For the first time in history, a major political party is formally supporting gay marriage, as Democrats approved a platform Tuesday that includes a “marriage equality” plank, setting the party in clear contrast to Republicans.

Democratic officials say the vote puts the party squarely in the “individual rights” camp and that it will use the platform to lead the country to acceptance of what supporters say is a basic right. The move comes just a week after Republicans, at their national convention in Tampa, approved a platform that specifically calls for a federal constitutional amendment banning gay marriage.

The positions are now clear: Republicans in opposition, Democrats in favor. It also leaves Democrats in the precarious position of energizing parts of their base for whom this is a key issue while potentially driving off more conservative voters in key swing states like North Carolina and Ohio.

Supporters here liken the Democratic plank to support for a civil rights plank in 1948. Democrats also see this as a chance to reach out to a wing of the party that has been stung in the past by passage — with then-President Bill Clinton’s signature — of the federal Defense of Marriage Act and constitutional amendments in several states, including Georgia, opposing gay marriage.

“Doing the right thing is never the wrong move,” Georgia delegate John Washburn of Avondale Estates said.

A spokeswoman for the Republican National Committee said the Democratic platform clearly illustrates the difference between the two parties.

“The Republican Party believes marriage is between a man and a woman, which is in line with many Americans,” Catherine Gatewood said.

The Democrats’ platform calls for “equal treatment under the law for same-sex couples.” It calls for repeal of the Defense of Marriage Act and rejects state and federal laws that discriminate against same-sex couples. The platform also says churches should be free of government intrusion in their decisions on administering marriage as a sacrament.

Six states — Connecticut, Iowa, Massachusetts, New Hampshire, New York and Vermont — along with the District of Columbia currently allow same-sex marriage, and three others have same-sex marriage laws that are on hold pending challenges. California’s constitutional ban on same-sex marriage has been ruled invalid by a federal appeals court, but that ruling is not being enforced pending appeal.

Nationally, support for gay marriage is growing, according to a poll released July 31 by the Pew Research Center, but not as quickly in the South.

The poll by the nonpartisan think tank found just 39 percent of Southerners support marriage equality while 52 percent oppose it. In every other region of the country, the poll found, a majority or plurality of voters support gay marriage. Still, Pew found, support from Southerners has grown by 8 percentage points in just four years.

Recent polling on the issue in Georgia has been sparse, but the state’s conservative nature makes marriage equality a tough sell. (In 2004, 76 percent of Georgians voted to amend the state’s constitution to ban same-sex marriage.) Facing that, Georgia delegates met privately before this week’s convention to discuss the platform and specifically the gay-marriage plank. Tuesday, the delegation voted unanimously for the platform.

Nationally, the Pew poll found gay marriage’s support strongest among Democrats, at 65 percent, compared with 24 percent of Republicans. Perhaps more importantly, 51 percent of independents surveyed now support the idea, compared with 44 percent in 2008.

Those numbers are significant, said Steve Perkins, an at-large delegate for Georgia from Atlanta.

“The party has embraced the inevitable,” he said. “The Republican Party is going to try and make hay with it when they can because it enthuses their base. At the same time, it ends up painting them into a corner politically.”

Republicans are already using the issue — and President Barack Obama’s support of gay marriage — to their advantage.

A super PAC called Campaign for American Values this week released a television ad in North Carolina — a battleground state — that features a couple accusing Obama of trying “to force gay marriage on the country,” and it ends with the husband urging his wife to “vote for someone with values” instead.

How the issue plays remains uncertain in other swing states, such as Ohio, where 87 of the state’s 88 counties backed a state ban on gay marriage in 2004.

“As of now, there is a shifting public perception on the matter, so it is not necessarily a clearly unpopular position for the party,” said Mark Caleb Smith, director of the Center for Political Studies at Cedarville University in Cedarville, Ohio.

Democrats do face the risk of losing some conservative voters and evangelicals who supported Obama in 2008, but the party and Obama are clearly targeting their base, Smith said.

“Social progressives strongly agree with the idea of gay marriage,” Smith said, giving Obama a chance to excite donors and volunteers.

For Georgia Democrats, the issue could be tricky. The party’s African-American base has traditionally been more conservative toward marriage than white Democrats.

The Rev. Alan S. Robinson, of Abundant Life Church of God in Christ in Atlanta, which has about 150 members, makes no bones about his opposition to marriage equality.

“We all stand together,” he said. “That’s just what we believe — that marriage is between a man and a woman. If a person feels like they have an alternative lifestyle, we’re not going to try to beat them down or dishonor them. We love them still, but we cannot promote the lifestyle of gay marriage.”

But Robinson said gay marriage is just one of several issues he has with the current administration. “I’m not sure how I will vote,” he said.

Bishop Donald E. Battle of Divine Faith Ministries International, based in Jonesboro, makes it clear he opposes gay marriage but still plans to vote for Obama.

“I do believe in the sanctity of marriage between a man and a woman, as I learned in the Bible,” said Battle, whose ministry has three locations in Jonesboro and Buford with a combined membership of 8,000. “I do still support my president and the Democratic Party. We don’t have to agree on everything, but we do agree on some things.“

Scott Huffmon, a political scientist at Winthrop University in Rock Hill, S.C., regularly polls South Carolina and the South. While there will be plenty of Southern voters who will not be “thrilled” with Democrats’ decision, he expects the impacts to be minimal.

“It’s still an issue for a lot of Southerners, but the people who feel very, very strongly about it really aren’t persuadable by Obama anyway,” Huffmon said. “The other folks who are not comfortable with same-sex marriage but are persuadable by Obama … that’s usually not going to be the tipping point for them.”