The D.C. Board of Elections and Ethics yesterday gave preliminary approval to a November referendum that would allow voters to decide if city residents can claim educational tax credits of up to $1,200 per pupil for expenses at either private or public schools.

The approval is still subject to a spot-check verification of the 27,415 signatures on petitions for the referendum -- almost twice the required number -- and was made over objections from the board's lawyer.

Board member Virginia Moye, who announced the unanimous decision of the three-member panel, said she thought the proposal probably was unconstitutional because it would aid church schools.

But, Moye explained, "We don't feel the (elections) board has the prerogative to make that decision. It isn't cut and dried . . . I think it's up to the courts to decide whether it is constitutional."

At a meeting last Wednesday, general counsel William Lewis urged the board to keep the proposition off the ballot because he said it violates the federal constitutional requirement for separation of church and state.

But sponsors of the plan, the D.C. Committee for Improved Education, argued that the board should not substitute its judgment for that of the voters. The American Civil Liberties Union also urged that the board allow voters to decide, and then let the plan be subject to court challenge if it is approved.

Under the proposal, taxpayers would be eligible for a credit of up to $1,200 per pupil for all expenses paid for D.C. children in kindergarten through 12th grade attending "public or private schools which maintain racially nondiscriminatroy policies." The credit would be less for families earning below $20,000 a year -- the level at which $1,200 in taxes are due. But non-parents who helped pay for these children's education could get the same credit as long as the total tax credit per child did not exceed $1,200.

The eligible expenses would include tuition, books and various fees at private and parochial schools located in Washington or outside the city and fees paid for supplemental services at D.C. public schools. These services might include kindergarten aides and special math, reading or music programs.

The committee that gathered the petitions here is an offshoot of the National Taxpayers Union, which mounted an unsuccessful statewide petition drive for a similar proposal last year in California.

Bills for a simple private school tuition credit on federal taxes have been introduced in Congress and supported by the Reagan administration. They have been bitterly assailed by a wide array of liberal, labor and public school groups.

If the local effort withstands the signature check, which must be completed by Aug. 6, it would appear on the ballot at the same time that six seats on the school board are to be filled and delegates chosen to a constitutional convention on D.C. statehood.

Bill Keyes, chairman of the referendum drive which collected almost double the required 14,442 signatures, said he was overjoyed by the board's decision.

Keyes said he was certain that enough signatures would be verified to get the proposition on the ballot, where he predicted it would get wide support from low-income parents who now feel "trapped in a system where they have little or no ability to influence decisions."

In a statement yesterday afternoon, Mayor Marion Barry repeated his view that the proposal would "undermine public education," and promised that "I will do all I can" to defeat it.

Keyes responded by noting that under the plan the money could be spent for supplemental programs at public schools as well as for private school fees, and said its main effect would be to reduce the power of public school officials.

"The point is control," Keyes said, "whether or not they [school officials] have a lock on the decision-making about the education of our children or whether we have some leverage."

A simple majority of those voting on the proposal would be necessary for the measure to pass.