Maryland Gov. Martin O’Malley said Friday that supporters of same-sex marriage will have to work hard to pick up additional votes next year, and he confirmed plans to put the full weight of his office behind the effort to pass a bill.

O’Malley (D), a Catholic who until recently advocated civil unions as an alternative, said at a news conference in Annapolis that legislation to legalize same-sex marriage would be “one of the handful of bills” that he’ll sponsor when the General Assembly convenes in January.

“At the end of the day, I think all of us need to look at this issue from the eyes of children of gay, committed couples and ask ourselves how one family could be protected less in the eyes of the law than another family,” O’Malley said, flanked by lawmakers who support the legislation. “I don’t think that’s an injustice that can be allowed to stand.”

A same-sex marriage bill narrowly passed the Maryland Senate during this year’s session but fell short in the House of Delegates. O’Malley had pledged to sign the bill if it reached his desk, but his efforts to get it there were largely confined to private conversations with lawmakers.

Particularly since this month’s passage of a same-sex marriage bill in New York, gay lawmakers and other supporters in Maryland have urged O’Malley to play a more visible role. New York Gov. Andrew M. Cuomo, another Democrat whose national profile is rising, was widely credited with pushing the legislation through a divided legislature in his state.

While O’Malley’s announcement was heartily applauded by gay rights advocates, bill supporters acknowledged that they have not yet secured additional votes since the session ended in April. By most accounts, the bill was at least two votes shy of passage in the House, where a vote was not called in the full chamber.

The legislation ran into stiff opposition from black churches in Prince George’s County and proved a tough sell with Democratic delegates from more-conservative areas of the state, including Southern Maryland and the Baltimore suburbs.

“When you’re one or two votes short, clearly a push from a very popular governor can do nothing but help,” said Del. Justin D. Ross (D-Prince George’s), part of a team of lawmakers responsible for rounding up votes in the House.

Ross, who supports same-sex marriage legislation, said O’Malley’s decision to get more involved was “not born of a confidence that it’s a done deal. It’s born of a confidence that it’s the right thing to do.”

When pressed by reporters, O’Malley shared little about the evolution in his personal thinking. “I have always believed in the dignity of every individual,” he said shortly before aides ended the questioning. “I believe in our own responsibility to advance the greater good . . . and that what we do in our own lifetimes does matter.”

Earlier, O’Malley noted that he was a product of Catholic schools and said “raised to understand that there are things that churches and religions dispense, and that government should not interfere in defining those.”

He said, however, that the bill in New York showed that there is a way to balance the protection of religion with the advancement of equal rights. In coming months, he said, his office will examine whether additional religious exemptions should be added to the Maryland bill.

“We still have a lot of work to do,” O’Malley said, saying the news conference was intended “to commit ourselves to that work.”

Opponents of the legislation were quick to criticize O’Malley. The Maryland Catholic Conference released a statement calling the governor’s decision “regrettable.”

“Gay marriage failed in Maryland earlier this year because the House of Delegates listened to their constituents,” the Maryland Family Alliance said in a statement. “Maryland is not New York.”

While O’Malley typically wins more legislative battles than he loses, his sponsorship of a bill is hardly a guarantee of success. He has fallen short in persuading lawmakers to repeal the death penalty and to pass legislation intended to jump-start the state’s wind-energy industry.