* Annual "Pulpit Freedom Sunday" gains in popularity
* Pastors' campaign could have influence in swing states
* Past events tended to be dominated by conservatives
CHARLOTTE, N.C. Oct 7 (Reuters) - Baptist Pastor Mark Harris stood before his flock in North Carolina on Sunday and joined hundreds of other U.S. religious leaders in deliberately breaking the law in an election-year campaign that tests the role of churches in politics.
By publicly backing candidates for political office from the pulpit, Harris and nearly 1,500 other preachers at services across the United States were flouting a law they see as an incursion on freedom of religion and speech.
Under the U.S. tax code, non-profit organizations such as churches may express views on any issue, but they jeopardize their favorable tax-exempt status if they speak for or against any political candidate.
"Pulpit Freedom Sunday" has been staged annually since 2008 by a group called the Alliance Defending Freedom. Its aim is to provoke a challenge from the U.S. Internal Revenue Service in order to file a lawsuit and have its argument out in court.
The event has grown steadily in size, but the IRS has yet to respond - even though the pastors tape their sermons and mail them to the agency.
Now in an election year, where a few swing states - including North Carolina - will be crucial, political analysts say pastors campaigning from the pulpit could have an impact.
Critics say the movement threatens the U.S. constitutional principle of separation of church and state and makes pastors look like political operatives rather than neutral spiritual leaders.
"When the church further divides the country, where's the win in that?" asked Reverend C. Welton Gaddy, president of the Interfaith Alliance, and an opponent of "Pulpit Freedom Sunday."
In his sermon at First Baptist Church in Charlotte, North Carolina, Harris endorsed a Republican candidate for the state's Supreme Court, but did not specifically takes sides in the Nov. 6 contest for the White House between Democratic President Barack Obama and Republican challenger Mitt Romney.
"I don't feel I'm breaking the law," Harris said before addressing a congregation of almost 1,000. "I am speaking as a pastor and as a citizen of the United States where we have that freedom of speech."
EVENT'S POPULARITY GROWS
Erik Stanley, senior legal counsel of the Alliance Defending Freedom, said the group was not pushing any particular political agenda and participants came from both conservative and liberal churches.
However, the event in past years has tended to be dominated by evangelical fundamentalist churches and conservative causes such as opposition to abortion and gay-marriage.
It has grown steadily in size, with just 33 pastors taking part in 2008, rising to 539 last year and to a record 1,477 this year.
It is not entirely clear why the IRS has stayed silent and the agency did not respond to a request for comment.
Stanley said that if the IRS continued to ignore the speeches, it could become clear it was not enforcing the ban and hand preachers the de facto right to do as they wish from the pulpit.
IRS LOST KEY CASE IN 2009
Marcus Owens, a partner with law firm Caplin & Drysdale and former head of the IRS division that oversees tax exempt organizations, cited a 2009 case as a turning point.
In that case, the agency took action against James Hammond, pastor of the Living Word Christian Center in Brooklyn Park, Minnesota, after he endorsed Republican Michele Bachmann for Congress.
The move led to a challenge of the IRS' audit procedure for churches, which the agency lost, and since then there have been no publicly known examples of it taking action against churches.
In its latest annual report, the IRS indicated it planned to examine allegations of political intervention by pastors.
But experts who spoke to Reuters said they do not expect the agency to move against Pulpit Freedom Sunday this year, chiefly because of the absence of a new audit procedure for churches.
"If the IRS wanted to get serious about this, there are already plenty of blatant violations they could pursue," said Rob Boston of Americans United for Separation of Church and State, a Washington-based group that monitors and informs the IRS about tax-code violations.
BIG SCREEN, POLITICS
Pacing across the church stage and backed by large screens showing closeups of his face, Harris argued in his sermon that issues such as the sanctity of life, marriage, religious freedom and the national debt mattered "to the judgment hand of God."
"The American politician must hear you. You, sir and ma'am, are responsible for the governing of this nation today," he declared as his congregation rose in a standing ovation.
"As a follower of Jesus Christ, I will not vote for a candidate that violates the principles of God on the issues I've discussed," he said, before going on to endorse Paul Martin Newby, Republican candidate for the state Supreme Court.
Churchgoer Dixie Martin said some in the congregation were uncomfortable with the overt political talk, but she added: "We needed to hear it."
A registered Democrat, Martin said she would be voting Republican this year and was glad to learn more about Newby in a race she had not been following.
Obama won North Carolina by just 14,000 votes in 2008. Recent polls show him now in a dead heat there with Romney.
Though the state has changed over the years, with new population inflows from other parts of the country, it retains a strong churchgoing base.
This means sermons just before elections could be critical, strategist from both political parties agreed.
Paul Shumacker, a long-time North Carolina consultant to Republican candidates, said regular churchgoers tended to be engaged in their communities and formed a strong voter base.
In a race as close as the one between Obama and Romney, "anything that works to build intensity becomes absolutely critical," he said.
A July poll by the Pew Forum on Religion and Public Life found 66 percent of Americans believe churches or other houses of worship should not endorse political candidates. That figure was only 56 percent among white evangelical Protestants. It was 69 percent among Catholics.
Jason Husser, a political science professor at North Carolina's Elon University, said evangelical pastors may be more comfortable speaking out on politics than leaders of other faiths because their congregations tended to be more uniformly conservative and Republican.