Washington's medical mandarins are wringing their hands over what they see as a bank-breaking doctor surplus coming from record enrollments in the nation's medical schools.

But what might as well be acknowledged about the doctor explosion is that medical education is culturally and politically invulnerable to throttling back. And once that point has been absorbed, some thought should be given to oportunities that might be found in the lamented "surplus" for turning loose some supply-and-demand froces on the economics of health care.

Recent experience doesn't offer encouragement for that possibility, since medicine is the only remaining line of work in which superior earnings await every certified job seeker. As high as they are, however, doctor fees are only about 20 percent of the nation's $200-billion-a-year medical bill; the big costs are in the medical services and supplies that they order for their patients, such as hospitalization, tests, drugs and medical devices. Thus, large and annually increasing sums are associated with each medical practitioner -- which is why the paymasters for government health-care systems look with horror on the basic statistics: in 1975, the number of doctors in practice totaled 378,000; the figure is now 450,000, and by 1990, the total will be around 600,000, according to a report published last week by the congressional Office of Technology Assessment. In terms of doctor-population ratios, the United States was at 176 per 100,000 in 1975; the 1990 figure is forecast at 235 per 100,000, and that's reasonably reliable, given the predictability of enrollments and populations trends. Measured by the ratios of industrialized countries with admirable health records, the United States has plenty of doctors, though too many are clustered in some places, while insufficient numbers are in others.

Meanwhile, the great medical-education machine continues to produce them, at the rate of some 16,000 per year, with the output due to rise soon as several new schools join the 126 now in operation. The question of why we continue to turn out so many new physicians when it would be sensible to make more effective use of existing ones has occupied many scholarly conclaves. But there's no real mystery in America's extraordinary overspending on medical training. Medicine is a high-prestige, high-income profession without peer in terms of combining doing well and doing good.

Even with post-college training taking a total of six to eight years and some tuitions running at $15,000 a year, every school receives more qualified applications than can be acepted. The yen for joining the profession is so strong that some 5,000 Americans who couldn't gain admission at home are studying abroad -- usually at premium tuitions -- in the hope of completing a long and roundabout route to practice in the United States. Customer demand for medical training has, in fact, created a bizarre political paradox in medical education: keeping existing schools above water financially while fending off promoters who want to start new ones.

The coming doctor glut is regarded with foreboding because medicine in its recent history has managed to detach itself from ordinary economics. The process all along has been that doctors prescribe, patients receive and insurance organizations pay. The system has been durable and highly resistant, if not altogether immune, to promoting thrift in the provision of health care. But this need not necessarily remain the case in the coming era of abundant medical manpower, and there are signs that suggest that shifts along those lines may be in the works.

In many communities, particularly in the fast-growing Sun Belt -- popular areas for newly trained physicians -- open advertising keyed to price and accessibility is fast becoming a part of medical practice. Among the rapidly growing facets of medical practice are the privately operated medical offices, known in the trade as minor emergency clinics, that are springing up in heavily trafficked areas, such as shopping centers. They are well equipped, staffed for long hours and strategically priced just below the going rate for a visit to a conventional office.

Note these developments, small as they may be at this point, and then consider that the big insurance systems, Medicare, Medicaid and the "Blues," are at long last encountering serious resistance from those who, in one way or another, provide the wherewithal for their reimbursements to the health-care system. The response of the insurers is to demand medical economizing, not because they want it, but because there's no other out.

What ought to be recognized about the doctor surplus is that it is unstoppable; the task of policy-makers, then, is to exploit it for bringing care to those who have been bypassed by our medical affluence and for bringing restraint to health economics.