THE SCHOOL BOARD and the teachers are operating under a 90-day contract extension that expires in January. The negotiations deserve attention not merely because of the possibility of a strike, but because they involve conditions in the classrooms, from the quality of teaching to the number of children in each class.

Since salaries are not part of the contract (they are handled by the mayor and city council), the board and the teachers are talking about changes in the schools. For example, the teachers union is seeking new limits on class sizes, more and better classroom supplies and textbooks and new restrictions on the operation of "open space" classrooms. Parents whose children have wound up in classes of 39 to 45 students for one teacher - or in "open" situations with twice as many students and maybe two teachers - can readily recognize the importance of this proposal. Good teachers are being frustrated by the fact that they cannot do their best for the students under current classroom conditions.

The school board wants longer school days and school years for the teachers. It proposes that teachers work an extra hour every day, for a 7-hour day plus a one-hour lunch period; and that they work an extra 14 school-days each year.That amounts to a pay cut, which the union is unwilling to accept. So there is little likelihood that this matter can be entirely settled in a contract that doesn't deal with salaries. Besides, going to war over an extra work beyond their required hours. Arguments can be made for a slightly longer school year, however: The District's is among the shortest in the country.

But what about the quality of teaching? The school board wants to remove teacher-evaluation procedures from contract negotiations to allow for tougher, unilateral evaluation standards. The union agrees that incompetent teachers should be fired, but argues that procedures ensuring fairness must be part of a working agreement. Instead of insisting on eliminating contractual protections, the board should focus on proposals for regular testing of teachers, incentives for teachers to improve their skills and agreement on fair ways to monitor student progress in each teacher's classes.