BOSTON -- During a Constitutional convention Thursday, legislators could vote on whether to put the question of banning same-sex marriage on the ballot in 2008.

NewsCenter 5's Janet Wu reported that there's a lot of head counting going on at the Statehouse. Republican leaders were summoned to the governor's office. Those rethinking their votes also were called in for a chat. Gay marriage advocates said that they are within two to four votes of killing the amendment for good.

"We're talking to as many people as we can," Lt. Gov. Tim Murray said.

"I've opened up to listening to people. I was pretty stubborn about the way that I felt," Rep. Paul Kujawski said.

Weymouth's state senator supported the amendment last time. Most of the 5,000 calls and letters he's received urge him to stay with that vote, yet he's thinking of switching.

"I hate to see us take something away -- a right that's have been granted. Creates an interesting class of people already married. Those people become dinosaurs," Sen. Robert Hedlund said.

Others rumored to be considering a change of their anti-gay marriage vote quashed that gossip.

"No wiggle room in your position at this point?" Wu asked.

"No, not at this point," Rep. Paul Donato said. "You never know what the future will bring in this business."

Meanwhile, national political leaders are lobbying hard. House Speaker Nancy Pelosi, Sen. Edward Kennedy and former Gov. Bill Weld don't want the issue on the same ballot as the presidential race next fall. It would only complicate the campaigns of some candidates.

"I don't see what advantage is for anyone to take it up in a presidential year," Sen. Richard Tisei said.

"The chance we have for survival is the 57 legislators who are standing firm under unprecedented pressure," said Evelyn Reilly, of the Massachusetts Family Institute.

"This thing is nip and tuck. We could absolutely see a scenario where we could with tomorrow. It is absolutely doable, but it hasn't happened just yet. We don’t have all the votes locked in yet, and until we do, none of us are going to sleep well this evening," said Arline Isaacson, of MA Equity.

Gov. Deval Patrick has made it clear that he wants a vote on Thursday, and he wants the amendment killed. Feeling the most pressure is House Speaker Sal DiMasi, who claims there won't be a vote unless he knows he can deliver.

But he doesn't control the gavel, the Senate president does, and she's promised a vote one way or the other, although it may not be Thursday.