Proposals for referendums Nov. 6 on the legalization of gambling in the District of Columbia and on construction of the downtown convention center were killed yesterday.

The D.C. Board of Elections and Ethics refused to certify the gambling referendum after receiving a report showing that there apparently were not enough verified signatures of qualified voters on a petition seeking the vote.

A statistical check of 15,917 signatures filed by the gambling backers showed that more than half of the names that had been collected in some parts of the city were invalid. In Ward 8, the far Southeast, 62 percent of the signatures were found to be in error.

Hours later, the D.C. Court of Appeals rejected a last-ditch plea by the Convention Center Referendum Committee seeking to force the elections board to move toward a vote on the financing of the center.

The committee, a citizens group formed two years ago, opposes construction of the center, contending that it would be a money loser and a burden on taxpayers.

Since yesterday was the deadline for the elections board to certify issues for the Nov. 6 ballot, the two actions apparently mean there will be no referendum issues to be decided that day. The election will be limited to candidates for the city school board and advisory neighborhood commissions.

The D.C. City Council itself has power to legalize gambling. However, the council refused earlier this year to take the lesser step of calling an advisory referendum on the issue. That led gambling supporters to circulate their petition which, if successful, would let the voters decide the question in a way that would be binding on the city government.

Elections board chairman James L. Denson, who was joined in yesterday's decision by board member Virginia Moye, said the gambling supporters can continue to collect signatures until January in an attempt to qualify for the ballot next May.

The status of any future referendum on the convenion center was not clear last night, since the Court of Appeals has yet to decide whether the new D.C. initiative, referendum and recall law permits public votes on city-financed construction projects.

The Rev. Ernest Gibson, a leader of Protestant clergymen opposed t- the gambling referendum on moral grounds, grinned braodly when he walked into the elections board's office and heard of the decision. "That is good news," he said, "but certainly it is not the end of the struggle."

Jerry Cooper, vice chairman of the D.C. Committee of Legalized Gambling, which is sponsoring the push for a referendum, glumly acknowledged the board action as seemingly final.

To get an issue onto the ballot, the signatures of 5 percent of the city's registered voters are needed on a petition. The current requirement is 12,451. These must be collected from a cross-section of the city's voters, and not be concentrated in a few neighborhoods.

The gambling supporters filed 15,917 names. However, a sampling conducted by city statisticians showed that the number of valid signatures clearly fell short in Wards 1, 2, 3, 5 and 8 and probably fell short in Ward 4. The numbers were so close in Wards 6 and 7 that they were listed as being "in doubt."

The main reason for rejection, one official said, was that signatures were not those of registered voters.

Upon hearing the report from Mary S. Rodgers, the city's elctions administrator, the board voted to reconsider challenges to the validity of 3,400 signatures or claims of irregularities in the circulation of petitions that had been filed by two groups of clergymen.

One board member, Albert J. Beveridge III, is traveling in China and was not present for yesterday's vote.

The convention center decision by the Court of Appeals ended months of administrative and legal efforts by critics of the project to put its financing up to a public vote.

Congress has appropriated $27 million and is in the process of appropriating another $45 million for the $99 million project, planned at Mount Vernon Square. After seeming at first to put the whole project up for a vote, the referendum committee asked the court yesterday to approve a referendum limited to the final $27 million that eventually would be needed to complete the center.

Superior Court Judge Fred B. Ugast had ruled last week that the elections board had acted correctly in refusing such a referendum.

In a 2-1 decision, after oral arguments, the court upheld Ugast and the elections board.