ST. PAUL  — A historic vote Thursday in the Minnesota House positioned that state to become the 12th in the country to allow gay marriages and the first in the Midwest to pass such a law out of its Legislature.

Lawmakers approved it 75-59, a critical step for the measure that would allow same-sex weddings beginning this summer. It’s a startling shift in the state, where just six months earlier voters turned back an effort to ban gay marriage in the Minnesota Constitution.

The state Senate plans to consider the bill Monday and leaders expect it to pass there, too. Gov. Mark Dayton has pledged to sign it into law.

“It’s not time to uncork the champagne yet. But it’s chilling,” Rep. Steve Simon, a suburban Democrat who backed the bill, said at a raucous rally in the state Capitol rotunda minutes after the vote.

Rep. Karen Clark, the bill’s sponsor, said her only goal was equal treatment under state law for same-sex couples. In a deeply personal speech, the Minneapolis Democrat talked of the support she got from her own family after coming out as gay decades ago.

“My family knew firsthand that same-sex couples pay our taxes, we vote, we serve in the military, we take care of our kids and our elders and we run businesses in Minnesota,” she said.

Hundreds of supporters and opponents gathered outside the House chamber up to and during the debate, chanting and waving signs. They sang “We Shall Overcome” and the John Lennon song “Give Peace a Chance” — substituting the word “love” for “peace.”

Four of the House’s 61 Republicans voted for the bill, while two of its 73 Democrats voted no. None of the four Republicans committed support beforehand; one, Rep. Jenifer Loon, said she made up her mind during the three-hour House debate, in which lawmakers listened with rapt attention while their colleagues spoke.

“There comes a time when you just have to set politics aside and decide in your gut what is the right thing to do,” said Loon, whose suburban district southwest of Minneapolis voted strongly against last fall’s gay marriage ban. The other Republicans to vote for gay marriage also hail from suburban or exurban districts: Pat Garofalo of Farmington, David FitzSimmons of Albertville and Andrea Kieffer of Woodbury.

The two Democrats who voted no, Patti Fritz of Faribault and Mary Sawatzky of Willmar, represent largely rural districts where the gay marriage ban was backed by a majority of voters. But most of the Democrats from rural, more socially conservative areas ended up voting for the bill.

Opponents argued it would alter a centuries-old conception of marriage, and leave those people opposed for religious reasons tarred as bigots.

“We’re not. We’re not,” said Rep. Kelby Woodard, a Republican from Belle Plaine. “These are people with deeply held beliefs, including myself.”

House Republican Leader Kurt Daudt acknowledged that views on gay marriage are changing, but said the bill’s sponsors stood to alienate thousands of Minnesotans who still believe in the male-female definition of marriage.

“Hearts and minds are changing on this,” Daudt said. “But Minnesotans are still divided.”

That could be seen outside the House chamber, where supporters and opponents of the bill stood shoulder to shoulder and chanted with equal vigor. Gay marriage backers dressed in orange T-Shirts and held signs that read, “I Support The Freedom to Marry.” Behind them, opponents held up bright pink signs that simply read, “Vote No.”

Among the demonstrators was Grace McBride, 27, a nurse from St. Paul. She said she and her partner felt compelled to be there to watch history unfold. She said she hopes to get married “as soon as I can” if the bill becomes law. The legislation would allow her to do so starting Aug. 1.

“I have thought about my wedding since I was a little girl,” she said.

On the other side of the divide, Galina Komar, a recent Ukrainian immigrant who lives in Bloomington, brought her 4-year-old daughter and 1-year-old son to the Capitol to express her religious concerns.

“I do believe in God, and I believe God already created the perfect way to have a family,” Komar said.

Eleven other states allow gay marriages — including Rhode Island and Delaware, which approved laws in the past week.

Iowa allows gay marriages because of a 2009 court ruling. Leaders in Illinois — the only Midwestern state other than Minnesota with a Democratic-led statehouse — say that state is close to having the votes to approve a law, too.

But most other states surrounding Minnesota have constitutional bans against same-sex weddings, so the change might not spread to the nation’s heartland nearly as quickly as it has on the coasts and in New England.

The Minnesota push for gay marriage grew from last fall’s successful campaign to defeat the constitutional amendment that would have banned it. Minnesota was the first state to turn back such an amendment, after more than two dozen states passed one over more than a decade.

The same election put Democrats in full control of state government for the first time in more than two decades, a perfect scenario for gay marriage supporters to swiftly pursue legalization. The bill cleared committees in both chambers in March, at the same time a succession of national polls showed opposition to gay marriage falling away nationally.

“There are kids being raised by grandparents, single parents, two moms or two dads,” said Rep. Laurie Halverson, a Democrat from a suburb south of St. Paul. “Some of those folks are my friends. And we talk about the same things as parents. We talk about large piles of laundry, and how much it hurts to step on a Lego. That’s what we do, because we’re all families.”