Some Washingtonians are saying they are glad the tuition-tax credit proposal was defeated, but they wish it hadn't lost so badly.

What they mean is that they had hoped for enough of a "pro" vote to strike a little fear in the hearts of those who run the local school system. They are afraid that the overwhelming rejection of the proposal--it lost badly in every one of the city's 137 precincts-- will be read as a ringing endorsement of the D.C. schools.

There are a couple of things wrong with that assessment. First, since only 8,904 Washingtonians voted for the proposal, nearly twice that number have expressed varying degrees of non- confidence in the most direct fashion: they have taken their children out of the public schools. Second, the problems that plague public education here and elsewhere have nothing to do with the absence of fear in the hearts of school administrators.

What happened Tuesday, I suspect, was more on the order of a ringing endorsement of public education, not of the status quo of the public schools. Opponents of the measure apparently succeeded in driving home the notion that the tax-credit initiative represented an attack on public education.

Perhaps a deliberate attack. Bill Keyes, chairman of the local effort to get the proposal enacted, says all he wanted to do was to provide low-and moderate-income parents with the same public school/private option already enjoyed by the middle class.

I wouldn't debate Keyes' motives. But I do find it significant that several of his supporters, including his campaign manager, Charles Pike, are activists in the Libertarian Party, and the party has made clear its attitude toward public education. Here's what its 1980 platform had to say on the subject:

"We advocate the complete separation of education and State. Government schools lead to the indoctrination of children and interfere with the free choice of individuals. Government ownership, operation, regulation and subsidy of schools and colleges should be ended.

"As an interim measure to encourage the growth of private schools and variety in education, we support tax-credits for tuition and other expenditures related to an individual's education."

The fact that some who supported the measure may desire an end to public education is not to say that all who supported it did so for that reason. I'm willing to take Bill Keyes at his word --that, like Sens. Daniel Moynihan and Robert Packwood and others who favor national tuition-tax-credit legislation, he is motivated by concerns of equity. I quote the Libertarian Party platform simply to point out that some of the support is motivated by more sinister concerns and to caution those who see the issue in less complicated terms.

If the supporters of the measure had mixed motives, so, too, did those who opposed it. Prominent among the opponents, for instance, were the leaders of the teachers' unions, who, while they no doubt are committed to public education, must also have given at least passing thought to the fact that passage of the measure would have jeopardized the employment of a lot of their members.

There's nothing wrong with that, but it is fair to wish that Al Shanker, head of the American Federation of Teachers, and Bill Simons, who heads the Washington Teachers Union, would devote as much enthusiasm to improving public education as they did to defeating the tax-credit proposal.

It is my own opinion that the unions, through their knee-jerk support of their least competent members, are among the forces that have damaged the public schools. So, too, are the administrators who have been reluctant to give honest evaluations to incompetent teachers.

But I wouldn't saddle these two groups with the sole responsibility for the decline in teacher competency. One of the key reasons is the decline in the academic ability of those now entering the teaching profession.

"Put briefly," said Milton Goldberg, acting director of the National Institute of Education, in recent congressional testimony, "the academic ability of education majors is both low and declining, and teaching appears to be attracting the least academically able students."

For instance, he said, between 1972 and 1980, the average verbal scores on the Scholastic Aptitude Test among entering education majors fell from 418 to 339 on a scale of 800. Math SAT scores for aspiring teachers dropped from 449 to 418. Education majors ranked 17th in math ability among 19 fields of study analyzed by the American College Testing Service, 14th in English ability.

What has happened, of course, is that the brighter women are going into other, more lucrative, fields, as sex discrimination declines.

Obviously there are still some outstanding public school teachers, including those who teach my own children. But just as obviously, the overall quality of those entering the teaching profession is plummeting.

In addition, the decline in classroom discipline continues to plague the efforts of even the best teachers. So, too, does the absence of real parental concern for what is happening in the public schools.

It's well enough to be glad that the vote against tuition-tax credits has given the local schools a reprieve. But if we are serious about our commitment to public education, we'd better get busy dealing with these other problems as well.