Maine lawmakers from South Portland and Cape Elizabeth are showing early support for a gay-marriage bill introduced last week in the Legislature.

The legislation, proposed by Democratic state Sen. Dennis Damon of Trenton, would make Maine the third state to allow same-sex marriage. Massachusetts and Connecticut are the other two.

The proposed Maine law essentially redefines marriage as a legal union between two people rather than between a man and a woman.

But some Republican lawmakers already are gearing up for a fight, proposing an amendment to the state Constitution that defines marriage as a partnership between a man and woman.

The battle could send the question to a statewide referendum, says South Portland Rep. Terry Morrison, a Democrat who supports Damon’s bill.

“A lot of the arguments against this revolve around religion,” Morrison said. “But for me, this is not about a religious issue but about a civil partnership.”

Morrison said he will actively work to get the bill passed, talking to constituents and the press about why he believes it is important.

Morrison noted that a “civil marriage” bill would give same-sex couples the same legal protections and benefits that heterosexual couples have.

Morrison ran on a platform of supporting civil rights. He notes that legalizing same-sex marriage would enable spouses to enroll in a partner’s insurance plan, speak for a partner sick in the hospital and have common property rights.

Maine has a domestic partnership registry that’s open to gay couples. But it does not carry the same legal protections and benefits that marriage does. Legal protections for married couples include recognition and support of the couple as an economic entity for taxes, financial transactions and government benefits.

“I’ve been saying to constituents that I believe that two adults of legal age who are not related by blood should have the opportunity to express their love and interest in spending their lives together by committing themselves to a state-condoned civil marriage,” said Sen. Larry Bliss, a South Portland Democrat.

Bliss says Damon’s bill allows for civil marriages outside a church or religious institution.

“I do not believe that we should require religious organizations to ‘bless’ this civil marriage, but I believe that it is an important expression of people’s love and the state’s interest in ensuring equality.”

Rep. Cynthia Dill echoes Bliss’ assessment. The Cape Elizabeth Democrat said she believes “any rights conferred on citizens should be equally applied and enforced, including rights associated with marriage.”

At the same time, Dill said, she recognizes same-sex marriage may conflict with some religious beliefs, and that “churches should not be expected to accommodate gay marriage.”

Damon, who introduced the bill, said in a press conference that it is “long overdue,” in response to questions about the timing during a difficult budget year. Lawmakers are grappling with an $838 million shortfall.

Dill, a civil rights lawyer, agrees. She says that “there is always a time and place for civil rights,” noting there is an economic benefit to Maine when gay couples come to the state to marry and vacation.

“Welcoming same-sex couples is a way to foster” economic growth, she said.

Rep. Bryan Kaenrath, D-South Portland, said he is not familiar with the details of the bill but supports the concept and goal. “It’s a matter of fairness and treating people equally,” he said.

Rep. Jane Eberle, D-South Portland, said she personally supports the bill but will talk and listen to constituents before deciding how to vote.

“Personally, I support the bill. I don’t see a reason why people who love each other can’t be married to each other in a civil marriage. But I also will listen to constituents and balance my conscience with what they are saying,” Eberle said.

“I need to listen to the wishes of the community. I know where I stand but this is not about my personal opinion.”

Eberle’s position is similar to that of Gov. John Baldacci, Maine’s top Democratic leader. The governor issued a statement last week saying he will pay close attention to the debate but has yet to make up his mind on whether he supports same-sex marriage.

Baldacci has not said whether he would sign or veto the bill if it passes.

Maine is among a few New England states expected to consider same-sex marriage bills this year. A bill was introduced this year in the New Hampshire Legislature.

Similar bills are planned for Vermont and Rhode Island, according to the Gay and Lesbian Advocates and Defenders, a legal advocacy group.

The group’s goal is to pass same-sex marriage laws in all six New England states by 2012.

The Roman Catholic Diocese of Portland and the Maine Family Policy Council, formerly the Christian Civic League of Maine, have vowed to fight the bill and also to support a repeal, if it becomes law.