COMMUNITY COLLEGES'enrollment has risen over the past decade, but the number of their students actually earning degrees each year has been falling since 1983, according to the American Council on Education. These two-year schools, with their open enrollment and low tuitions, are the bridge to a four-year education for many students with not much money and perhaps weak high school preparation. It is a matter of some social urgency to understand why the number of people crossing the bridge is declining.

The more optimistic explanation is simply that more students are enrolling in community colleges part-time -- a change that's been amply documented as more people decide to study without leaving their jobs. Perhaps they are only getting their degrees more slowly. More troubling is the possibility that more students are coming in without the initial ambition to transfer, or that the increasing eagerness of the community colleges to defray costs by turning to job training is leaching those students away from degree-oriented academic classes.

The vocational, non-degree side of community colleges, always important, is undoubtedly getting more so. You have heard much talk about the enormous changes overtaking American industry and the need to retrain labor to deal with increasingly higher levels of technology. The community colleges are doing an important part of that retraining, and they are making themselves a crucial part of the process through which this country will adapt to the demands of an increasingly competitive world economy.

But the vocational side of the community colleges' mission can't be allowed to overshadow their academic responsibilities. Obviously many community college students want only vocational training and enroll specifically for that reason. But if it is essential to provide production workers with the opportunity to turn themselves into skilled technicians, it's no less essential to provide technicians with the further opportunity to turn themselves into fully qualified engineers and administrators.

No single statistic can tell you as much about the future of the American economy as the number of college degrees awarded annually. The community colleges are the indispensable means of keeping access to higher education open to everybody. The diminishing number of degrees awarded there is a flashing yellow light indicating that the trend is running the wrong way.