Peter Bourne, once special assistant to President Carter on health issue, informs us that the "country can beneficially absorb an unlimited number of individuals trained as physicians" ["How Many Doctors Are Enough?," oped, April 3]. He would let the market determine how many is enough, as it does for lawyers or plumbers. Government should impose no limits. Could he possibly mean what he says?

If medical school were no more subsidized than law or business schools, tuition would be $15,000 to $20,000 a year. The average medical student receives more in public subsidies than he pays in tuition. Patients in teaching hospitals also contribute large subsidies for medical education. Either loan programs would have to be vastly expanded, or our medical schools would be filled mainly by the children of M.D.s.

If health care were sold like plumbing or legal services, there would be no public subsidy for customers: no Medicare, no Medicaid, no insurance coverage. Many would not be able to afford medical care, just as many cannot afford lawyers, mechanics or plumbers. Some M.D.s would be collecting unemployment compensation right now. Inflation in medical costs might be a thing of the past. After all, the patient now pays only 30 percent of medical costs and 10 percent of hospital costs. If physicians and medical schools fatten at the public trough, they'd better be prepared to whistle "Hail to the Chief."

Bourne says that we have no valid criteria for determining how many M.D.s are enough. In fact, there are a number of informed estimates, including one by the Public Health Sevice. The current ratio of doctors to population already exceeds all estimates of need of which I know. Both Secretary of Health, Education and Welfare Joseph Califano and the National Academy of Sciences have warned us of the impending surplus and resulting medical cost inflation.

Bourne claims that more doctors help control inflation in medical costs. If so, costs would be lower in New York than in Arkansas or Mississippi, since New York has more than twice as many M.D.s per capita. The reverse is true. The more doctors, the higher the prices.

Finally, Bourne believes that flooding the market with doctors will eliminate shortages in rural areas and other unattractive settings, or surplus M.D.s will find employment in health-policy jobs. Training surplus doctors at huge public expense so that perhaps one in 10 may end up where needed, and the others in jobs for which they have not been trained, is not an intelligent policy. The number of M.D.s has increased by two-thirds in the past 20 years without reducing the shortage in rural areas at all. In fact, some rural areas will never have a doctor; hardly any will ever have a full complement of specialists and hospital facilities. For the same reasons, they will never have opera houses and daily newspapers. Since the rural population is as healthy as city folk, it is not at all clear that they need more M.D.s. Nor is it clear that more doctors than we already have is good for our health.