Maryland voters are poised to approve same-sex marriage at the ballot box next month, a potential watershed moment in the history of a right that has been granted by courts and state legislatures but never by a popular vote, a new Washington Post poll has found.

Maryland voters favor upholding the state’s gay marriage law by a nine-point margin, according to the poll, which could end a streak of defeats in more than 30 states and provide further evidence of the country’s evolution on the controversial topic. Recent surveys have also shown leads in Maine and Washington state, where voters will be presented with the same issue Nov. 6.

Voters in Maryland could also become the first state to approve a form of the Dream Act, which has been adopted in 13 other states but never been put to a statewide vote. The Post poll found that 59 percent of likely Maryland voters back the measure, which would allow undocumented imigrants to pay in-state tuition rates at public colleges; 35 percent are opposed.

It has been three years since voters in any state were asked to legalize same-sex marriage — the question failed narrowly in Maine in 2009. Opponents have said they are confident that voters will reject the three state measures yet again. But advocates have long been looking at next month’s election as a potential breakthrough that capitalizes on momentum from President Obama’s endorsement of same-sex marriage earlier this year.

They received another boost Thursday when a federal appeals court in Manhattan ruled that the Defense of Marriage Act, the federal law that defines marriage as between a man and a woman, was unconstitutional. The issue is expected to reach the U.S. Supreme Court soon.

Immigration and same-sex marriage on the Maryland ballot

“The last barrier we need to overcome as a small minority is winning a majority vote on the ballot,” said Evan Wolfson, president of Freedom to Marry, a national gay-rights group. “There’s definitely a pathway to victory in these three states, but we can’t take anything for granted.”

Although The Post poll found that likely voters favor a ballot question on whether to uphold Maryland’s same-sex marriage law 52 percent to 43 percent, the race is hardly over. Historically, opposition to gay nuptials at the ballot box has been stronger than polls suggested, and an expected ad blitz from opponents of Question 6 has barely begun.

“We’re feeling very positive,” said Derek McCoy, the leader of the Maryland Marriage Alliance, which is heading up the opposition. “We’re going to help people understand what the consequences are of redefining marriage, and they’ll realize this isn’t a very smart thing to do.”

Opponents plan to press the argument that allowing gay unions would not only undermine the institution of marriage but also affect school curricula and infringe upon religious liberties, even as supporters in Maryland say they have gone to great lengths to protect against that.

The law, championed by Gov. Martin O’Malley (D), was passed by the legislature this year and swiftly petitioned to the ballot by McCoy’s group.

Even a couple of victories next month would yield a mixed record this year nationwide for supporters of same-sex marriage. In the spring, North Carolina became the 31st state to adopt a ban on gay unions. Minnesota voters will be presented with the same proposition Nov. 6.

Still, national polling has shown a clear trend in the direction of greater acceptance of gay unions, driven in part by widespread support from younger voters.

Maryland referendum primer

The Post poll found that 64 percent of Maryland voters ages 18 to 39 support Question 6. That drops to 51 percent of those ages 40 to 64, and 40 percent of those 65 and older.

“I don’t really understand what the big deal is about it,” said Christopher Valis, 24, a community college student in Harford County. “It’s a basic civil right, and it really, really bugs me that it’s not already allowed.”

There has also been some movement nationally among African American voters — a trend less evident in the Maryland poll — since Obama’s announcement and the NAACP’s endorsement this year of same-sex marriage.

In a state where African Americans make up a larger percentage of the electorate than anywhere outside the Deep South, both sides in Maryland have been heavily targeting black voters.

In their television ads, proponents have featured black ministers and civil rights leaders, arguing that allowing gay people to wed is the fair thing to do whether one personally approves or not.

Opponents of Question 6 have networked for months through black churches. In a new television ad, they feature Angela McCaskill, the chief diversity officer at Gallaudet University, an African American who was put on administrative leave for signing the petition to put Maryland’s same-sex marriage law on the ballot.

Religion plays a major role in voters’ views on the matter, The Post poll found.

Among opponents of same-sex marriage, two-thirds say their religious beliefs and opinions are the chief influence on their views.

“The Bible says there’s only one marriage, the covenant between a man and a woman,” said Melissa Smith, a 61-year-old retired elementary school principal who lives in Laurel. “They should have their beneficiaries; their families shouldn’t be able to ban them from each other’s deathbeds, but I don’t think they need to be married in order to have that.”

Supporters cite more varied motivations, including personal and educational experiences, and family and friends. Just 9 percent of supporters say religion is the biggest influence on their views.

Josh Levin, the campaign manager for Marylanders for Marriage Equality, said he thinks it is premature to celebrate despite promising poll numbers for his side.

“We’re only at 52 percent, and anyone who thinks we’re going to be up nine points at the end of this doesn’t know the history,” Levin said.

Kamah Woelfel, 31, is among the state’s African Americans whose views have evolved on the matter in recent years. A cousin came out of the closet, she said, and she came to have friends at college and later at the rehabilitation hospital where she works who were openly gay.

The issue remains a divisive one at family gatherings for Woelfel, a Randallstown resident who was raised as a Catholic. The news is always on, and politics is an inevitable topic of conversation. Her 64-year-old mother and three siblings, ages 28 to 42, have all switched their views to favor same-sex marriage. Her father remains opposed.

“He definitely is still trying to sway us back, but I say, ‘Dad, come on — it’s 2012.’ ”

In the Post poll, a gap remains between the views of white voters in Maryland, who favor gay nuptials 56 percent to 39 percent, and black voters, who tilt against it. In the survey, 42 percent of African American voters support the measure, and 53 percent oppose it.

Among Democrats, the racial divide is more pronounced. While 76 percent of white Democrats back Question 6, support is 40 percent among black Democrats. Republicans in the state oppose the measure by 2 to 1, while independents support it 2 to 1.

The telephone poll was conducted Oct. 11-15 among a random sample of 1,106 Maryland adults. Interviews were conducted on conventional land-line and cellular telephones, and in English and Spanish. The sample of 934 registered voters and 843 likely voters each have a margin of sampling error of plus or minus four percentage points.

Carol Morello, Rachel Karas, Jon Cohen and Scott Clement contributed to this report.