THE CONCERN over the quality of American schools keeps coming back to one central point --the shortage of talented and well-trained teachers. Perhaps the trouble started with the birthrates two decades ago. As the numbers of children dropped, school boards began to feel that they were in a buyers' market for staff. Many of the better teachers left. With fewer jobs available, fewer college students considered teaching--and among those who did, the level of ability fell. But the birthrates stopped falling seven years ago, just about the time that the present first-graders were born.

Now the people who care about education--and in this country it's a large majority--have begun to realize that the schools are losing their capacity to teach some of the crucial subjects. It's most visible in math and science, but not limited to them. Better salaries for teachers are going to be necessary, but that alone can't do it. There are interesting possibilities in the movement toward closer cooperation between schools and universities.

Beyond complaining about poor preparation of the incoming freshmen, most of the universities have contributed little to the schools in recent years. On the contrary, they have made matters worse with the relaxation of their own admissions standards and confusion over what they want. But things seem to be changing. Last month at Yale, the presidents of some 40 colleges and universities met with school officials from most of the states to see whether they couldn't do better.

One subject was the recruiting of future teachers. Ernest L. Boyer of the Carnegie Foundation suggested that if colleges could offer scholarships to attract athletes, perhaps they could use the same device to draw students into teaching. Another question was the development of incentives to keep the best teachers in the classroom, instead of pushing them into administration. But how does a school keep teachers from becoming isolated in the classroom and going stale?

How about joint appointments between schools and neighboring colleges? It's an idea that might well be usefully pursued here in the Washington area, with its wealth of strong university faculties. There are many gifted teachers in American schools, as grateful parents know. But there are not enough of them, particularly in those fields where the schools must compete with private employers. And the flow of adequately equipped new arrivals is down to a trickle. Improvement of the schools is going to require more support and surer rewards for the people who will teach there.