Derek McCoy, the director of the Maryland Marriage Alliance, which opposes same-sex marriage, said: “I think what we’re going to prove here is marriage is on the table, and marriage does matter. And because it does matter, Marylanders are engaged.”

But supporters of same-sex marriage in Maryland say they have reason for optimism, too.

There has not been a state vote on the issue since President Obama voiced his support for same-sex marriage this year and the N.A.A.C.P. came out in favor of it.

“The two biggest factors for us this year are that it’s 2012, and public attitudes have continued to evolve,” said Josh Levin, the director of Marylanders for Marriage Equality. “When the president talked about how his position has evolved over the course of some years, there are a lot of people for whom that’s the case.”

The ballot language will also be different in Maryland. In the other 32 states where voters have been asked about the issue, the referendum question was phrased so that a vote in favor of the measure was a vote to reject same-sex marriage. In Maryland, ballots will ask the question in the affirmative and will explain that there will be an exemption for religious groups.

In January, a poll conducted by The Washington Post found that half of Maryland residents supported same-sex marriage. Since then, polls have suggested a rise in support — in large part, advocates believe, because more black voters have warmed to the idea.