An outspoken and polarizing voice in conservative Christian politics resigned effective Thursday from the National Association of Evangelicals after a radio interview in which he voiced support for same-sex civil unions and said he is "shifting" on gay marriage.

The Rev. Richard Cizik's comments — made on a Dec. 2 "Fresh Air" broadcast on National Public Radio — triggered an uproar that led to his stepping down as NAE vice president of governmental affairs.

A fixture in Washington for nearly three decades, Cizik has played a key role in bringing evangelical Christian concerns to the political table. But in recent years, he earned enemies in the movement for pushing to broaden the evangelical agenda.

His strongest focus was on "creation care," arguing that evangelicals have a biblical responsibility to the environment that includes combatting global warming.

The Rev. Leith Anderson, a Minneapolis-area pastor who serves as NAE president, said Thursday the group is not backing away from its environmental stances. Cizik's resignation was necessary, he said, because some of his answers in the radio interview did not reflect NAE values and convictions.

"Any organizations that speak to controversial issues are going to have critics," Anderson said. "What was different this time was our individuals and organizations felt there was a loss of credibility for him clearly espousing our positions and values. When you lose that, it's very difficult to re-establish."

Cizik did not immediately respond to requests for comment Thursday. The NAE said in a statement that Cizik had expressed regret, apologized and "affirmed our values."

The NAE is an umbrella group for tens of thousands of churches and organizations.

Anderson said a "combination of things" Cizik said in the interview led to his downfall, including this comment on gay marriage: "I'm shifting, I have to admit. In other words, I would willingly say I believe in civil unions. I don't officially support redefining marriage from its traditional definition, I don't think."

Coming off the passage last month of amendments barring gay marriage in three states, some evangelicals took that as a slap in the face, said David Neff, editor of Christianity Today magazine and a member of the NAE executive committee.

"He seemed to be abandoning the one thing where evangelical activists felt they had actually made a difference this time around," Neff said.

Anderson said others were troubled that Cizik discussed nuclear weapons as a foreign-policy issue when he could have focused on religious freedom or human trafficking — issues he has championed.

Still others were disappointed Cizik volunteered that he voted for Barack Obama in the Democratic primaries, Anderson said. Cizik also hinted that he voted for Obama in November.

"I don't want anybody to think, because I'm the lobbyist in chief for the National Association of Evangelicals, that because I voted one way or the other, I can't represent their concerns," Cizik said. "So, I believe I can. I happen to think in the primary it was the best choice. People disagreed."

Anderson said the problem wasn't necessarily that Cizik backed Obama, but that he answered the question at all as a representative of a group that remains neutral on candidates.

"He wishes he could do the interview again," Anderson said. "I wish he could do the interview again. As we discussed it, he realized how difficult this would be and resignation was probably best for him and NAE."

One of Cizik's fiercest critics has been Focus on the Family, the Colorado Springs, Colo.-based evangelical group founded by James Dobson. Last year, Dobson and other Christian conservatives unsuccessfully pressured the NAE to silence Cizik about global warming.

"It was time for him to go," Tom Minnery, a Focus on the Family senior vice president, said Thursday. "He no longer represents the view of evangelicalism. He has not represented those views for some time."

More tradition-minded evangelical activists believe an environmental focus distracts attention from abortion and gay marriage, or they don't believe in global warming or that human activity causes it.