BOSTON — Massachusetts’s entire high court should decide whether to force lawmakers to take action on a proposed constitutional amendment to ban gay marriage, one justice decided yesterday.

Justice Judith Cowin made the ruling after hearing arguments on last week’s request by Governor Romney and other gay-marriage opponents to force the lawmakers to decide whether voters can consider the proposal in 2008.

A hearing before the seven-member Massachusetts Supreme Judicial Court — the same panel that said gay marriage was legal in 2003 — was set for December 20.

Supporters have gathered more than 170,000 signatures of people in support of the proposed amendment, which would define marriage as the union of a man and a woman. It would ban future gay marriages in Massachusetts but leave existing same-sex marriages intact.

Lawmakers postponed action on the proposed ballot question until January, prompting Mr. Romney’s request for court intervention.

“Governor Romney believes it is the court’s responsibility to step in to protect the right of the people to petition for a constitutional amendment and to have it placed on the ballot for a vote,” spokesman Eric Fehrnstrom said. “The fact the full court has agreed to hear the matter on an expedited basis indicates they recognize the important issues involved.”

The attorney general’s office declined comment.

An attorney for Mr. Romney and others who support the measure, John Hanify, had told Justice Cowin during yesterday’s hearing that the state legislature has a history of ignoring voter-initiated petitions. Lawmakers recessed without voting on a similar question in 2002 and also used the tactic to block ballot referendums on topics such as abortion and term limits for office holders.

Assistant Attorney General Peter Sacks had said separation of powers and the court’s own precedent indicate the court should not force lawmakers to vote.

The proposal would need the approval of only 50 of the 200 legislators during the current session, then again in 2007, to continue to the November 2008 ballot.

Opponents of the question, including powerful House Speaker Salvatore DiMasi, feared they didn’t have the 151 votes needed to kill the measure and instead called for a vote to recess the joint House-Senate session until January 2. Lawmakers approved the recess vote by 109–87.

Since gay marriage became legal, more than 8,000 same-sex couples have tied the knot in Massachusetts, the only state to allow gay marriage.

Mr. Romney, whose term ends January 4 and who has been laying the groundwork for a 2008 president run, was in Miami yesterday for a meeting of Republican governors.