ONCE IN WHILE a bill comes along that is so thoroughly bad that most legislators who support it come to regret their vote. Such a bill is the Department of Education plan now nearing crucial votes in the House. If the House does agree to enshrine an unsulated, supergraded federal educational bureaucracy in the Cabinet, the results are likely to be so costly and unhealthy for American education that many representatives, in retrospect, will be embarrassed to admit they voted "yea."

For one perspective on what is wrong with this idea, consider the nature of it interest-group support. The bill would mainly amputate Education from Health and Welfare and elevate it to Cabinet rank. You might expect that the strongest backers of this idea would be those educational practitioners, promoters and purveyors who stand to benefit most directly from the new department's additional prestige and managerial autonomy - not to mention the larger budgets that its secretary and 90 top-level executives would lobby for. And that's the case. This whole project is backed most loudly by people in the education business - plus some civil-rights groups beguiled by the prospect of gaining, yes, an autonomous Office of Civil Rights.

But iths not backed by all of them. The American Federation of Teachers opposes the department. So do several organizations representing Catholic education. So do spokesmen for a bevy of private colleges and universities. Why do they object? In various ways, they fear that the department would not benefit them - that it is likely to be all too responsive to a rival union, to certain kinds and levels of education. In short, they fear that it would not reflect, recognize or promote the full diversity and richness of American education in its broadest, most basic sense.

That concern is not just hypothetical; it has a good, explicit cause. The primary force behind the bill is the National Education Association, which sold the idea to Jimmy Carter during the 1976 campaign and persuaded many House members and candidates to endorse the concept before they had any reason to weigh it seriously. And if you worry about the potential for arbitrariness and overreaching that a department embracing all of education would possess, you should be even more wary of setting up a multi-billion-dollar grant-and-contract-dispensing agency that is so likely to become the preserve of any one highpowered, rigidly focused group.

Nothing in bureaucratic experience suggests that it would turn out any other way. Look at the problems of weaning the Commerce Department away from its single-purpose constituency. Look at Labor. Better yet, look at two narrower and much more exploitative arrangements - the old Post Office Department and the maritime agencies, with their all-too-cozy ties and mutually supportive alliances with interest groups and friendly congressional committees. That is the real model that House members should keep in mind. Some congressman who have made casual commitments to the administration or the NEA may find it slightly awkward to back away. But a vote for this regressive, regrettable bill would be much more embarrassing - and impossible to retrieve.