YESTERDAY'S WALKOUT by a majority of Washington's public school teachers hardly set a stunning example in civics. The teachers defied a court order and ignored their own signed affidavits forbidding them as public employees to strike. They have acted illegally and must expect to face the consequences. What is at issue that would cause them to behave in this way? The answer is not easy to come by.

Salaries are not directly in this dispute, for they are not a part of the teachers' contracts. They are not even negotiated by the school board. The District council and the Congress handle that -- and therein lies the chief rub. The teachers have no "demands" in the traditional sense this time. They are satisfied to continue working under the terms of their last contract. But after a series of extensions of that contract -- and because Superintendent Vincent E. Reed and a majority of the school board want immediate changes in the teachers' working conditions -- the board unilaterally terminated the contract. The teachers were left with a a board demand for longer work days and school years, and with no salary increases and nothing else that could be classified as a gain. Most teachers found this unacceptable, and walked off the job.

A majority of the board apparently felt that if it took a strike to force another hour's work a day from the teachers and nearly three weeks more a year, so be it. Some people question, of course, how much impact an extra hour a day and other stricter teachers' work rules would actually have on the quality of education. The school board, one has to say, has not yet made the case.

Teacher evaluation procedures are another area of controversy. Stricter standards and tighter monitoring -- which the school board seeks -- must be accompanied by assurances of fairness, incentives for teachers to improve their skills, and effective provisions for monitoring students' progress in each teacher's classes. But until the school board can have the leverage that authority to negotiate salaries provides, it is unrealistic to expect teachers to accept a tightening of procedures governing them agreed to by previous school boards.

That said, there is the immediate need to end the current impasse -- and for that, the city may well look to Mayor Barry. Not only has he demonstrated skill as a negotiator during past teacher-board disputes, but throughout his last campaign Mr. Barry emphasized that he would involve the mayor's office in efforts to help public education in the city, without infringing on the school board's authority. The city government has a stake in ending the strike. A mediation effort by the mayor would be in the public interest.