Next Monday marks the 94th anniversary of an important day, a day set aside to honor a major source of America's greatness - its working men and women.

Since Labor Day came about primarily at the instigation of unions, this holiday is also an appropriate occasion to assess the condition of organized labor.In many ways, unions are ailing. Their membership constitutes less than 18 percent of the non-agricultural labor force, down from a peak of 34 percent in 1955. As the relative importance of the auto, steel, rubber, and mining industries has waned, so have the vigor and clout of unions.

But it would be a mistake to conclude that organized labor is on a treadmill to oblivion. Despite the decline of membership elsewhere, unions remain strong in government - particularly at the federal level.

Moreover, Congress lately has been addressing more and more programs dear to organized labor. Among such matters are trade policy, plant shutdowns, the minimum wage, and catastrophic health insurance.

The fact remains, however, that the American economy is changing in ways that don't necessarily favor organized labor. As old manufacturing industries provide fewer and fewer jobs, the slack is increasingly being taken up by the rapid growth of the service sector where labor unions have historically held little appeal to workers.

Even more change seems to loom ahead as technology seems bound to play an increasing role in the creation of new jobs. Such changes pose challenges not just for unions, but also for individual workers.

As the U.S. Department of Labor notes, "Workers must be prepared for rapid changes in jobs caused by technological advances or economic forces such as foreign competition. It will not be unusual in the future for workers to switch jobs or careers four or five times in their lives."

This situation poses a big challenge for the schools. It puts them under increasing pressure to come to grips with the adult illiteracy that now afflicts some 23 million Americans. It means schools must do more to curb drop-outs, which in some high schools reach a level as high as 50 percent. And it points to the need for more emphasis on the basic skills of reading, writing, and arithmetic.

As for individual workers, a rapidly changing economy means they must become more flexible - which is another way of saying they need to keep improving their skills and learning new ones long after they have left school.

But then American labor, individually and collectively, is accustomed to challenges, having surmounted plenty of others ranging from inflation and recession to depressions.

As workers mark another milestone this Labor Day, the future is demanding - but there's ample reason for optimism.