Gay marriage has lost in every single state in which it has been put to a popular vote. Come Election Day, gay-rights supporters are hoping to make Maine the exception.

In a referendum that is being closely watched around the country and has drawn millions in out-of-state dollars, Maine voters will decide Tuesday whether to repeal a state law that would allow same-sex couples to marry.

If it is repealed, it will be another major defeat for the gay-rights movement, which saw voters in California put a stop to same-sex weddings there last year. A loss in Maine would be especially heartbreaking, given the way New England has been the region of the country most receptive to gay marriage.

The polls have been difficult to interpret. But both sides say the contest will be extremely close and will hinge on turnout, particularly among the 18-to-25-year-olds who went to the polls in great numbers last year to elect President Barack Obama.

"There's a knot in my stomach," said Steve Ryan of Buxton, who operates a property management business with his partner of 34 years, Jim Bishop. "We're very encouraged, and we're very worried at the same time."

Gay-marriage supporters have framed the issue as a matter of equality for all families, straight or gay. Opponents say that allowing same-sex couples to wed would be a dangerous social experiment and that Maine's domestic registry law could simply be bolstered to give gays additional legal rights.

"The stakes are very high for both sides. The gay marriage community has never won at the ballot box before on a straight up-or-down vote," said Frank Schubert, who coordinated the campaign to override California's highest court and repeal gay marriage there.

Over the past five years, 26 states have passed constitutional amendments limiting marriage to a man and a woman.

The Maine law was passed by the Legislature last spring but never went into effect because of a petition drive by opponents. Five other states have legalized gay marriage: Connecticut, Massachusetts, New Hampshire and Vermont _ all in New England _ and Iowa. All five of them did it by way of court or legislative action, not referendums.

"California was just a dress rehearsal for Maine," said Christian Potholm, a political science professor at Bowdoin College in Brunswick.

In related action Tuesday, voters in Washington state will decide whether to expand their domestic partnership law, and people in Kalamazoo, Mich., will consider whether to prohibit discrimination against gays.

In Portland, boisterous supporters of gay marriage _ many of them students _ far outnumbered the other side at the University of Southern Maine debate last week. Continued...