The House yesterday rejected a constitutional amendment to ban gay marriage in an election-year vote aimed at appeasing Christian conservatives, a key part of the GOP base.

The vote was part of the GOP leadership’s American Values Agenda, 10 legislative items coveted by conservatives and questioned by some centrist Republicans, that leaders hope to address before the November election.

The amendment, which was introduced by Rep. Marilyn Musgrave (R-Colo.), lost, 236-187, falling 47 votes shy of the two-thirds majority necessary to approve a constitutional amendment.

Twenty-seven predominantly centrist Republicans opposed the measure. They included two members of the Speaker’s leadership team: Republican Conference Chairwoman Deborah Pryce (R-Ohio) and Rules Committee Chairman David Dreier (R-Calif.).

Despite yesterday’s failed attempt, the bill picked up eight votes from September 2004, when 227 lawmakers supported the measure and 186 rejected it after House leaders brought a previous version to the floor within months of the last election.

Rep. Jim Gibbons (Nev.), who is running for governor, was the only Republican who voted no in 2004 and yes this year.

In a statement, Gibbons said he changed his vote because Congress has failed to approve a measure he supports to strip courts at every level from hearing cases that that deal with same-sex marriage.

“I had hoped it wouldn’t come to this, but since Congress refuses to act, the only option available to me is to support the passage of the Marriage Protection Amendment,” Gibbons said. “This is the only way to ensure that marriage has the protection it needs from activist federal judges.”

The author of the court-stripping bill, Rep. John Hostettler (R-Ind.), a staunch Christian conservative, opposed the marriage amendment yesterday and in 2004.

No Democrat switched his or her vote.

Politically vulnerable House Democrats serving in their first term split on the Musgrave bill. Reps. John Barrow (D-Ga.) and Charlie Melancon (D-La.) voted yes, while Reps. Melissa Bean (D-Ill.) and John Salazar (D-Colo.) rejected it.

Freshman Rep. Dan Lipinski (D-Ill.), who is not facing a difficult race this fall, voted present.

The amendment, just like its predecessor, sought to define marriage as existing only between a man and a woman and was a priority for many family-values groups in and out of the Beltway.

This was the third vote in the American Values Agenda, which House Speaker Dennis Hastert (R-Ill.) introduced last month to minimal fanfare. After the amendment fell short yesterday, the Speaker criticized Democrats who opposed the measure and said a majority of Americans support the ban.

“Be assured that this issue is not over and that we will continue to send a message to the American people that preserving and protecting marriage is a priority,” Hastert said in a statement.

House Democrats condemned the marriage vote as a partisan political maneuver after the Senate rejected a similar amendment on a procedural vote last month that prevented leaders from bringing it to a vote.

President Bush campaigned heavily on social values during his reelection bid in 2004. Karl Rove, his principal political adviser, spent years catering to evangelical Christians in the hopes that they would go to the polls to support the president, but one GOP lawmaker suggested last week that congressional leaders were less deliberate in their own appeal to those voters because they are not always loyal Republicans.

“These are single-issue voters, not Republicans,” the lawmaker said on the condition of anonymity.

Some of the Republicans who opposed the amendment were centrist lawmakers locked in tough reelection campaigns, like Reps. Mike Fitzpatrick (Pa.), Jim Gerlach (Pa.) and Rob Simmons (Conn.).

The Constitution has only been amended 27 times since it was ratified. For yesterday’s amendment to become law, both chambers would have to approve it with a two-thirds majority and then 38 states would have to support its adoption.

The House previously approved bills to enhance enforcement mechanisms on Internet gambling sites and to protect the Pledge of Allegiance from court challenges as two other parts of the American Values Agenda.