AMERICA HAS had trouble in the 1980s with some aspects of world leadership, from industrial competitiveness to arms control, from the Pacific Rim to the Persian Gulf. But in one area -- higher education -- America today reigns supreme. And that has created a problem of its own: a tidal wave of foreign students.

American brain-power has always been enhanced by immigrants. What's new is the extent of foreign penetration of American higher education. As of 1986, more than 300,000 foreign students were enrolled in American universities, 60 percent of them in technical fields. In contrast, only 30,000 American students attend universities overseas. Of these, perhaps 3 percent study in areas such as engineering, computer-science and physics.

Foreigners who win PhDs from American universities provide the most impressive (and to some U.S. taxpayers, shocking) evidence of the foreign-student boom. Over the past two decades, the National Science Foundation has monitored trends in engineering. The statistics show that from 1963 to 1983, the percentage of foreign-born doctoral students in industrial engineering grew from 7 percent to 68 percent; in mechanical engineering from 28 percent to 60 percent; in electrical engineering from 23 percent to 55 percent; in chemical engineering from 22 percent to 52 percent; incivil engineering from 37 percent to 63 percent.

The other most attractive field, embracing aspects of both science and engineering, is computer science (including artificial intelligence, robotics, software engineering, cognitive science). As of last year, foreign students made up 40 percent of PhD candidates in such fields as:cognitive science, at the crossroad of artificial intelligence and psychology, which examines the mechanisms of the brain; medical information science, leading to computerized expert systems in medicine; software engineering; and non-linear mathematics, which studies the behavior of turbulent and chaotic systems.

For the first time in modern history, one country seems to serve, in the advanced sciences, as the university of the world. "The United States is viewed, world wide, as the place to come and study in the sciences," says John Reichard, vice president of the National Association for Foreign Students.

The intellectual migration has provoked an intense debate: Is it good for America to be educating the world's best and brightest? Is it good for other countries to lose some of their best brains every year? What kind of policy is it that subsidizes America's corporate rivals with millions of dollars worth of vital research?

There's little doubt that American taxpayers are subsidizing the foreign-student boom. The tuition paid by foreign students is "less than half" of the yearly cost of training a graduate engineering student, according to the University of Michigan at Ann Arbor. This strikes a growing number of Americans as unfair. Why, they ask, should an American university charge a grad student from Tokyo the same as the kid from Toledo? If the Japanese student wants our education so badly, let him (or his government) pay for it.

Clearly, foreign governments aren't paying a significant share. An NSF inquiry covering over 100 leading research universities reveals that total foreign contributions accounted for less than 2 percent of their research budgets.

But that may not be the principal problem. "We don't have too many foreign students, we have too few Americans. We are not attracting enough of our students into graduate schools," declares the director of the American Society for Engineering Education, Karl Willenbrock. Moreover, according to the NSF, 57 percent of the 5,000 foreign students granted doctoral degrees in the sciences from American universities last year said they intended to remain in this country.

"We have done very well with the people we got from other countries. They include Albert Einstein and Enrico Fermi," concludes Peter Renz, administrator of the Conference Board.

The question remains: Has the great American university system really turned, unconsciously, into a foreign Fifth Column undermining America's economic leadership and standard of living? We do not pretend to pronounce a verdict. But some facts can help us prepare a balanced policy:

Foreign students give the U.S. as much as they get. They are paying for their long years of study with the most precious and expensive commodity, the one the US most needs today: more knowledge, new knowledge, provided by their labor. By working in American laboratories for 3 to 7 years of post-graduate study, thousands of young experts are by themselves the most efficient "subsidy" to scientific progress and economic development. And a large majority of them do not choose, at graduation, the well-paid jobs offered by industry, but remain in the tough, competitive life of research and teaching.

Foreign students are needed to meet American research and development goals. If most of the foreign students were to return to their countries, it would be an American disaster. The fact that more than half of them choose to stay (a number that would increase if the US immigration rules were less restrictive), multiplies the productivity and creativity of American science and engineering.

The fact that a substantial number choose to return home is also very good. The great American knowledge-machine could not function for very long if it kept siphoning away the brain-power of America's partners around the world. The loss foreign countries experience when students come here is more than repaid by the new knowledge and skills they acquire when nearly half of them return.

We believe that a 50-50 trade is a fair ratio. It has become important to America that a substantial fraction of the trained foreign students remain at work here as long as there is a large deficit of U.S. applicants to the long, strenuous, underpaid, doctoral programs. The next 10 to 15 years are crucial. During that period, the number of competing international laboratories, corporations, learning-systems, will continue to increase. These years, between now and the end of the century, will decide whether America remains in the first rank, or falls behnind. The critical difference might well be made by the capacity to retain a good half of the best and brightest "foreign" students.

American universities need more American graduate students. The simple fact is that too few Americans apply to graduate programs. The vast majority accept a job after earning their bachelor's degree, or enroll in law or business colleges, opting for. professions offering larger financial rewards than research does. They won't change this view because Congress passes new laws, but because they are stimulated to compete with their colleagues from abroad.

We already see it today in the classroom. The pride of American students is on the line. They do not easily accept being surpassed by those who work with extra energy because they are immigrants. These "invaders" inscientific fields are often among the top 10 percent of graduate students and even at the very top. But a striking sign of America's natural generosity and courage in competition is that the excellence of foreigners breeds almost none of the anti-foreign sentiments observed in many other parts of the world.

The historian Barbara Tuchman recently expressed her misgivings about the future: "In the United States one feels a deteriorating ethic in most spheres . . . . When people do not care and have no goal in view they do not function at their utmost. They grow lax and accept defeat. Incompetence is the companion of decline. Competence is the ability to do work expertly, neatly and correctly. To raise the level of public understanding from frivolity to a readiness to take things seriously will require a great and concentrated national effort -- if we can figure how it may be done!"

In meeting this new challenge, everything will depend on maintaining this country's excellence in higher education and repairing the quality of primary and secondary education. If foreign students should ever stop pressing for admission to U.S. universities, it would be a sign that America has lost its last great resource.

Jean-Jacques Servan-Schreiber is chairman of the International Committee at Carnegie Mellon University and a former French cabinet member. Herbert Simon is a professor of computer science and psychology at Carnegie Mellon University.