BOSTON — Lawmakers in Massachusetts, the only state where gay marriage is legal, voted yesterday to allow a proposed constitutional amendment to move forward that would effectively ban the practice.The amendment’s backers had collected 170,000 signatures to get a question on the 2008 ballot asking voters to declare marriage to only be between a man and a woman, but they still needed the approval of legislators in two consecutive sessions.

Yesterday, 61 lawmakers voted in favour of moving the measure forward, compared to 132 opposed. The amendment need 50 votes of support to advance.

If it makes it on the ballot and residents approve it, the constitutional amendment would leave Massachusetts’ existing same-sex marriages intact but ban any new ones.

About 8,000 same-sex couples have wed in Massachusetts since the Supreme Judicial Court ruled in 2003 that the state Constitution guarantees gays the right to marry. A few other states offer civil unions with similar rights for gay couples, but only Massachusetts allows gay marriage.

Backers of the amendment argue that it should be up to the people, not the courts, to define something as important as marriage. Supporters of gay marriage say the civil rights of a minority should not be put to a popular vote.

Democratic Gov.-elect Deval Patrick yesterday met with leading lawmakers and urged them to skip the vote, calling it a “question of conscience” and saying the amendment process was being used “to consider reinserting discrimination into the constitution.”

Since yesterday was the final day of the session, skipping the vote would have effectively killed the amendment effort.

Instead, the Senate president called for a vote shortly after opening the constitutional convention, though he left open a chance for parliamentary manoeuvres by gay marriage supporters to try to reverse the vote.

“I’m very proud that we took a vote,” said Democratic Sen. Sue Tucker, who opposed the amendment. “I think we owed the people that. At the same time, I’m also equally proud of my ‘no’ vote.”

Last fall, the Legislature had angered the amendment’s backers and Gov. Mitt Romney when it recessed without voting on the amendment. They appealed to the state Supreme Judicial Court, which said it was powerless to intervene but chastised lawmakers, saying they had shirked their constitutional duties by not voting at all.

Lawmakers arriving for yesterday’s vote were greeted outside the Statehouse by crowds of gay marriage supporters and opponents waving signs.

“Legislators are sent to Beacon Hill to vote on a matter, not to not vote on a matter,” said amendment backer Paul Ferro, 30, of Norton.

A sign in the crowd of amendment supporters nearby read, “Let the people vote,” while at the pro-gay marriage rally across the street, another sign read, “Let the people marry.”