A MILLION HIGH SCHOOL seniors take the College Board's Scholastic Aptitude Test every year. Those test scores have become a broad and sensitive indicator of the academic abilities and interests of the youngsters who are, generally speaking, the best equipped one-third of each year's graduates. Fifteen years ago, the SAT scores began to drop. It is beyond dispute that one reason for the decline has been the erosion of standards - or, perhaps more accurately, the confusion over standards - that has beset the schools. Throughout the country, schools are now struggling to reverse this trend. That is why the SAT scores are beginning to get the same kind of intense attention as some of the economic statistics, like the unemployment rates. They are numbers that tell us, in a rough but useful way, how we as a society are doing in an endeavor to which the American tradition assigns fundamental importance.

Last year the average score for the verbal half of the SAT stopped falling. That's a hopeful sign.But the hope is diluted by the score for the mathematical half, which again fell a couple of points. So did the average scores for most of the achievement tests on specific subjects like history and literature.

American schools are on the road back from the great romantic excursions of the late 1960s and early 1970s. In those heady days it was what you felt that counted. Now, once again, it's what you know and what you can do. Grading no longer seems to be under attack as elitist and repressive; the honor rolls are coming back.But there's a lot of ground to be recovered. Even if the long declining trend in verbal SAT scores has ended, the average score is now 49 points lower (on a scale that runs from 200 to 800) than it was in 1963. As statistical analysis has demonstrated, the difference is not in the tests.

If high school students' attitude toward their education has become more serious over the past several years, it has also become more narrowly vocational. When these youngsters take the tests, the College Board asks them what they intend to study in college. Currently, the leading choices are business management and accounting. Premedical courses and nursing attract very large numbers, if not quite so many as in the past. But the programs that lead to law school are growing, and engineering is enjoying something of a resurgence. Education still attracts a great many students, despite the rather bleak prospects of employment in shrinking school systems. As for the humanities and mathematics, the number of students pointed toward them continues to decline.

The quality of schools depends, in the last analysis, on the quality of teachers, and here the College Board's computer offers a warning. Breaking down test scores by the students' prospective fields of interest, it showed that those going into teaching stood very near the bottom of the rankings. At present, the future teachers are being drawn largely from the students who have been least successful on this basic test of academic ability. It is a pattern that does not promise much help for the students who will be taking the test a generation from now.