In 2004, 19 people filed a lawsuit seeking to overturn the 1973 statute that defines marriage as the union of a man and a woman. Maryland's highest court denied the claim in 2007.
More recently, lawmakers voted to provide hospital visitation rights to gay couples and exempt some property transfer taxes for domestic partners.
Democratic Attorney General Douglas F. Gansler issued an opinion last year that the state should recognize same-sex marriages performed in jurisdictions where it is legal. Though opponents of gay marriage criticized his conclusion, Republicans did not field a candidate against him in November.
Equality Maryland, the state's most visible gay advocacy organization, took an active role in the campaign last year, appealing to Democratic candidates to declare their positions on same-sex marriage.
During the Senate debate, Equality Maryland advocates delivered Valentine's Day carnations to lawmakers. Their hope: that Maryland would follow the neighboring District of Columbia, which began issuing marriage licenses to gay couples last year.
Five states now recognize same-sex marriage, and efforts are on the move in New York and Rhode Island. Hawaii and Illinois recently approved civil unions, which are contracts between any two adults.
Gay Marylanders who watched the legislation's failure in the House said they were not giving up.
"Obviously we just need to fight harder," Jenny McAtee said.
Earlier, McAtee had embraced her partner, Julie Mason.
"This is my wife," Mason said, "and I'd like the state to recognize that."
Gov. Martin O'Malley had pledged to sign the bill if it reached his desk, but began reaching out to lawmakers only in the days before the vote. First lady Katie O'Malley also quietly pushed the issue.
The Democratic governor made calls to undecided delegates, appealing to them as a Catholic. According to a spokesman, O'Malley told delegates that it wasn't an issue of faith, but of equality.
House Speaker Michael E. Busch, also Catholic, met continually with delegates the past week.
The timing proved wrong this year. The 30 newly elected delegates were still moving into their offices in January when they were asked to sponsor legislation that even more senior members didn't fully grasp.
Freshman Dels. Tiffany Alston and Sam Arora both enthusiastically backed the bill at the beginning of the session. Both withdrew their support — Alston, after constituents and her church made their opposition clear, and Arora for religious reasons that he has not explained.
Del. Melvin Stukes said he sponsored the bill, titled the Civil Marriage Protection Act, only because he believed it was a civil unions plan. Records show the Baltimore Democrat has sponsored similarly titled gay marriage legislation three previous times.
As the details of the legislation became apparent, Stukes withdrew his support.
Busch said legislators — and the public — need more time to understand the arguments for gay marriage, and why it is superior to civil unions.
"There has not been enough of an education process," Busch said. "I think you need another year and more information."
Some gay marriage opponents who watched the debate Friday said they felt misunderstood.
"It's hard to be painted as haters, it really is," said Martha Schaerr, a Montgomery County resident. "The commitment to traditional marriage doesn't mean we hate gays. The line that I can't cross is marriage."
Busch, who supports gay marriage, and Senate President Thomas V. Mike Miller, who does not, say the General Assembly could take up the same-sex marriage issue again next year. With the Senate's approval on record, next year's legislation would start in the House.
Some say it will take another election, and a new General Assembly, to get a different result. Lawmakers don't face re-election until 2014.
"They would be foolish to try again next year," said Del. Don H. Dwyer, an opponent of gay marriage and Anne Arundel County Republican. "But if they do, we'll be ready."
Advocates hadn't thought they would need a legislative strategy for 2012, after the Senate voted 25-21 to approve the bill. The Senate has long been considered more conservative than the House.
For supporters, the signs were all positive. Sen. James Brochin, a Baltimore County Democrat who had campaigned against same-sex marriage, became a supporter after being put off by vitriolic remarks by opponents. He was joined by a Republican, Sen. Allan H. Kittleman, who had stepped down as minority leader over the issue.
Sen. Jamie Raskin, a Montgomery County Democrat, sees evidence of a larger philosophical shift in the legislature.
The Senate gained two Democrats last fall as the House lost six. On Monday, the upper chamber is expected to approve a bill that would allow illegal immigrants to qualify for in-state tuition at the state's public colleges and universities. The House hasn't given even preliminary committee approval to the measure this year.
"It may be," Raskin said, "that we are moving into a period of the Senate being the more progressive body."
Baltimore Sun reporter Yeganeh June Torbati contributed to this article.
