“As Maine goes, so goes the nation” is a political cliché long since out of use.

But with Tuesday’s election there, both sides in the fierce debate over same-sex marriage are hoping the outcome not only favors them but sends a clear message to the rest of the United States.

In May, the Maine Legislature passed a law legalizing gay marriage, and after initially opposing it Gov. John Baldacci signed the measure. If approved, “Question 1” on Tuesday’s ballot would overturn the new law.

If the measure wins at the polls, it would continue a string of about 30 states where voters have rejected gay marriage. If it fails, Maine would join the handful of states (Massachusetts, Connecticut, Vermont, and Iowa) where legislatures and courts — not voters — have made same-sex marriage legal.

“This is significant on the national level because this is the first time voters are weighing in on a law where marriage has already been defined for them,” Jenny Tyree, a marriage analyst with the conservative lobbying group Focus on the Family Action, told the Bangor Daily News.

Advocates on both sides certainly see it as significant. Troops are being rallied and funds raised around the country by those opposed to gay marriage and those advocating “marriage equality.”

Polls show a very close contest, with those favoring same-sex marriage ahead in campaign contributions — much of the money coming from out-of-state, including California where activists hope to reverse Proposition 8 (which overturned that state’s gay marriage law).

The Roman Catholic church has been very active on the question. Those urging a “yes” vote on Question 1 are counting on a relatively large turnout among older voters (typical in off-year elections) since younger Americans poll more positively on same-sex marriage.

Meanwhile, the issue is stirring increased public and political activity around the country.

Also on Tuesday, voters in Washington State will decide on “Referendum 71,” which addresses the state’s new “everything but marriage” act providing benefits and rights for domestic partners to the same standard as married couples.

In New York State, Governor David Paterson is preparing legislation to legalize same-sex marriage there.

Senator Arlen Specter, the Republican turned-Democrat from Pennsylvania facing a tough reelection fight, this week reversed his position and says it’s now time to repeal the Defense of Marriage Act. “The Act is a relic of a more tradition-bound time and culture,” he wrote on Huffington Post.

Speaking to a gay rights group last week Senator Charles Schumer (D) of New York had this to say:

“Ten years ago, many thought that civil unions were about the best we could hope for. But the time for marriage has come,” Schumer told the Empire State Pride Agenda dinner. “I call on all of my colleagues — Democrat and Republican, in the Congress, in the state senate, in the state legislature, to support full marriage equality now.... Equality should know no bounds, and we must not rest until we have [gay] marriage in all 50 of these United States.”

Religious leaders on both sides of the issue spoke out this week in the District of Columbia, where a proposed measure would legalize same-sex marriage.

President Obama says he’s for ending the federal “Defense of Marriage Act” as well as the US military’s “don’t ask, don’t tell” policy banning open homosexuality in the ranks. But activists say he’s not doing enough to accelerate changes in federal policy.