Boston ? In a suspense-filled final day of the legislative session, Massachusetts lawmakers kept alive a proposed constitutional amendment Tuesday that would put a stop to gay marriage in the only state that allows same-sex couples to wed.

The vote came after weeks of mounting legal and political pressure on legislators from both sides in the debate.

With a combination of parliamentary maneuvering, flip-flopping and brinksmanship, lawmakers gave the first round of approval necessary for the amendment to appear on the ballot in 2008. The measure still needs the endorsement of the next legislative session.

If the amendment makes it onto the ballot and residents approve it, it will leave Massachusetts’ 8,000 existing gay marriages intact but ban new ones.

“This is democracy in action. It’s not a vengeance campaign. It’s not a hate campaign. It’s just an opportunity for the people to vote,” said Kris Mineau of the Massachusetts Family Institute, a conservative group that opposes gay marriage.

If lawmakers had failed to act on the amendment Tuesday, the measure would have died, and opponents of gay marriage who collected more than 120,000 signatures to try to put the issue on the ballot would have had to start over again.

The pressure on lawmakers came from all sides: Gay rights activists and Democratic Gov.-elect Deval Patrick called on the Legislature to let the measure die without a vote. Gay rights opponents – and Massachusetts’ highest court – demanded an up-or-down vote.

The state Supreme Judicial Court – the same court that ruled in 2003 that gays have a constitutional right to marry – declared last week that lawmakers had shirked their constitutional duties by refusing to vote on an amendment submitted by the people. But the justices acknowledged they had no authority to force action.

To advance to the next round, the amendment needed the approval of only 50 of the 200 members of the Legislature. On Tuesday, 62 lawmakers voted in favor, while 131 were opposed.

Arline Isaacson, co-chairwoman of the Massachusetts Gay and Lesbian Political Caucus, vowed to continue the fight into the next session to ensure the question is not put on a statewide ballot.

“We have no choice. We’re talking about our lives,” Isaacson said. But she acknowledged: “It’s a huge task. We might not be able to do it.”