THE RESULTS of the Defense Department's vocational aptitude tests are hardly surprising. They reflect the familiar racial and ethnic disparities. The average scores for young people who are white were significantly higher than for those who are Hispanic, and the average for the Hispanics was higher than for those who are black. A representative group of nearly 12,000 people between the ages of 18 and 23 took this series of aptitude tests in 1980. The Pentagon's purpose was to see whether the recruits coming into the armed services, in the absence of a draft, were representative in certain abilities of the whole population.

Disparities of scores on this scale, among large sectors of the population, are unhealthy and a reproach to a country that asserts equality of opportunity. The validity of these tests is, unfortunately, beyond dispute. As the Pentagon emphasizes, they do not measure intelligence or potential. But they accurately predict the probability that a person will succeed in a wide range of kinds of vocational training. Since differences of this magnitude are not consistent with American principles, what is to be done about them?

These test results also contain other disparities that illuminate the racial and ethnic ones. When the scores are broken down by region, New England is the leader. At the bottom of the list comes the South--including, incidentally, the Washington region. The results also show a correlation--a dramatically strong correlation--between these young people's test scores and the number of years of education that their mothers received. That relationship is an emphatic warning that the educational failures of one generation will continue to exact a toll in the next. In reflecting on the racial and ethnic differences in performance on this kind of test, it is important to remember that they are not unrelated to the regional differences. The low score of a young man trying to join the Army today in Michigan may well be connected, in some part, to the quality of education that a girl living in rural Alabama received in the 1940s.

To say that these effects are deep-seated is hardly to say that they cannot be remedied. Otherwise, since neither Adam nor Eve graduated from high school, the scores would be a great deal lower than they are. But if you are at all interested in the abilities of young people going into the military services in, say, the year 2020, and whether the present racial disparities will still appear then, you had better pay attention to the schooling of their parents, who are now in the second grade. These test scores sound a note of caution regarding Mr. Reagan's new federalism, with its emphasis on returning social policy to the states, for they draw attention to the strong national interest in ending severe differences in basic social services--education, health, nutrition--from one state to another.

At a time when the country is increasing its defense spending and holding down just about everything else, these scores provide compelling notice that there is more to military strength than buying tanks. The distinction between a strong defense and the social programs is not quite so clear as you might think from listening to the current budget debate. In these test scores, the Pentagon draws that crucial connection.