The Maryland House of Delegates effectively killed a measure Friday that would legalize same-sex marriage in the state — halting momentum in a year in which proponents thought they would prevail.

Just two weeks ago, it appeared the bill could sail to the governor’s desk. Supporters were optimistic after the legislation cleared the Senate, generally considered the state’s more conservative chamber.

Objections to the speed at which the measure was being considered and opposition from the constituents of some wavering members led the House on Friday to return the bill to committee, a tacit acknowledgment that it lacked enough votes to pass during this year’s session.

Despite pleas from gay colleagues Friday, the General Assembly, which will end its 90-day session in early April, won’t consider the measure again before January at the earliest.

“The Senate vote was definitely a wake-up call,” said Minority Leader Nancy C. Jacobs (R-Harford). “It got the churches involved. It got people involved. Quite frankly, I thought it was going to fly through the House. But once delegates started hearing from their constituents, they started thinking twice.”

The bill had been a tough sell among African American lawmakers from Prince George’s County, who cited religious opposition in their districts, as well as conservative Democrats in Southern Maryland and the Baltimore suburbs.

But some delegates said they were surprised by the strength of the opposition in their home districts. Others, particularly new members of the House, said they need more time to weigh the issues of civil rights and religion.

“I’m taking the courageous stance,” said Del. C.T. Wilson (D-Charles), one of several members who said during debate that he would not bend to pressure to vote for the bill. “I have not had a chance to take this to my constituents and get their opinion,” he said.

House leaders said they remained one or two votes shy of a majority but predicted that the outcome could be different next year after lawmakers, particularly the chamber’s 30 freshmen, have more time to consider the matter.

“I fully expect to see a bill come in front of the Maryland House of Delegates next year,” House Speaker Michael E. Busch (D-Anne Arundel) told reporters after Friday’s session. “This is a distance run, not a sprint. . . . We never asked anyone to support this bill unless they felt comfortable with it.”

Gov. Martin O’Malley (D), who had lobbied some delegates behind the scenes but not played a very visible role in recent weeks, said he was “disappointed” by Friday’s action.

“I would have hoped that we could have resolved this issue and then let the people decide,” he said, referring to the likelihood that opponents would have petitioned the issue to the ballot.

The Maryland Constitution allows citizens to force public votes on newly passed legislation if they collect enough signatures. A successful petition drive would have put the same-sex marriage measure on hold pending the outcome of a statewide vote in November 2012.

Several delegates who spoke against the bill during Friday’s debate said they wanted a way to guarantee that the public would vote.

“The voters should have a right to weigh in on this issue,” said Del. Aisha N. Braveboy (D-Prince George’s). “I don’t know who’s right, and I don’t know who’s wrong.”

For months, the conventional wisdom in Annapolis had been that the Senate would be the difficult chamber for advocates of same-sex marriage.

Equality Maryland, the state’s leading gay-rights organization, and other advocates focused much of their attention on the chamber, orchestrating calls and visits from senators’ constituents who favored the legislation.

Until days ago, House supporters of same-sex marriage continued to express confidence in the bill’s prospects. The reality is the chamber is not quite as liberal as it used to be. Although Democrats picked up two seats in the Senate in November — bucking a national trend — they lost six in the House.

Del. Anne R. Kaiser (D-Montgomery), an openly gay lawmaker, said five of the six Democrats who had held the seats lost to Republicans were supporters of same-sex marriage.

House leaders said they were also taken aback by several delegates who co-sponsored the bill — usually a strong signal of support — but then started to express doubts.

The most visible of those was Del. Tiffany T. Alston (D-Prince George’s), one of 59 members whose names appeared on the bill as sponsors or co-sponsors.

The first sign that the legislation was in trouble came early last week when Alston and another delegate skipped a Judiciary Committee voting session, postponing the bill’s consideration for several days.

The measure was sprung from committee last Friday only after its chairman, who rarely votes, cast a deciding tally.

Alston, who didn’t speak during the floor debate, had said she was flooded with calls and e-mails from church-going constituents and others saying they didn’t support the bill.

Other delegates whom House leaders thought were on board — or would get on board — started expressing reservations as well.

Busch had fewer options at his disposal than on most issues. Early in the session, he made clear that he considered same-sex marriage a “conscience” vote, meaning House leaders would not pressure members to vote with the Democratic majority.

As a result, the normal “whip” operation that builds support for bills was not operating. Majority Whip Talmadge Branch (D-Baltimore), whose job it is to round up votes on other issues, opposed the measure.

Branch said his position reflected that of several prominent Baptist churches in his district that are an important part of his political base.

Several other members of the House leadership, who usually vote on bills the speaker supports, also opposed the same-sex marriage legislation.

After a week-long series of conversations with wavering members, Busch and other advocates of the measure concluded Thursday night that they were unlikely to get the necessary votes.

Busch said Friday that sending the bill back to committee without a recorded vote could make it easier for some members to vote in favor of the measure next year — in effect, they would not be changing their position.

Even though there was little chance of the measure’s passage Friday, there was plenty of passion from both sides.

Del. Benjamin S. Barnes (D-Prince George’s), a leading proponent of the legislation, argued that Maryland is discriminating against gay couples by not allowing them to marry.

“Injustice is injustice,” he said. “We have a duty in this chamber to stamp it out.”

Del. Luke H. Clippinger (D-Baltimore), one of seven openly gay House members, pleaded with his colleagues. “Today I ask you for your vote to make me a whole citizen of this state,” he said.

Meanwhile, opponents urged their colleagues to keep the traditional definition of marriage.

Del. Steven R. Schuh (R-Anne Arundel) said the state should provide incentives only for those unions between “the unique combination of human beings that brings new life into the world.”

House leaders said no Republicans seemed likely to vote for the bill.

Outside the state House, about 30 protesters of the bill, most members of a traditional family-values group from Pennsylvania, erupted into shouts of “Hallelujah” and “Praise the Lord” as lawmakers emerged with the news.

“We won, we won,” said Del. Joseph J. Minnick (D-Baltimore County) as he thrust a thumbs-up sign to the gathering. “You can thank that man,” he said pointing to Del. Emmett C. Burns Jr. (D-Baltimore County), who had blasted the legislation during Friday’s 21/2 -hour debate.

Burns approached several women carrying Bibles and placards, embraced one and then hurried toward his office.

Across the street, an equally small group of proponents of the measure continued cheering with each passing car that honked, seemingly unaware of the decision reached inside.

Staff writer Aaron C. Davis contributed to this report.