Two D.C. Court of Appeals judges said yesterday that the city elections board should not have invalidated a proposed Nov. 3 referendum on an educational tax credit simply because some of the petition circulators were found to be ineligible.

Judges Stanley S. Harris, soon to be named by President Reagan as U.S. Attorney here, and Frank Q. Nebeker cited a Board of Elections and Ethics rule saying that signatures of voters who otherwise are qualified should not be invalidated by the failure of the circulator of an initiative petition to be a registered voter.

"The possible sins of the circulator," Harris wrote, "are not to be visited upon the elector who signed petition sheets in good faith."

Harris and Nebeker formed the majority in a 2-to-1 decision issued last month authorizing the referendum. But that ruling has since been suspended by the full court pending a hearing next Tuesday by the entire nine-member panel.

Judge Julia Cooper Mack, the dissenter in last month's decision, said that the initiative's sponsors, a local offshoot of the National Taxpayers Union, had so manipulated the initiative process that it threatened the "integrity of the electoral process." The initiative's sponsors, she said, had engaged in a "pattern of conduct which, in my view, this court cannot afford to ignore." As a result, she said, the elections board was correct in not placing the initiative on the ballot.

Both supporters and opponents of the initiative, which would allow taxpayers to claim a $1,200 tax credit for educational expenses they incur at both private and public schools, consider the issue to have great significance both locally and nationally. The opinions by the three judges, not released until yesterday, will have no immediate effect, but may provide clues to how the entire court eventually will rule.

The initiative has been sharply criticized by city officials who say that if it is approved, it would drain city revenues and primarily benefit parents with chidren in private schools.

The initiative has been following a tortured and uncertain path ever since the elections board originally refused in August to place the question on the ballot.

The board ruled that more than 82 percent of the 27,000 signatures of registered voters on petitions calling for the referendum had been gathered improperly. The board said that 23,000 of the signatures had been gathered by seven out-of-town residents who themselves were not properly registered voters.