding, "it's too much of a cliche," to think they care mostly about social policy.

Conservative Christians at a Baptist church in Springdale, Arkansas, had a long list of issues that matter to them.

"Where a candidate stands on marriage, immigration, the economy: it's all important. I don't think Obama's doing a good job with terrorism either," said Mary Baker, a retiree.

Nevertheless, the stress was on social issues when she and some 20 others at the church watched a national webcast by evangelical leaders who urged the faithful to support "Biblical" values at polling booths.

While the hosts did not specifically ask people to vote Republican, they told Christians to back candidates who hold conservative positions on abortion, freedom of religious expression, and same-sex marriage.

The congregation mostly agreed. Some voiced disappointment that Republicans failed to choose a Christian conservative as presidential nominee at the last two elections.

"We end up with a crippled duck every time," said Charles Fast, 70, a former policeman.

In the Arkansas Senate race, a Fox News poll this month gave Republican Tom Cotton a 34-point lead over Democratic Sen. Mark Pryor among white, born-again Christian voters.

Even if their votes sway the next Congress, Christian conservatives are going through a difficult period of soul searching over falling church attendance and America's shifting attitudes toward gay rights.

"When same-sex marriages are being conducted in Oklahoma, the culture has shifted dramatically. We have to be honest about that," said Russell Moore, the most prominent leader of the Southern Baptist Convention.

White Protestants are shrinking as a proportion of the U.S. population. And Moore's denomination, the largest Protestant group in America, has lost membership every year since 2007 as young people drift away. An internal survey found a quarter of Southern Baptist churches that reported statistics did not baptize a single person in 2012.

(Editing by Frances Kerry)