Accord said to lack firm majority

A proposal to ban gay marriage and establish civil unions that won three roll-call votes during Thursday's Constitutional Convention lacks a clear majority of committed backers, a Globe analysis of the votes suggests.

Even though the proposed constitutional amendment was supported by large majorities Thursday, just 66 lawmakers out of 199 in the Legislature have voted consistently to support an amendment that both bans same-gender marriages and establishes civil unions.

Another 12 legislators have voted for any measure that would ban gay marriage, whether or not civil unions are included, bringing the number who could be counted on to support the amendment to 78, the analysis shows.

The comfortable margins by which the amendment passed on Thursday reflect short-term strategies employed by gay-marriage backers and opponents. Gay-marriage supporters were attempting to deflect rival proposals they viewed as more harsh to same-sex couples, while their opponents were maneuvering to keep the debate going and their future options open

Neither group can be counted on to ultimately back the amendment, the analysis suggests.

The measure must garner at least 101 votes to move forward, a figure that seems dauntingly large, given the ideological gridlock on Beacon Hill over the issue of same-sex marriage. Still, the amendment is now just one roll-call vote away from moving on to next year's Legislature, which must also approve the proposal before it can go to the voters.

The so-called compromise amendment was sponsored by House Speaker Thomas M. Finneran and Senate President Robert E. Travaglini. Speaking with reporters after Thursday's debate, Travaglini said he remained confident that his amendment would pass when the Legislature reconvenes in constitutional convention March 29.

"I believe we've overcome significant hurdles to get to this point," Travaglini told the Associated Press. "I would hope that the road gets somewhat smoother and that we have encountered all of the bumps along the way."

But even as Travaglini and Finneran continue their efforts to win over colleagues, those who oppose any amendment to the constitution banning gay marriage hope to continue the momentum they have generated thus far. That group, which stood at roughly 55 lawmakers a month ago, now stands at 77, Thursday's results show. Many of those who joined this group last month voted for amendments to ban gay marriage but establish civil unions. Now, it appears, they are willing to back the effort to prevent any amendment from reaching the ballot.

Senator Jarrett T. Barrios, who supports same-sex marriage, said he hopes to persuade several colleagues in the next two weeks that, even if they oppose gay matrimony, it would be unwise to amend the constitution to take away a minority group's rights.

"There's about 10 to 15 people who we have already picked up because they are absolutely against writing discrimination into the constitution regardless of their own view of gay marriage," said Barrios, a Cambridge Democrat.

Thursday's votes revealed the Barrios camp's strategy: After the group voted for the Finneran-Travaglini measure twice, it withdrew its support in an unsuccessful bid to kill it. If it had prevailed, no further action on a gay marriage amendment would have been allowed this year.

In addition to the maneuvering by the Barrios camp to undermine the Finneran-Travaglini amendment, questions exist about how faithful a group of nearly three dozen House members will remain to the measure.

Indeed, several of the 32 House Democrats who joined Finneran Thursday night in support of the amendment openly acknowledge they would prefer to ultimately approve a measure that provides no guarantee of civil unions.

When the convention resumes, lawmakers will be able to float competing ballot questions.

Representative Brian P. Wallace, a Boston Democrat who voted for the Finneran-Travaglini proposal Thursday night, said afterward he hopes that an amendment sponsored by Representative Paul Loscocco, a Holliston Republican, makes it the floor. That measure would ban gay marriage while directing the Legislature to create civil unions at a later date, leaving it up to lawmakers what rights and benefits those unions would provide. Other wild cards make predicting the outcome of the gay marriage debate difficult.

For example, liberal-leaning lawmakers, despite their strategizing to kill the Finneran-Travaglini amendment, may in the end sign on to it if they decide it is the best they can do and then fight it in next year's legislative session.

Conservative legislators, too, might feel obligated to sign onto such an amendment, if it appeared to be the only way to send a measure to ban gay marriage to the ballot box in November 2006.

A spokesman for Governor Mitt Romney, who opposes civil unions and is often an ideological beacon to Republicans in the House, said it is more important to define marriage as the union of a man and a woman than to preclude civil unions.