With the 2012 Republican presidential field slowly taking shape, potential candidates are barnstorming early primary states, with an eye on a group that will prove decisive in picking the eventual GOP nominee: evangelicals.

Likely candidates have met with preachers, conservative Christians and religious leaning home-schoolers in South Carolina, New Hampshire and Iowa, where winning the evangelical vote is tantamount to winning the caucus.

On Saturday, they appeared on “Rediscover God in America,” a day-long broadcast that aired in more than 200 churches across the country.

Those congregations included Leesburg Church of the Nazarene, where about 25 parishioners gathered in plush pews in the sanctuary to take notes and hear from evangelical leaders and likely White House candidates vying for an edge with a group that nationally makes up about 40 percent of the Republican Party, according to polls.

Mike Huckabee, former governor of Arkansas and a Baptist minister, was an early speaker, quoting from the New Testament and saying that it was up to people of faith to reclaim America.

“My dear friends, we face a spiritual war in this country, and the idea of this wonderful nation built on a Judeo-Christian principle that we are accountable and answerable to a holy God is on the line,” Huckabee said.

“We will either give it to the next generation as a great gift of grace and freedom, or we will be the ones who lose it, and someone will have to come later and try to save it, revive it and give it back.”

Mississippi Gov. Haley Barbour, who has low national name recognition, outlined a tough approach to abortion, signaling that he wouldn’t cede any ground on social issues, as others in his party have suggested.

“We’re doing everything that we can to stop abortion in our state,” Barbour said at the pastor’s conference, which was taped in Iowa Thursday and Friday. “And if I run for president, I will come to office with that attitude, which is about 180 degrees different from the person we have in there now.”

Former House speaker Newt Gingrich said that on Day One, the next president should be ready to sign a raft of executive orders.

“The very first executive order should be to abolish all the czars in the first act,” he said, a line which drew applause. “The second executive order ought to be to reinstate . . . policy that no American money pays for abortion anywhere in the world.”

Gingrich, who had a 61 percent approval rating among evangelical Republicans in a recent Washington Post poll, was well received, with churchgoers picking up copies of his DVD. But some weren’t sure that his values matched up with their beliefs.

“I think as a historian and as a very educated man, he would make a great president,” said Elizabeth Munsey, 51, a building manager. “I’m just not sure of his moral standards.”

Rep. Michele Bachmann (Minn.) is also scheduled to speak.

Parishioners said they were listening closely to where politicians stand on the issues, particularly marriage and abortion.

“Huckabee would get my vote if he runs because he has a lot of good ideas,” said Daniel Wright, a 49-year-old truck driver who said he watches “Huckabee,” the former governor’s show on Fox News, every Saturday. “He goes by what the Bible says, and we need someone strong that way.”

Huckabee, who finished second in the 2008 GOP primary, retains residual support among evangelicals, and a Washington Post/ABC News poll shows him leading all other potential candidates with a favorability rating of 76 percent among white evangelical Republicans and GOP-leaning independents.

Evangelicals, though backing Republicans over Democrats by margins as high as 4 to 1, can be picky voters from state to state and from candidate to candidate. In 2000, according to former George W. Bush political strategist Karl Rove, as many as 4 million chose to sit on their hands rather than pull the lever for Bush after revelations about his drunken-driving arrest came out in the days before the November election.

Four years later, evangelicals showed up in greater numbers for Bush, galvanized by amendments to ban same-sex marriage on 11 state ballots. But that fervor went south by the end of Bush’s term over the Iraq war and what some evangelicals saw as Bush’s paltry domestic accomplishments over two terms.

In 2008, Huckabee ran strongly in Iowa but failed to solidify evangelical support across the board, losing the GOP nomination to Sen. John McCain (Ariz.), who ended up getting 74 percent of the white evangelical vote to President Obama’s 24 percent.

Yet since then, high unemployment, a ballooning deficit and the emergence of the fiscally driven tea party have led some top Republicans, such as Indiana Gov. Mitch Daniels, to argue that the GOP should de-emphasize social issues such as same-sex marriage and abortion, and instead focus on the economy.

Warren Smith, associate publisher at World Magazine, a Christian biweekly, said the lesson of the 2000 race for candidates seeking evangelical support in 2012 is simple:

“If you want the socially conservative evangelical voter to turn out for you, you had better stand up for us,” he said. “Evangelicals aren’t interested in declaring a truce on social issues, and they are energized and they are going to be very active in this cycle.”

In the 2010 midterms, evangelical support for the GOP surged by seven percentage points over the 2006 midterms, with 77 percent of white evangelical Christians backing House Republicans vs. 19 percent for Democrats.

Much of the focus of activity is in early primary states such as Iowa, where Saturday’s Web event was taped and where evangelicals have played kingmaker in Republican caucuses; 60 percent of Iowa caucusgoers are evangelicals.

But Republicans will also need big turnout among Christian conservatives in states such as Virginia, which went blue in 2008 and where nearly 33 percent of the population is white evangelicals, to win. Nazarene’s senior pastor, Gary Smith, said he wants his parishioners to start tuning in now as well to hear where potential candidates from both parties stand on the issues.

“I want them to understand the biblical world view and get some historical perspective,” he said. “And I want them to be stirred in their hearts to do something politically.”