Sen. Lawrence Bliss, D- South Portland, right, an openly gay legislator, is congratulated by fellow lawmakers May 6 in the Senate chamber after they voted and gave final approval to a gay rights marriage bill at the State House in Augusta, Maine. Senators are, from left, Joseph Perry, D-Bangor, Dennis Damon, D-Trenton, and Bruce Bryant, D-Dixfield. In November, Maine voters will become the first in any state with the chance to repeal or uphold a law passed by their legislature legalizing same-sex marriage.

Portland, Maine ? For an off-year election, in a state only rarely in the national political spotlight, an upcoming referendum on same-sex marriage has dramatic potential to make history and to roil emotions from coast to coast.

On Nov. 3, Maine voters will become the first in any state with the chance to repeal or uphold a law passed by their Legislature and signed by their governor, legalizing same-sex marriage. The outcome is considered too close to call, and the race is galvanizing activists on both sides of the issue across the country.

The ballot measure, Question One, results from Maine’s provision for a “people’s veto” — any newly passed law can be subject to repeal by voters if enough valid signatures are obtained to trigger a referendum.

“The stakes are very high in Maine, no question about it,” said Frank Schubert, who was hired by gay-marriage opponents in Maine as their top strategist after he coordinated the Proposition 8 campaign last year in California that repealed court-ordered gay marriage there.

Though five other states have legalized same-sex marriage, including four of Maine’s New England neighbors, none has done it with the affirmation of a popular vote. Maine could be the first — a prospect that worries Schubert and his allies.

“It would be first time gay marriage advocates would be able to convince the public to be on their side,” he said. “It would add to their attempt to convince people that it’s inevitable they will win, that it’s just a matter of time.”

Supporters of same-sex marriage, in Maine and elsewhere, are cautiously hopeful of a landmark victory that they believe would have impact in other states, including California. But they acknowledge that defeat — by an electorate known for its independence and moderation — would be crushing.

“If we lose, it will be a day of tremendous grief,” said Judy Chamberlain, who along with her partner of 30 years, Karen Marlin, has been working in the campaign to uphold the marriage law.

Chamberlain, 57, and Marlin, 62, who hope to wed in their church in Brunswick, got engaged in May when the state Senate approved the marriage bill. Marlin replied to Chamberlain’s proposal by text message: “You bet.”

Their 17-year daughter, Nena, adopted from Russia as a toddler, hopes her mothers get the election result they’re working for.

“It would be cool for them,” she said. “They’ve been wanting it so long.”

Among the lawmakers backing the marriage bill was Sen. Larry Bliss, an openly gay Democrat who moved many colleagues with personal stories of raising a family as half of a same-sex couple. Initially, Bliss felt the bill was premature, but changed his mind when his longtime partner quit his job and needed to get on Bliss’s health insurance.

“If he’d been my spouse, it would have been easy,” Bliss said. “Instead the process was appallingly humiliating.”

Many Mainers were surprised by the decision of Democratic Gov. John Baldacci, a Roman Catholic, to sign the bill swiftly on May 6 despite having voiced doubts about same-sex marriage.

The spiritual leader of Maine’s 200,000 Catholics, Portland Bishop Richard Malone, said he was “deeply disappointed” in Baldacci and legislative leaders, and called same-sex marriage “a dangerous sociological experiment.” Catholic churches statewide have taken collections to aid the repeal effort.

Baldacci, a former altar boy, says he is at peace with his decision.

“It’s important to have your own faith and connection to God,” he said in an interview in his statehouse office. “At the same time, it isn’t just that faith you’re the governor of. … You’re governor of all the people.”

When the marriage bill was introduced, Baldacci argued that gay couples could get needed legal rights through civil unions, but his views evolved.

“I was creating a second-class marriage for certain people, which wasn’t right,” he said. “I wasn’t doing my duty to the constitution I swore to uphold.”

Baldacci hopes the campaign, as it gains national attention, will be illuminating and respectful rather than nasty.

“To divide us more, especially during difficult times, would hurt us — leave such scars that they could never be healed,” he said.