Updated

Gay-rights activists could score victory at the ballot box in Maine on Tuesday, as voters head to the polls to decide whether to repeal a law that would allow same-sex marriage.

The law was passed by the Legislature and signed by Democratic Gov. John Baldacci last May, but has never taken effect. If voters uphold the law, Maine will become the first state to endorse same-sex marriage by popular referendum, energizing activists nationwide and deflating a long-standing conservative argument that gay marriage lacks popular support.

Conversely, a repeal -- in New England, the corner of the country most receptive to same-sex marriage -- would be a jolting setback for the gay-rights movement and mark the first time voters overturned a gay-marriage law enacted by a legislature. When Californians voters rejected gay marriage a year ago, it was in response to a court ruling, not legislation.

Apart from Maine, five states have legalized same-sex marriage -- Iowa, Connecticut, Massachusetts, Vermont and New Hampshire. But all did so via legislation or court rulings, not through a popular vote. By contrast, constitutional amendments banning gay marriage have been approved in all 30 states where they have reached the ballot.

Gay rights is also on the ballot Tuesday in Washington state, where voters will decide whether to uphold or overturn a recently expanded domestic partnership law that gives same-sex couples the same state-granted rights as heterosexual married couples.

After lawmakers passed the state's first domestic partnership bill in 2007, and then expanded it a year later, they completed the package with the so-called "everything but marriage" bill that was signed into law by Gov. Chris Gregoire earlier this year.

Referendum 71 asks voters to "approve" or "reject" the final expansion to the state's domestic partnership law, which grants registered domestic partners additional state-granted rights currently given only to married couples. Under state law, heterosexual seniors also can register as domestic partners.

"The eyes of the nation will be on Maine," Rea Carey, executive director of the National Gay and Lesbian Task Force, told the Associated Press. "The stakes are high, but so is our hope that Maine will remain among the growing number of states that extend the essential security and legal protections of marriage to all loving, committed couples."

Brian Brown of the New Jersey-based National Organization of Marriage, which has contributed $1.5 million to the repeal campaign, agreed the election is critical for both sides.

He took heart in polls showing a close race, saying polling in other states that voted on the issue tended to underestimate the eventual opposition to same-sex marriage.

"New England is the one area where it's much tougher ground for us than other states," Brown told the Associated Press. "The fact that in a state like Maine we're polling relatively even shows the depth of support for saying marriage is between a man and a woman."

Both campaigns have attracted volunteers and hefty financial support from out of state, but the financial advantage went to the side defending same-sex marriage, Protect Maine Equality. It raised $4 million, compared with $2.5 million collected by Stand for Marriage Maine, which forced the repeal vote through a petition drive.

The Roman Catholic Diocese of Portland coordinated $550,000 in contributions to the repeal campaign and has criticized Baldacci, a Catholic and former altar boy, for signing the marriage law.

Gay-marriage opponents have stressed the theme -- disputed by their rivals -- that gay marriage will be taught in schools if the law is allowed to stand. A Stand For Marriage radio ad Monday focused on an attempt to strip the state license from a high school counselor who spoke out against gay marriage in a television commercial.

The Associated Press contributed to this report.  

Brian Brown of the New Jersey-based National Organization of Marriage, which has contributed $1.5 million to the repeal campaign, agreed the election is critical for both sides.

He took heart in polls showing a close race, saying polling in other states that voted on the issue tended to underestimate the eventual opposition to same-sex marriage.

"New England is the one area where it's much tougher ground for us than other states," Brown told the Associated Press. "The fact that in a state like Maine we're polling relatively even shows the depth of support for saying marriage is between a man and a woman."

Both campaigns have attracted volunteers and hefty financial support from out of state, but the financial advantage went to the side defending same-sex marriage, Protect Maine Equality. It raised $4 million, compared with $2.5 million collected by Stand for Marriage Maine, which forced the repeal vote through a petition drive.

The Roman Catholic Diocese of Portland coordinated $550,000 in contributions to the repeal campaign and has criticized Baldacci, a Catholic and former altar boy, for signing the marriage law.

Gay-marriage opponents have stressed the theme -- disputed by their rivals -- that gay marriage will be taught in schools if the law is allowed to stand. A Stand For Marriage radio ad Monday focused on an attempt to strip the state license from a high school counselor who spoke out against gay marriage in a television commercial.

The Associated Press contributed to this report.