The D.C. Court of Appeals ordered the city's elections board yesterday to place an educational tax credit initiative on the Nov. 3 ballot, clearing the way for a referendum that supporters and opponents of the measure contend will have immense local and national significance.

Last month, the D.C. Board of Elections and Ethics refused to place the question on the ballot, ruling that more than 82 percent of the 27,000 signatures on petitions calling for the referendum had been gathered improperly.

Yesterday, however, a three-judge panel of the city's highest court reversed that decision and and ordered the board to allow citizens to vote on whether city residents should be permitted local tax credits of up to $1,200 per child for expenses at either public or private schools.

The November vote would mark one of the first referendums in the nation on such a measure. A similar proposal by the National Taxpayers Union failed to get on the ballot in California in 1979.

The three-judge panel -- Frank Q. Nebeker and Stanley S. Harris, with Julia Cooper Mack dissenting -- outlined no reason for its decision, which was expedited because of the nearness of the election. Full opinions will be issued later, the panel said.

The order could be appealed to the full nine-member court, but because the election is less than two months away, that may be impractical, according to some of the opponents.

"We'll be operating in the forum I like best, the election process," said City Council Chairman Arrington Dixon, leader of Save Our City (SOC), an opposition group that includes Mayor Marion Barry and others. "We'll go to the polls to dissuade people from voting for this."

Some national supporters of the plan consider passage in Washington key, in part because the city is predominantly black and such tax-change initiatives are often portrayed as having an adverse impact on blacks.

The proposal's backers, led by William Keyes, a Capitol Hill economist who is black, contend that race would be no factor in the vote here because black parents as well as white ones believe the tax credit proposal would benefit the local schools.

The SOC has focused some of its criticism on the fact that the local sponsoring group, the D.C. Committee for Improved Education, is an offshoot of the National Taxpayers Union, arguing that the proposal is being pushed by outsiders who have come to the District to wreak havoc on the electoral process.

If passed, the measure would drain city revenues and primarily benefit parents with children in private schools, the critics say. Some also think it might be unconstitutional because the government would be used to collect money that could help religious schools.

But supporters of the plan were optimistic after yesterday's court order. "I think we're going to win," said Charles M. Pike Jr., campaign director of the local group. "People are dissatisfied with the existing public education system in D.C., and they're excited that other alternatives are going to be open to them."

The board of elections declared invalid more than 23,000 of the 27,000 signatures after determining that they had been gathered by seven out-of-town residents who were themselves not properly registered voters. The seven moved to town, registered to vote only only in an effort to qualify as petition circulators, and left the city after the signatures were obtained.

Matthew S. Watson, who argued the case before the appeals court on behalf of Dixon and other city officials, said yesterday that the city had been "taken" because it has easy registration processes.

" . . . What's disappointing," Watson said, "is that the city, having tried to keep its franchise open, has really been taken by a very well-organized, single issue group."

Keyes said he felt "jubilation" about the court ruling. "The opponents of our initiative have tried to cloud the issue with all the legal technicalities they could think of, but I was confident we would win," he said.