The District of Columbia Court of Appeals advanced the possibility of a voter referendum on the city's proposed downtown convention center yesterday only hours after a City Council committee set back prospects for a similar citywide vote on legalized gambling.

A three-judge appellate panel, overruling a Superior Court decision earlier in the day, ordered the D.C. Board of Elections and Ethics to accept petitions signed by more than 12,000 persons for a May 1 vote that could block spending more than $99 million on the center. The board kept its office open late last night to accept the documents.

The appellate court's action does not necessarily mean an election will be held on the center. The court said in a brief order that it will rule later on that question.

The Board of Elections had said earlier that petitions would have to be filed by yesterday in order to put the convention center question on the ballot of a May 1 special election. A board official said the court's action would preserve the legal rights of the group seeking the vote, the Convention Center Referendum Committee.

The May 1 election was scheduled chiefly to fill two seats on the City Council vacated by the election of Marion Barry as mayor and Arrington L. Dixon as council chairman.

Another, unrelated proposal for a referendum was dealt a potentially fatal blow at a meeting of the City Council's government operations committee. The proposal called for a vote on creating a city-run lottery and legalizing off track horse betting here.

Before an audience that included dozens of ministers opposed to the gambling proposal, three of the committee's five members declared themselves firmly opposed to putting it on the ballot.

But one of the three -- William R. Spaulding (D-Ward 5), chairman of the committee -- postponed a formal committee vote until its next meeting Feb. 14, at the request, he said, of Council Chairman Dixon and David A. Clarke (D-Ward 1), sponsors of the gambling measure.

Dixon had other appointments yesterday and could not attend the meeting to speak for the proposal. Clarke was out of the city.

The Rev. Raymond Robinson, pastor of the Israel Baptist Church and chairman of the Committee of 100 Ministers, which is spearheading opposition to the gambling proposal, voiced dismay at the postponement. He said he feared that progambling lobbying in the next two weeks might alter the committee lineup.

Spaulding, Nadine P. Winter (D-Ward 6) and Jerry A. Moore Jr. (R-At Large) said they would stand firm against the gambling plan. Betty Ann Kane (D-At Large) and Hilda Mason (Statehood-At Large) said they favor the referendum process, but Mason said she might vote against the referendum because of the proposal's wording.

The referendum would carry out a recommendation made last year by a citizens' gambling commission, which said its proposals would bring at least $40 million a year in revenue to the city.

The only witness yesterday against the proposal, the Rev. John D. McArthur of the Metropolitan Wesley AME Zion Church, speaking for the Committee of 100 Ministers, attacked the idea of government involvement in gambling.

"The poor elements of our community will be caught in the gambling net," McArthur testified. "I hope and pray that our government will never stoop to that level."

The city's Home Rule Charter gives the council power to put advisory referendums on the ballot. There is no clear power yet for the general public to bring about a referendum to enact a law or to invalidate a law passed by the City Council. That is what the convention center lawsuit is all about.

District citizens voted in 1977 to create a citizen-initiated referendum procedure, but the City Council never passed legislation to establish the machinery for implementing the idea.

That posed a problem for opponents of the convention center, which was approved by the council and Congress for a site near Mount Vernon Square. The project has strong support from city planners, business groups and organized labor.

Failing to get the Board of Elections to accept petitions for a May 1 referendujm on the project, the project's critics appealed to the courts. Superior Court Judge Norma Holloway Johnson turned them down yesterday. They immediately to the Court of Appeals, which issued its order to the elections board.

At its meeting yesterday, the council's government operations committee voted its approval for a bill creating the machinery for public referendums. It must still be considered by the full council.