BOSTON (AP) – The reins of leadership in the Massachusetts House are changing from a conservative opponent of same-sex marriage to a socially liberal gay rights champion, just months before the next round in the state’s same-sex marriage debate begins.

Rep. Salvatore DiMasi, a Boston Democrat, was a leading advocate for the state’s 1989 gay rights bill, which barred discrimination based on sexual orientation, and a strong supporter of the state high court decision legalizing same-sex marriage this year.

Outgoing House Speaker Thomas Finneran, D-Boston, who resigned the speaker’s job after eight years to lead a biotechnology trade organization, is an outspoken opponent of same-sex marriage who sponsored a constitutional ban earlier this year.

“We’re ecstatic,” said Arline Isaacson, co-leader of the Massachusetts Gay and Lesbian Political Caucus. “While this certainly does not guarantee a change in the outcome, it sure as heck helps.”

In January, the reconstituted Legislature will convene for the second phase of debate on a constitutional amendment, which would ban same-sex marriage but legalize civil unions if approved by voters in November 2008. The Legislature gave preliminary approval to the amendment earlier this year after more than 30 hours of debate.

Even lawmakers who support same-sex marriage were dubious, however, about whether a change at the top would have any impact on the rank-and-file, who were forced to stake out their position on same-sex marriage repeatedly this year.

“Each person has only one vote,” said Rep. Lida Harkins, D-Needham, assistant majority floor leader and a supporter of same-sex marriage. “So I don’t know that his being there changes the numbers that much. I think that really is decided by who gets elected in November.”

All 200 legislative seats are up for grabs in the fall elections.

Kris Minneau, leader of the Massachusetts Family Institute, said DiMasi needs to heed the wishes of citizens who support the traditional definition of marriage as a union between one man and one woman.

“We hope he will be receptive to what a majority of the citizens of Massachusetts desire in terms of traditional family values,” said Minneau, whose organization led the charge against same-sex marriage during this year’s constitutional convention. “We do have a constitutional amendment process in effect, and we do look forward to the speaker carrying out his duties in accordance with the constitution.”

What impact this change in leadership will have on the course of business in the traditionally conservative House remains to be seen. The House, although overwhelmingly Democratic, has tended toward social conservatism, due to the influence of Finneran and other Catholic lawmakers.

“Our work is still cut out for us, but at least now we will have a chance to get bills debated,” said Melissa Kogut, executive director of NARAL Pro-Choice Massachusetts. “Speaker Finneran has been a major obstacle for us in moving legislation forward.”

Legislation that supported abortion rights or extended rights to GLBT citizens have repeatedly been blocked from consideration on the House floor after receiving approval in the more liberal Senate.

Finneran repeatedly blocked the creation of buffer zones around abortion clinics as well as legislation that would require insurance companies to cover the cost of birth control pills and other female contraceptives. For years, he also blocked the extension of domestic partnership benefits to same-sex couples.

“Fair-minded people in Massachusetts can sleep easier in Massachusetts tonight because it will be a lot harder for people who want to write discrimination into our constitution,” said Sen. Jarrett Barrios, D-Cambridge, who is gay. “[DiMasi] has a long history of supporting fair treatment for people in the commonwealth.”

Gov. Mitt Romney, a Republican who shares Finneran’s opposition to same-sex marriage, said he hoped the new speaker would allow lawmakers to vote their conscience on social issues.

“I think people in the commonwealth expect the legislators to allow them, the people, to have the final say on this important issue,” Romney said.