OVER THE WEEKEND -- when there should have been an agreement to end the strike by teachers that has crippled the education of this city's public-school children -- the Washington Teachers Union negotiators arrogantly tossed new, impossible demands on the table. However inept and stubborn the school board may have been initially in refusing to accept Mayor Barry's mediation proposals to end this illegal strike, this move by the union was truly reckless.

Suddenly the union was demanding substantive changes that had no business -- legal or otherwise -- coming up at this time. As most people had come to understand the state of these protracted negotiations during the last two weeks, the teachers originally were striking to preserve the terms of their old contract; salaries were not directly involved, since they are not a part of the teachers' contracts -- nor are they even negotiated by the school board. The school board, having unilaterally terminated the contract, was demanding longer work days and school years. Somewhere in the most anxious middle were the parents and -- lest the warring parties forget -- the children, who have been falling father behind with the passing of each calamitous school day.

So just as the school board had begun to soften its stand by dropping key demands in favor of a back-to-work agreement and negotiations later for a new contract, along comes union president William H. Simons with new demands for everything from a 10 percent pay raise plus cost-of-living increases every three months -- which the board has no authority to act on anyway -- to an absurd proposal under which striking teachers would be allowed to make up their lost pay by working additional days in the spring -- while those who have continued to work would be denied a chance to earn any extra money.

What on earth did Mr. Simons think he was doing by suddenly raising the stakes? Whether it was supposed to be a gesture of confrontation rather than a serious bargaining position doesn't matter -- it wrecked negotiations and guaranteed another chaotic Monday for the students in or out of classes. One can understand the concerns of individual striking teachers about their treatment at work, and one can understand the desires of school board members to improve the quality of teaching. But this war hasn't accomplished a thing for either side. All it has done is play hell with the school year in a system that could ill afford such a setback.