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Gay-rights activists, conservative leaders and media from around the globe converged on the Massachusetts Statehouse for a historic session Wednesday in which lawmakers will take up a constitutional amendment to ban gay marriage (search).

As the hours ticked down, Senate leaders feverishly sought a middle ground, proposing a compromise that would ban same-sex marriage but establish civil unions.

"We should not engage in a divisive, all-or-nothing debate that may end by eliminating all rights for same-sex couples," Democratic Senate President Robert Travaglini and Republican Senate Minority Leader Brian Lees wrote fellow lawmakers Tuesday.

The compromise prompted almost immediate criticism, including from House Speaker Thomas Finneran (search), who called it "highly inappropriate" to use an amendment to craft legislation or pass new law — like one establishing civil unions.

The gay-marriage issue has created an unprecedented spectacle at the Capitol: As many as 4,000 spectators and 300 media members are expected to attend the start of the constitutional convention, and a furious lobbying effort was already under way.

Christian conservatives used a dolly to haul in more than 18,000 petitions signed by citizens from across the country urging lawmakers to pass the amendment.

Meanwhile, children of gay couples traveled to the Statehouse to plead with the Senate president "not to write discrimination into our constitution."

"I've never seen anything like this," said Charles Rasmussen, spokesman for Finneran, a Democrat who supports the amendment. "And I'm told this building has never seen this kind of scrutiny from the national media that anyone can remember."

Camera crews from London, Japan and Spain are seeking credentials for the event, and authorities planned to beef up security to handle the crowds.

Massachusetts put itself at the very center of the gay-marriage debate when the Supreme Judicial Court ruled 4-3 in November that gays should be guaranteed the benefits of marriage. Lawmakers thought that Vermont-style civil unions might suffice, but the court issued an advisory opinion last week that left no doubt: Only full-fledged gay marriage would pass constitutional muster.

That cleared the way for the nation's first legally sanctioned same-sex weddings by May.

At the constitutional convention, the House and Senate will meet together to consider 10 proposed constitutional amendments. The gay-marriage issue is near the bottom of the agenda and might not get to a final vote for days.

Another proposal on the agenda is an amendment that could require the state's judges to be elected rather than appointed — an issue that has taken on added significance because of the court's polarizing stance on gay marriage.

If approved by the Legislature during this session, the gay-marriage amendment would have to again be ratified by lawmakers during the 2005-06 session before it could wind up on the November 2006 ballot.

The last time Massachusetts lawmakers in the heavily Roman Catholic state had a chance to weigh in on the issue of gay marriage was in 2002, when the constitutional convention was gaveled to a close before any vote took place. Near-brawls erupted among citizens who attended and raised voices were heard in the normally sedate chamber.

The Senate president at the time used parliamentary procedures to prevent a debate or vote on the gay-marriage ban. Travaglini, who does not support gay marriage but is in favor of civil unions, promised not to use such maneuvering this time.

On Tuesday, lawmakers circulated proposed changes to the amendment, hoping to secure the necessary 101 votes among the 199 sitting lawmakers to get it passed. The proposed compromise establishing civil unions had critics on both sides of the issue.

"We find that reprehensible," said Ron Crews, president of the Massachusetts Family Institute (search), which opposes gay marriage. "We need legislators who will have the courage to take a stand to preserve and protect marriage as it is currently worded. We would encourage the legislature not to cloud this with any other language at this date."

Gay-rights advocates said the compromise does nothing but camouflage a bigoted amendment.

"At the end of the day, they're writing discrimination into the constitution and putting a fresh coat of paint on it," said Amy Hunt, director of the LGBT Aging Project (search), a state gay-rights group.