A Maryland Senate panel voted 7 to 4 on Tuesday in favor of a bill that would legalize same-sex marriage, wasting little time in advancing a measure that narrowly cleared the House of Delegates last week.

With the vote by the Judicial Proceedings Committee, the full Senate is expected to begin debate on the legislation as early as Wednesday and send it to Gov. Martin O’Malley (D) by the end of the week for his promised signature.

A similar bill passed the Senate last year, and opponents sounded increasingly resigned Tuesday to fighting the measure at the ballot box in November. A provision in the Maryland Constitution allows voters to petition just-passed laws to a statewide vote.

“The odds are highly against us in the Senate, I understand,” said Derek McCoy, leader of the Maryland Marriage Alliance, as he made the rounds in a Senate office building, pressing his religious organization’s case against the bill. “But ultimately, the people will decide. In the meantime, the way I look at it, we’ve got to uncover every rock we can.”

The action in the Senate has lacked the drama that unfolded last week in the House, where the outcome remained uncertain until votes were locked in Friday night on the floor.

Last year’s Senate vote was 25 to 21, with one opponent absent. No senators have announced a change in position since then.

“I have no reason to think any votes have shifted against us,” said Sen. Jamie B. Raskin (D-Montgomery), a leading supporter. “We’re at 25 and holding and conceivably could go up one.”

Maryland would join the District and seven states in allowing same-sex marriages. Supporters have cast the bill as a major advance in equal rights. Opponents have called it a misguided attempt to redefine the institution of marriage.

After last year’s bill failed in the House, O’Malley agreed to sponsor it this year.

Opponents of the bill could still attempt a Senate filibuster, which would require 29 votes to cut off. But even they acknowledged Tuesday that such a procedural move is not likely to stop the bill.

Last year, Senate President Thomas V. Mike Miller Jr. (D-Calvert) worked to shut down a filibuster despite his stated personal opposition to the bill.

“They seem to always come up with the number they need to shut us down,” said Sen. Nancy Jacobs (R-Harford), who opposes the legislation.

Another opponent of the bill, Sen. Joseph M. Getty (R-Carroll), said there has been some talk about reaching out to other senators to mount a filibuster in coming days. But, he added, “I wouldn’t say there’s an organized strategy at this point.”

Getty said he expects amendments to be offered on the Senate floor that would strengthen exemptions in the bill intended to accommodate religious groups opposed to same-sex marriage.

Raskin said supporters have gone to great lengths to provide such protections in the bill.

“We have done double somersaults and triple back flips to build religious exemptions into this legislation,” he said.

Supporters are seeking to resist all attempts to alter the legislation in the Senate. If the bill is amended, it must return to the House for additional votes, clouding its chances. Otherwise, once passed, the bill heads straight to the governor.

In part to mock the no-amendments posture of bill supporters, Getty offered an amendment in committee Tuesday that would have moved up the date on which Maryland can start granting same-sex marriage licenses. His proposal was voted down.

If a gay nuptials law is put to voters, both sides expect the outcome to be close. A Washington Post poll last month found that half of Maryland residents favor the legalization of gay marriage but that support varies significantly along the lines of race, religion and age. Overall, the poll found that 50 percent of Marylanders support allowing gay and lesbian couples to marry and that 44 percent are opposed.

Mary Ellen Russell, executive director of the Maryland Catholic Conference, which opposes the legislation, said foes will be “very organized and very galvanized” if the issue goes to referendum.

On Tuesday, however, she was not willing to concede defeat in the Senate. “I’m not by any means thinking it’s likely that we’ll kill the bill in the Senate,” she said, “but that doesn’t mean we won’t keep trying.”