The president of the US National Association of Evangelicals resigned yesterday after being accused of having a sexual relationship with a male escort.
A screen grab from Mr Haggard's website
Ted Haggard, who has had regular talks with the White House and vocally opposes gay marriage, denied the accusation.
He has also temporarily stepped down as senior pastor of the New Life Church in Colorado Springs.
"I've never had a gay relationship with anyone," Mr Haggard said in a television interview. "I'm steady with my wife. I'm faithful to my wife."
The church statement quoted Mr Haggard as saying he could "not continue to minister under the cloud created by the accusations."
"I am voluntarily stepping aside from leadership so that the overseer process can be allowed to proceed with integrity. I hope to be able to discuss this matter in more detail at a later date," the church statement quoted Mr Haggard as saying.
Mike Jones, who said he was a male escort, said on Wednesday he had had a three-year sexual "business relationship" with Mr Haggard.
Mr Haggard, who is often credited with rallying conservative Christians behind President Bush for his 2004 re-election, talks to Mr Bush or his advisers every Monday, Harper's Magazinereported last year.
Mr Haggard supports a proposed amendment to the Colorado constitution that defines marriage as between one man and one woman. Colorado voters will decide on that issue next week when they vote in the congressional elections.
Evangelical Christians have been a key base of support for Mr Bush and the Republican Party. A father of five, Mr Haggard has long been a leading figure among conservative US evangelical Christians.
Timeincluded him in its list of the "25 Most Influential Evangelicals in America." Harper's, an influential liberal periodical, described New Life last year as "America's most powerful megachurch".