Conservative groups and some state lawmakers pleaded with a federal judge Wednesday in an 11th-hour bid to stop the nation's first state-sanctioned gay marriages (search) from taking place next week in Massachusetts.

Mathew Staver, president and general counsel of the Florida-based Liberty Counsel (search), argued the state's high court stepped outside its jurisdiction when it ruled in November that gay marriage should be legal in Massachusetts.

"It's an unusual time that we live in, and we're asking this court to intervene to prevent this constitutional train wreck," Staver told U.S. District Judge Joseph Tauro.

Assistant Massachusetts Attorney General Peter Sacks (search), arguing on behalf of the Supreme Judicial Court, said the state court based its ruling on an interpretation of the state constitution, and the case does not belong in federal court.

"These are pure questions of state law," Sacks said. "There is no jurisdictional basis for this court to intervene or second-guess the SJC's ruling on a core matter of state law."

The judge said he would issue a decision Thursday afternoon or Friday morning. Both sides said they will appeal if necessary.

The Massachusetts high court said city and town clerks could begin issuing marriage licenses to gay couples Monday. Gov. Mitt Romney (search) has threatened clerks with legal action if they do not limit licenses to Massachusetts residents, but officials in Somerville, Worcester and Provincetown, a gay tourist hot spot on Cape Cod, have said they will issue marriage licenses to out-of-state couples.

The Legislature has given preliminary approval to a constitutional amendment that would ban gay marriage and legalize civil unions, but voters will not get to weigh in on the amendment until November 2006 at the earliest.

Plaintiffs in the suit included Robert Largess, vice president of the Catholic Action League, and 11 Democratic and Republican lawmakers. Besides Staver's Florida-based group, lawyers from conservative legal groups in Boston, Michigan and Mississippi are working on the case.

Staver predicted constitutional chaos during the 21/2 years before residents could vote on a gay marriage ban, but the judge likened the gay marriage issue to the struggle for racial integration in the 1950s and '60s.

"They said it was going to be chaos, it's going to be the end of the world," the judge said. "It hasn't been."

Conservative groups may be trying to make a point, but "there's very small chance it will be anything other than a symbolic point," said David Yas, an attorney and editor of Massachusetts Lawyers Weekly. "I wouldn't call it a frivolous lawsuit. But I would say the lawyers involved are likely well aware it's a big-time long shot."

In other developments Wednesday, the Louisiana Senate fell one vote short of passing a proposed amendment to the constitution that would ban gay marriage and civil unions.

The amendment's sponsor can try to round up more votes, while a similar measure is awaiting debate in the House.