The future of gay marriage in Minnesota is in voters’ hands.

After almost six hours of discussion on the House floor late Saturday night, legislators approved a proposed constitutional amendment that would define marriage as between one man and one woman. It was the last legislative step needed to put the issue on the statewide ballot in November 2012.

Rep. Jeanne Poppe, DFL-Austin, said the tone on the House floor before the vote was “solemn and serious.” Poppe, who voted against the amendment, said the five-hour discussion was unnecessary, especially because a budget agreement has not been reached.

“I don’t think it was necessary to bring up this issue, which is clearly a divisive issue,” she said. “I think it’s extremely sad and unfortunate that we spent the time and energy and effort on that.”

State law already prohibits gay marriage, but supporters of the proposed amendment said it is necessary to prevent judges or lawmakers from legalizing it in the future. Opponents said the constitution should be used to expand rights, not limit them, and predicted a long, divisive debate over the next 18 months.

The House voted 70-62 mostly along party lines in the GOP-controlled chamber, though four Republicans crossed over to vote ‘no’ while two Democrats voted in favor of the ban.

During Saturday’s debate, which drew hundreds of people to the Capitol, Rep. Karen Clark described her 22-year committed relationship with her female partner. The Minneapolis Democrat said they considered getting married in Iowa, where gay marriage is legal, so her ailing father could see her marry.

“Please don’t make me go off to Iowa,” she told her colleagues. “I was raised in Minnesota. I’m a child of Minnesota.”

After the vote, Clark said it was “a sad day for Minnesota.”

But Jason Adkins, executive director of the Minnesota Catholic Conference, said it was an important step and that “Minnesotans have been given the opportunity to have an important conversation about the future of marriage.”

Democratic Gov. Mark Dayton has no power to block the question from the ballot, but said before the vote that he would fight it. Dayton called the amendment, which the Senate approved last week, “un-Minnesotan.”

During Saturday’s floor session, many lawmakers spoke of their own marriages and families, gay relatives and friends, religions and military service, or facing discrimination and bullying as children.

Several said they worried that debate on the issue between now and November 2012 would leave gay youth feeling marginalized and vulnerable.

Rep. Steve Gottwalt, the bill’s sponsor, said voters should have the final word on the issue.

“This is not about hatred. It is not about discrimination or intolerance,” said Gottwalt, R-St. Cloud.

Among the few Republicans who spoke during the debate was Rep. Tim Kelly of Red Wing, who called the proposed amendment “an assault on personal freedom and choice” and a “giant step backward.”

Besides Gottwalt, the only other Republican to speak in favor of the amendment was Rep. Rod Hamilton of Mountain Lake.

Poppe admitted the Democrats talked more than the Republicans during the five-hour floor session, which added to the frustration of having not struck a budget deal.

“It seems it’s not likely that there’s an agreement yet,” Poppe said Sunday afternoon. “I’m still believing that it’s far away from us. I still believe we’re likely going to a special session maybe in a month’s time.”

“That’s just my own sense of what’s going on here,” she added.

— The Associated Press contributed to this report