NOW COMES the serious side of the year. Labor Day is here and, regardless of the calendar and the weather, summer is over. No more lying on beaches, no more paddling around lakes, no more afternoons in the park. The pace picks up. Another year begins.

It's school year that sets the rhythm of life in most households. It begins in a few days with the season of high hopes, which, as the weather gets colder, turns into the season of hoping for the best. There's a short period of frantic activity just before Christmas, succeeded by the long march through winter and onward until everyone collapses, exhausted, in late spring. Most Americans have now spent so much time in various schools that, even when they happen not to be enrolled, they still feel the turn of the seasons -- like old farmers who've moved into town. At Labor Day, there's alwasy the impulse to rush out and buy a clean new notebook, that powerful symbol of fresh beginnings.

Because of the falling birthrates, there will be fewer children in school this year than there were a decade ago. But there will be many more adults in the universities. Americans used to live simple lives in which first they went to school and then they went to work. Now their work keeps sending them back to school. For many, the process of getting ahead is now measured in credit hours. Which courses do you need for the next level of certification, and the next rung up the ladder?

A higher proportion of Americans, incidentally, is now employed than ever before. Out of every 100 Americans over 16 (and not in jail), 65 have jobs. Among men, the proportion who are working or looking for work has been falling slowly over the years as educations lengthen at one end of the age scale and pensions improve at the other. That was predictable. But the great number of women pouring into the labor force is another matter. Fully half of all women now hold jobs, compared with only a third a generation ago. In recent years, adolescents of both sexes have been finding jobs in higher proportions than ever.

There are two competing explanations for this steady rise in the proportion of the American population that is employed. One is inflation. As families struggle with rising prices, more wives and more children feel compelled to help by going to work. But there's more to it than economic compulsion. Even in the most affectionate of families, having an income of one's own demonstrates an important kind of independence.

On Labor Day, it's worth a moment to consider the worth of a job to the person who has one -- and to the person who wants one. It goes beyond the value of the wages earned. At the beginning of each summer, this country celebrates its national Independence Day. Now, at the end of summer, it celebrates the idea of labor and what you might call a personal independence day. Tomorrow, of course, the celebrations of summer are over and the country gets down to work for another year.