MONTPELIER, Vt. -- Vermont, the first start to have civil unions, on Tuesday became a pioneer again as the first state to legalize gay marriage through a legislature's vote, suggesting growing popular acceptance of the idea.

The state House of Representatives barely achieved the votes necessary to override Gov. Jim Douglas' veto of a bill that will allow gays and lesbians to marry beginning September 1. Four states now have same-sex marriage laws and other states soon could follow suit.

Bills to allow same-sex marriage are before lawmakers in New Hampshire, Maine, New York and New Jersey. The three other states that allow same-sex marriage -- Connecticut, Massachusetts and Iowa -- each moved to do so through the courts, not legislatures.

"For a popularly elected legislature to make this decision is a much more democratic process" because lawmakers have to answer to the voters every other November, said Eric Davis, a retired Middlebury College political science professor.

California briefly allowed gay marriage after its highest court legalized it, but it was reversed after a public vote.

Courts typically deal with arcane points of constitutional law. While legislatures debate some of the same principles, the process may become much more personal. In Vermont, some of the most gripping debate came when gay and lesbian lawmakers took to the House floor last Thursday and told their own personal love stories.

Getting gay marriage approved in a political, rather than purely legal, forum is a big step, said Boston University law professor Linda McClain, an expert on family law and policy. "What may give courage to other legislatures is that this legislature managed to do it," she said.

She added that using the civil rights language of equality -- the measure in Vermont was dubbed the marriage equality bill -- could help make gay marriage more acceptable elsewhere.

Opponents said they, too, believe activists will be emboldened in other states. The action comes just days after the Iowa Supreme court ruled that not permitting gay marriage there was unconstitutional. Gay marriage is not recognized by the federal government under the Defense of Marriage Act.

"To the millions of Americans who care about marriage, we say get ready: President Obama and Democrats will use Vermont as an excuse to overturn the bipartisan federal Defense of Marriage Act," said Brian Brown, executive director of the National Organization for Marriage, which waged a radio campaign against the measure. "The next step is to ask the Supreme Court to impose gay marriage on all 50 states."

The Defense of Marriage Act, signed into law by President Bill Clinton in 1996, defines marriage as a legal union between a man and a woman, and provides that states need not recognize the marriage of a same sex couple from another state.

To date, the same-sex marriage movement's main gains have been in New England, which some attribute to Yankee liberalism and the gradual acceptance of gay relationships after Vermont's groundbreaking civil unions law took effect in 2000.

Douglas had announced his intent to veto the gay marriage bill two weeks ago, saying he believed marriage should be limited to a man and a woman and calling the issue a distraction during a time when economic and budget issues were more important.

In Tuesday's vote, a "yes" was needed from two-thirds of those present to override the governor's veto. The goal was easily achieved in the Senate, which voted 23-5, but in the House it was much closer, 100-49.

The speaker's announcement of the results to a packed Statehouse chamber, set off whistles and cheers among supporters whose hopes had been temporarily dashed last month when the Republican governor announced he would veto the measure if it passed the Legislature.

Among those celebrating were former state lawmaker Robert Dostis and his longtime partner, Chuck Kletecka. Dostis recalled efforts to expand gay rights dating to an anti-discrimination law passed in 1992.

"It's been a very long battle. It's been almost 20 years to get to this point," Dostis said. "I think finally, most people in Vermont understand that we're a couple like any other couple. We're as good and as bad as any other group of people."

Dostis said he and Kletecka will celebrate their 25th year together in September.

"Is that a proposal?" Kletecka asked.

"Yeah," Dostis replied. "Twenty-five years together, I think it's time we finally got married."

Craig Bensen, a gay marriage opponent who had lobbied unsuccessfully for a nonbinding referendum on the question, said his side was outspent by supporters by 20-1.

"The other side had a highly funded, extremely well-oiled machine with all the political leadership except the governor pushing to make this happen," he said. "The fact that it came down to this tight a vote is really astounding."

The measure had only 95 "yea" votes when it passed the House on Friday. But some changed their votes Tuesday.

Democratic Rep. Jeff Young, who voted no twice because he is philosophically opposed to gay marriage, joined most other Democrats in voting to override Douglas' veto.

"I think if I wanted to continue my career here and have any chance of being effective, I had to vote with my caucus," he said.

Democratic Rep. William Lippert, a gay man, championed both the 2000 civil unions bill and this year's gay marriage legislation.

"It's been an incredibly powerful personal journey," Lippert said. "I consider it my personal great good fortune to be a member of the Vermont Legislature under the leadership of speakers who have in fact prioritized civil rights for the community of which I'm a part. It touches me deeply."