A referendum on Maryland lawmakers’ decision to legalize same-sex marriage moved from the realm of the likely to a near certainty on Tuesday as opponents turned in what they said were over 113,000 signatures — more than twice the number needed to qualify the law for the November ballot.

A coalition of religious leaders and conservatives organized to oppose gay marriage said weeks ago that they would easily beat Maryland’s first deadline on Thursday to file more than 18,000 signatures.

But with two days to go, opponents said that President Obama’s recent announcement that he supports same-sex marriage appeared to have had the effect of not only invigorating supporters but also those opposed.

The Maryland Marriage Alliance, the group leading the charge to overturn the state’s same-sex marriage law, said that since Obama’s pronouncement — and since leaders of the NAACP followed suit — opponents in Maryland have seen a surge in the number of residents seeking to put gay marriage to a statewide vote.

“When President Obama and the NAACP come out and they wanted to support this issue, well, great, we appreciate that because you help energize our [side],” said Derek McCoy, the group’s executive director.

The alliance on Tuesday filed more than twice the 55,736 signatures needed to qualify the measure for the ballot, and McCoy said the group was on pace to turn in well in excess of its goal of 150,000 signatures by the end of June.

“People that were on the fence are no longer on the fence; they are engaged. . . . Countless thousands of Marylanders around this state want to see marriage go on the ballot. But they also want to see it defined and upheld between one man and one woman,” he said.

Proponents for the state’s same-sex marriage law sought to play down the significance of the number of signatures gathered by opponents. Campaign surrogates for Marylanders for Marriage Equality attended the alliance’s Annapolis news conference. They said the focus should be on recent polling that suggests support is building for upholding Maryland’s same-sex marriage law.

Kevin Nix, a spokesman for Marylanders for Marriage Equality, said his group would not rule out court challenges to the signatures, if merited. But he said supporters of same-sex marriage have always been focused on winning at the ballot in November.

“It’s always been going to happen,” Nix said, referring to opponents’ ability to gather enough signatures to force a referendum.

Maryland’s requirement to petition a law to referendum is relatively low compared with other states’ terms; it is 3 percent of the number of votes cast in the last gubernatorial election.

But petition drives have rarely succeeded in reaching the ballot. With the help of online signature gathering, November will be the first time in 20 years that a petition drive has forced a vote on a Maryland law.

Maryland’s version of the DREAM Act, which would more than halve tuition rates for some undocumented immigrants at the state’s colleges and universities, has qualified for the ballot and withstood all likely legal challenges.

The outcomes of both referendums could reverberate nationally. Maryland will be the only state to weigh in on in-state tuition breaks to undocumented immigrants — a measure that the presumptive Republican presidential nominee, Mitt Romney, has said he strongly opposes.

On same-sex marriage, Maryland could be one of as many as four states that become among the first to confirm gay nuptials by a popular vote, making it a pioneer alongside Massachusetts, the first state in which a legislature legalized same-sex marriage. Same-sex marriage has failed in popular votes in a majority of states.