Supporters of a citizen's initiative to grant District of Columbia resident tuition tax credits of up to $1,200 per child have submitted 27,415 signatures of registered voters to city election officials, nearly twice the number required to place the measure on the ballot.

But the D.C. Board of Elections and Ethics was unable to decide yesterday whether the measure is constitutional, and thus able to be placed on the November ballot. The board's legal counsel, William Lewis, told board members he believes the measure is unconstitutional because it would greatly benefit Catholic or other religious schools, violating the separation of church and state.

Similar tax credit proposals have generated heated and often bitter debates in other parts of the country, with proponents arguing that they merely want to give parents a choice in the education of their children and opponents contending that the tax credits would mean the death of public education.

The proposal would allow any District taxpayer to take a credit of up to $1,200 per school-age child. The credit would go toward "educational expenses," whether it is used in private schools for tuition or in public schools to provide more services. Corporations and individuals who do not have children could also use the credit, in effect giving some students a private school scholarship or giving the public schools operating funds.

The plan's supporters acknowledged that they relied on some help from Catholic school parents' groups collecting their signatures. The 27,415 is the largest number or petition signatures ever gathered for a D.C. initiative. If the board decides to allow the measure to proceed, it will then have to verify the signatures. A total of 14,442 names of registered voters are required to place the initiative on the ballot.

Such proposals elsewhere have been attacked as subsidies for upper-income parents who want to send their children to private schools. But backers of the D.C. initiative say that is not their intention.

"There's one fundamental thing that people don't seem to understand," said economist Bill Keyes, chairman of the D.C. Committee for Improved Education, which is sponsoring the initiative. "Everyone thinks that this is to help private schools and upper-income people. But it's low-income people who are most excited about this, because they see a way their kids can be a little better off [by attending private schools]."

But elections board lawyer Lewis argued at the board meeting yesterday that the measure is unconstitutional, because it would have the obvious effect of aiding Catholic and other religious schools.

Lawyer H. Richard Mayberry, representing the sponsors of the plan, was joined by the American Civil Liberties Union in arguing that the board should allow District voters to decide on the proposal, and then let the courts decide the issue of constitutionality.

Elections board chairman Albert J. Beveridge III said the board would decide by Monday whether to go ahead and review the validity of the signatures.