LABOR DAY, and not a moment too soon. If you lament the passing of this summer, you didn't spend it in Washington. It's been a season of brutal temperatures, not enough rain, dispirited politics and a truncated Olympics. The valiant survivors of this summer are now making their way to the end of it like a band of travelers straggling across the Sahara. Cheer up; it's almost over.

The rhythm of American life changes at Labor Day. It's the beginning of a new school year, and school is, after all, the central American enterprise, engaging more of this country's people than any other. Labor Day sends well over one-fourth of the country's population back to the classroom -- 61 million of us, students and teachers, from kindergarten to graduate school.

Americans have always believed that the perpetualtion of their particular idea of civilization depends on their schools, and they are right about that. There is nothing that Americans quarrel about more productively than education. Everyone in this country over the age of 12 criticizes the schools' curriculm, objects to the current trends in teaching methods and knows that standards are declining. Those convictions go with citizenship, like a passport. But a couple of new books under a kid's arm are a sign of private progress that everybody knows is real. For a couple of weeks, teachers will complain about these hot, stuffy, non-air-conditioned classrooms. Then the temperature will at least drop a little, and the serious time of year will begin.

Fat and glossy is the tomato, not to mention the eggplant, at this turning of the season. Golden blooms the goldenrod, and loud blows the nose. Brown curls the leaf of the tree along the sidewalk, because of all those merciless hot days. High is the electric bill, for the same reason. Torpid is the life style under the weight of the last days of summer.

What the public interest now requires, to get this country moving again, is some rain and an early frost.