ST. PAUL — It’s now up to voters to decide whether to ban gay marriage in Minnesota.

After nearly six hours of emotional debate, a proposed constitutional amendment that would define marriage as between a man and a woman was approved in the Minnesota House late Saturday night. It was the last legislative step needed to put the question on the statewide ballot in November 2012.

State law already prohibits gay marriage, but supporters of the proposed amendment said it’s 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.”

A rare quiet prevailed in the House chamber as members made emotional and often personal speeches in opposition to the amendment. The issue drew an unusually large crowd to the Capitol, where supporters and opponents traded loud chants earlier in the day but quieted considerably when the debate started around dinnertime.

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.

But fellow Republican Rep. John Kriesel described how losing his legs while serving in Iraq began a personal transformation of his views on the issue. He said he would have supported the amendment five years ago, but has since realized that the country for which he fought should not deny two people who love each other the right to marry.

“I’m pleading with you to vote no,” said Kriesel, R-Cottage Grove. “I’m begging you.”

Ban opponents made up the majority of observers who stayed late to watch the debate from the second floor of the Capitol, where televisions broadcasted a live feed. They could be heard from inside the House chamber singing hymns and occasionally cheering during pivotal moments of lawmakers’ speeches.

The debate had been postponed Friday after a pastor known for anti-gay comments delivered a controversial prayer on the House floor that prompted Speaker of the House Kurt Zellers to apologize.

During Saturday’s floor debate, 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.

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. He described being torn, and said his teenage daughter recently pointed out that she would be 18 by November 2012 — and she plans to vote against the ban.

“She said, ‘Dad, I think a person should be able to marry whomever they love whether it’s the opposite sex or not,'” Hamilton said.