FLORETTA D. McKENZIE, superintendent of the Washington school system, took to the podium of a recent League of Women Voters meeting to campaign against the school tax credit proposal that will appear on the ballot Tuesday. The proposal, which would allow a $1,200-per-pupil D.C. income tax credit for expenses at either public or private schools, has been attacked as a drain on the city's treasury and a threat to the public schools. McKenzie raised the question to even loftier heights:

Saying she felt like a "prime minister needing a vote of confidence," she told her audience: "Give public education a vote of confidence for the whole nation to see."

But the issue is not, as the opponents of the tax credit would have voters believe, whether Americans believe in public education. Public education that will enable the citizenry to reason through the complicated questions of government and society is intrinsic to a democracy, and Americans have had a longstanding commitment to it. The issue is public education in Washington.

Were the city's schools educating its children, there would be no call for a tax credit. But the state of public education in Washington is shameful. For years the schools have been plagued by discipline problems. The system has been repeatedly disrupted and embarrassed by its leadership. Only last year did the schools reinstitute a policy of holding back children who were not prepared for the next level.

The cost has been tragic to generations of children. One-seventh of the children from grades one through three failed to meet promotion standards last June. The SAT scores of older students -- scores chiefly designed to measure reasoning ability -- have averaged 200 points below the average for the United States and 250 points below the average for Washington's suburbs. One-fourth of the older teen-agers can't get jobs. How did the parents let the education of their children come to such a state?

Part of the answer is that parents of nearly 17,000 children have put their children in private schools. And it has cost a lot of money -- up to $4,300 in tuition per child. At the same time that these parents are forking over tuition to ensure that their kids can read and write and have some acquaintance with the fundamentals of reasoning, they are subsidizing a system that has proved itself largely incapable of doing the same for children who can't get out of it. Is it any wonder that a movement to help the schools that are doing the job should arise?

The wonder is that something of this sort hasn't happened before. The wonder of it is that parents who have children who can't get out of the schools haven't taken to the classrooms and the auditoriums and the school board offices to demand discipline in the classes and teachers who can teach. The wonder of it is that they aren't demanding that their kids get enough homework so they can learn.

In a recent column in The Washington Post, Jessica Tuchman Matthews cited national statistics that ought to raise the hair of anyone wondering how we are educating our youth: 75 percent of last year's graduating seniors throughout the nation reported spending less than five hours a week on homework, while 26 percent of them reported spending more than four hours a day watching television. This is a city whose students fall hundreds of points below the national average. What would the figures be here? And what are the parents doing about it?

The tax credit issue has set people thinking about public schools here in a way that hasn't happened in years. Hundreds of thousands of dollars are being spent by both sides in the debate. The Board of Trade, which rarely takes a stand on such issues, has come out against it. Suburban school superintendents, buying the argument that public education as a whole is threatened, have joined in an unprecendented show of unity with D.C. officials.

That a tax credit proposal is on the ballot is a measure of how confidence in Washington's public education has eroded. The school board, the superintendent, the teachers and bureaucrats who run the schools and the politicians who control the budget ought to be shaking. The parents ought to be taking a hard look at what they are doing: Are they backing up the schools when it comes to discipline? Are they going to PTA meetings and back-to-school nights and attending parent-teacher conferences and taking away privileges when poor report cards come home? And are they going to vote in school board elections for people who will support the educational consensus that seems to be emerging from the superintendent's office rather than for people who will disrupt it?

The tax credit proposal has provided a healthy jolt to a system that has done such a negligent job of preparing its young people for the responsibilities of citizenship. If the initiative should fail, the most tragic outcome of all would be for those who are responsible for good public education here to celebrate it as a vote of confidence in the job they are doing.