A proposed constitutional amendment prohibiting gay marriage divided a legislative panel precisely along party lines Friday, setting up a rough road for the bill in the Democratically controlled House, where it must win approval from two-thirds of members.

Six Democrats on the Legislature’s Judiciary Committee opposed the bill, sponsored by Rep. Brian Duprey, R-Hampden, calling it a “wedge issue” motivated primarily by politics.

“I understand how it might energize fundamentalist voters but I’ve yet to hear what public policy change will occur as a result of this bill,” Rep. Sean Faircloth, D-Bangor, said after the vote, which concluded an hour-long debate in Augusta over the bill’s necessity considering Maine already has a state law prohibiting same-sex marriage.

As of Friday afternoon the committee’s two remaining Democrats had not cast their votes, but were expected to oppose the measure.

Many conservatives favor a constitutional ban, which is considered more difficult to overturn.

On Friday, the committee’s five Republicans supported Duprey’s bill after removing a sentence designed to prohibit any domestic partnership resembling marriage such as civil unions.

“I can support now and in the future that marriage should be limited to a man and a woman,” said Sen. David Hastings, R-Fryeburg, arguing that the pared-down amendment would not jeopardize existing state laws allowing unmarried partners some benefits of marriage.

After the vote, Duprey said he welcomed the change, believing it would bolster the bill’s chances in the House, where Democrats hold a slim majority.

“I’ve already had a few Democrats tell me they could support it [without the civil union ban,]” Duprey said. “It’s going to be a really close vote.”

To amend the Maine Constitution, as Duprey’s bill intends, two-thirds of lawmakers in both the House and Senate must approve the measure for statewide referendum. A majority of Maine voters then must favor the change.

While the Hampden Republican might be hopeful of swaying some from across the aisle, Democratic leaders predicted little dissention within the party.

“I can’t tell you every single Democrat will vote against it, but I would say most of our caucus believes [a constitutional amendment] is unnecessary,” said House Majority Leader Glenn Cummings, D-Portland.

Last year, Duprey submitted a similar measure, which was defeated in both houses on a largely party-line vote.

Maine is one of 37 states that prohibit gay marriage in state statute. The stricter constitutional bans are in effect in 17 states – mostly in the South and Midwest.

Voters in 11 of those states approved constitutional changes in the November 2004 elections. Some pundits credit those ballot measures – particularly Ohio’s – with mobilizing conservative voters and delivering the election to Republican President George W. Bush.

While debate over same-sex marriage extends nationwide, during the past year it has centered on Massachusetts, the only state that officially sanctions such unions.

That distinction came as the result of a 2003 court decision finding unconstitutional the state’s practice of denying marriage licenses to gay couples.

There have been court challenges of gay marriage bans in other states. Earlier this month, a federal judge struck down Nebraska’s constitutional prohibition, ruling it was too broad.