As public opinion shifts about gay marriage, opponents of the idea are shifting as well.

Minnesota lawmakers are bringing forward their proposal to constitutionally ban same-sex marriage, but they are paring down their demands.

Unlike previous years, the proposed amendment is limited to marriage, and does not address legal equivalents. That could open the door to legal recognition of civil unions and other non-marriage partnerships between gay couples.

"The language that we are proposing today doesn't do anything except say this is what we mean by marriage," said Sen. David Hann, an amendment co-sponsor. "In past years, there may have been desires to do other things."

The change could give the measure a better chance when it comes to the ballot.

The linguistic difference means that even if voters approved the amendment on the 2012 ballot, a future Legislature could permit legal arrangements between gay couples, including allowing same-sex couples the same legal rights as married couples.

While many conservatives and Republicans oppose civil unions as much as they do same-sex marriage, others in the nation have shifted on the subject. Where once a majority opposed gay marriage, recent Pew Research Center polls now find an even split. On civil unions, a "clear majority of Americans" say gay couples should have equivalent legal rights where their partners are concerned.

"That's now a less controversial issue with the public than gay marriage," said Carroll Doherty, associate director of Pew Research Center for the People & the Press.

That change could give the amendment, which has a Senate hearing Friday, more life if it reaches the ballot. If Minnesotans' opinions follow national trends and support civil unions, an amendment that forbids them could fail on that fact alone.

Tom Prichard, the executive director of the Minnesota Family Council, a key amendment backer, said they just want to "zero in" on marriage. Asked whether backers were fearful that banning civil unions would overreach, he said, outlawing other legal relationships does not "directly relate to the definition of marriage, which is the focus of the amendment." The proposed amendment defines marriage as the union of a man and woman.

Sen. John Marty, DFL-Roseville, thinks it could be more calculated.

Marty said backers may believe they would lose the ballot vote "for sure" if they tried to ban civil unions and all other legal relationships, as well as gay marriage.

"I think the public is changing around on this," Marty said.

Monica Meyer, executive director of OutFront Minnesota, points to evidence of that change in Minnesota.

A number of local governments, including Minneapolis, now allow gay couples to register domestic partnerships, said the director of the gay rights group. Since 1991, nearly 2,000 Minneapolis couples have registered as partners, according to John Stiles, spokesman for Mayor R.T. Rybak. About 400 have since dissolved their partnerships.

The registration doesn't give the couples much. It could be helpful in securing benefits from private companies and allows partners visitation rights at health-care facilities. But even that system could be on "legal shaky ground" if an expansive constitutional amendment passed, said Meyer.

For some gay rights groups, domestic partnerships and civil unions fall into the category of separate but not equal.

"Civil unions don't have the same legal protections," said Meyer. "At the end of the day, it is just not the same."

Rachel E. Stassen-Berger is a correspondent in the Star Tribune Capitol Bureau.