If Washington voters approve an educational tax credit initiative on the Nov. 3 ballot, city parents will find it easier to pay the bills for children in private schools -- but almost everything else about the five-page measure is subject to sharp debate.

To its proponents, a local off-shoot of the National Taxpayers Union, the tax credit would promote school choice and competition. It would help low-income children escape from bad public schools, they say, and perhaps goad the public schools to improve.

To its foes, who include most city leaders and a broad coalition of civic, labor and religious organizations, the credit, which would reduce the D.C. income taxes of those who take it, is a "soak-the-poor-to-give-even-more-to-the-rich proposition," in the words of school board member R. Calvin Lockridge (Ward 8). The measure would drain large sums from the city treasury, the opponents say, and hurt the public schools and the low-income children who have to attend them.

More than 27,000 voters -- almost twice the required number -- signed petitions to put the measure on the Nov. 3 ballot. But exactly what it might do -- even the meaning of the ballot language that limits the credit to $1,200 per pupil -- is sharply contested.

"This is a grand experiment and no one knows how people will behave," says Leslie Harris, a tax credit foe who is executive director of the American Civil Liberties Union of the Washington area.

Bill Keyes, chairman of the D.C. Committee for Improved Education, the sponsor of the proposal, agrees. "You can't have all the answers to all the questions right now," he says. But Keyes adds quickly that the city and its school children will be better off with the tax credit than without it, a contention that Harris sharply disputes.

What voters will see on the ballot is an 87-word summary prepared by the D.C. Board of Elections and Ethics. What they will put into effect, if it survives a review by Congress and probably a challenge in court, is a five-page law.

A few points in the proposed law are clear:

* No matter how strict the tax credit's limit, the measure says that amount will go up automatically 10 percent a year or, if the City Council approves, by a percentage equal to the rate of inflation.

* Also, the money can be spent for any students who are legal residents of the District of Columbia no matter where they go to school. D.C. City Council member Betty Ann Kane (D-At Large) suggests it might be used for boarding schools in Switzerland. Yes, that is possible, says Keyes, but more likely the money might be spent to send city children to unfilled suburban classrooms -- a development, he says, that would promote desegregation.

* According to the ballot summary, the credit can be used by taxpayers for the "educational expenses" of full-time students at "public or private schools which maintain racially non-discriminatory policies."

But the two sides disagree strongly about what the "educational expenses" might be and how much could be spent in public schools -- a dispute that probably will be settled through administrative regulations or court decisions if the measure becomes law.

Here are some of the major questions and answers about the proposal:

What is an educational tax credit?

A credit gives taxpayers a dollar-for-dollar reduction in the amount of taxes they owe. In this case the reduction would be in D.C. income taxes from both individuals and corporations, parents and non-parents as long as they have used the money for "qualified educational expenses" of D.C. students.

What level of school would it be good for?

Kindergarten through 12th grade.

The proposed credit could not be used for nursery schools and day care centers, which already qualify in a much more modest way, for child-care credits on both federal and D.C. income taxes. It also could not be used for colleges.

How large could the proposed D.C. credit be?

The limit, according to the measure's proponents and the ballot summary, is $1,200 per pupil next year with annual 10 percent or cost-of-living increases after that. But the opponents say there is, in effect, no limit because of a phrase in the text which reads, "the maximum dollar amount allowable to the taxpayer as a tax credit . . . shall not exceed $1,200 for each eligible pupil."

Under this provision, says the D.C. Coalition for Public Education, an anticredit group, the same child could benefit from any number of parents, grandparents, or corporate benefactors, so long as no one taxpayer spent more than $1,200 per child.

The same charge was made in July by a group of city officials, who sought to keep the proposal off the ballot. But the Board of Elections rejected its contention, ruling 2 to 1 that the summary, which says the limit is $1,200 per pupil, was not inconsistent with the text or misleading.

"If the proponents say they intend it to be $1,200 per pupil from all sources , who am I to say they haven't done it?" said Albert J. Beveridge III, the elections board chairman. "The specific statute is hardly clear. But I don't think they're trying to pull a fast one."

If the measure passes and there is still a dispute, said Beveridge, "It certainly could be clarified by the City Council, just as last year's D.C. statehood initiative was. I'm sure it would be, knowing how much the council dislikes the whole thing and wants to limit the loss of revenue."

How much could the credit help public schools?

A great deal, say the tax credit proponents. The eligible expenses not only would include tuition, books, and fees at private and parochial schools, but also money contributed for supplemental services at D.C. public schools. These might include kindergarten aides, and special math, reading, or music programs for which parents at some D.C. schools already raise money, according to the proponents.

The opponents say very little tax credit money could go to public schools because, according to the text, the money must be used "for fees actually charged . . . and incidental expenses incurred for and in connection with" attending a school.

George Margolies, legal counsel to the D.C. public school administration, said the measure limits public school credits to yearbooks, sports equipment, bus tokens, and other minor expenses. But Jule Herbert Jr., executive director of the National Taxpayers Legal Fund and chief drafter of the measure, said "incidental expenses" means anything that is "naturally attendant" to schooling and has a wide range.

Both sides say the disagreement could eventually be settled by regulations of the D.C. finance department, and if there still is a dispute, by a lawsuit.

What kind of students would benefit from the increased aid to private schools?

According to figures compiled by the D.C. Board of Education, 53 percent of the 20,197 D.C. students attending private schools last year were black. In D.C. public schools, blacks made up 95 percent of the almost 100,000 enrollment.

No complete data is available on the family income of either group, though last year, 58 percent of the public school students were poor enough to get a free or reduced price lunch.

Nationwide, Census Bureau data show a larger proportion of high-income children in private schools than in public ones, but Catholic schools, which account for slightly less than half of Washington's private school students, enroll substantial numbers of low-income youngsters.

Could low-income children benefit from the tax credits?

Under the proposal, the credit would be less than its maximum $1,200 for families earning less than $21,500 a year -- the level at which a family of four and taking the standard deduction would owe $1,200 in D.C. income taxes.

Tax-credit proponents say nonparents or wealthy taxpayers or corporations could help pay for these children's education because they could take the credit, too, though for corporations it is limited to 50 percent of D.C. taxes.

As a practical matter, opponents say few such donations would be made, particularly since donors who itemize would have to pay higher federal income taxes if their city tax bill was cut.