The supply of American doctors is soaring, just when changes in the way health care is delivered and paid for are aimed at reducing the demand for their time. The number of doctors in the United States has doubled since 1960, from about 240,000 to nearly 500,000, and it will continue to grow well into the 21st century.

"I really see a crunch coming," says Dr. David Kindig, vice chancellor of the University of Wisconsin Center for Health Sciences, who moderated a panel discussion on the supply of doctors last week at the annual meeting of the American Public Health Association here.

The number of doctors is growing much faster than the rest of the population. In 1960, there were 148 doctors for every 100,000 Americans. By 1983, there were 210. By the year 2000, the figure is projected to reach 260.

By the year 2000 there will be about 700,000 American physicians -- including 145,000 women -- predicts Howard Stambler, director of the office of data analysis and management in the Department of Health and Human Services.

"The physician population is in a baby boom," says Donald Light, professor of health care science at the University of Medicine and Dentistry of New Jersey. "Some of the specialties are beginning to realize they're training their own competition."

Fears in the 1960s and 1970s of an impending doctor shortage have given way in the 1980s to worries about an impending doctor glut.

Even though medical school admissions declined slightly this year for the fourth year in a row, the supply of doctors will continue to grow because of the rapid expansion of the medical schools during the 1970s. Medical students who graduated during the past decade will continue to practice for the next generation.

"Whatever model you use, the conclusion is inescapable," says Dr. Alvin Tarlov, who chaired the committee that in 1980 produced a landmark study of graduate medical education needs. "There will be a steady decline in the demand for the time of individual physicians."

Although the sheer numbers are troubling, they don't pose an immediate crisis, says Tarlov, who is now president of the Henry Kaiser Foundation in Menlo Park, Calif.

"The system is quite flexible," he says. "It can accommodate these numbers. I think physicians will work for lower salaries and see fewer patients."

A small surplus of physicians has the potential to improve health care, Light agrees, by increasing accessibility, encouraging doctors to be more attentive to patients' needs and fostering prepaid health maintenance organizations (HMOs). But he says a large surplus would raise costs and increase frustration and generational conflict among physicians.

"I think we'll also see entrepreneurial hustling on a scale none of us would like to see, catering to consumers' fears, fantasies and gullibility," says Light.

Unless the economic incentives in medicine change, he warns, the projected doctor glut will merely raise total health costs without greatly improving care. That's because doctors -- not patients -- are responsible for ordering most of the medical care delivered in this country. The more doctors, the more demand for medical care and the higher the nation's total health care bill.

Every new doctor joining the health care system adds about $70 million in medical charges to the nation's health bill before retiring, Light says.

Does the impending doctor surplus mean that physicians' incomes will decline, or will they find new ways to boost demand for their services? Will doctors have more time to spend with patients? Or will they work shorter hours and take more leisure time?

No one knows for sure.

Already, fewer undergraduates are enrolling in pre-med programs, perhaps because they are concerned that a medical practice no longer guarantees a comfortable living. The number of applicants to medical school fell 8.5 percent last year -- the first significant drop since 1978, according to the Association of American Medical Colleges.

Another key factor is the projected continuing growth of HMOs -- whose membership has leaped from 1.4 percent of the population to 7.7 percent in the past 15 years. Dr. Paul Ellwood, a health care consultant who coined the term health maintenance organization, has predicted that HMOs will have 150 million members by the year 2000.

Tarlov uses a more conservative estimate of 120 million HMO members by the end of the century. But he agrees that growth of HMOs could have a substantial impact on the need for physicians, because prepaid plans such as HMOs use far fewer doctors than the traditional fee-for-service health plans.

HMOs generally use about 110 physicians per 100,000 members. If that ratio continues, they would employ about 132,000 doctors in the year 2000. That would leave more than half a million doctors for the 150 million Americans not enrolled in HMOs -- a ratio of 331 doctors per 100,000, or three times the ratio in HMOs.

In some specialties, the gap between HMOs and fee-for-service would be even larger. Proportionally, there would be 12 times as many cardiologists, for example, in the fee-for-service sector as in the HMO sector, Tarlov estimates.

Other health care specialists besides MDs are in a boom cycle. The ranks of chiropractors, registered nurses, licensed practical nurses and nurse-midwives all are expected to triple by the year 2000, compared with 1960. The number of nurse practitioners is expected nearly to triple in the same period.

A basic paradox continues to confound American health policy: The nation has both a surplus and a shortage of doctors. In many rural and inner-city areas, there are too few doctors, while many affluent metropolitan areas have an oversupply.

Convinced of an impending shortage of doctors, Congress boosted appropriations for construction of medical schools in the 1960s. In 1971, Congress further increased aid to medical schools and encouraged them to expand their enrollments. The number of medical schools has risen from 94 to 141 since 1960.

"Yesterday's solution is today's problem," says Dr. Brian Biles, a former congressional aide who is now deputy director of the Maryland state Department of Health and Mental Hygiene.

By the mid-1970s it became clear that merely increasing the total number of doctors would not solve local shortages. Incentive programs to encourage young doctors to move into medically underserved areas were established, but they were never well funded and have been further cut since 1980.

"If they were inadequate in the 1970s, they verge on nonexistent today," says Biles.

The huge increase in the number of doctors nationally won't have much effect on doctor shortages in remote or inner-city areas, Biles says, because most of the projected growth is in areas where there are already a lot of physicians. The supply of doctors in California, Pennsylvania and the District, for example, will continue to grow rapidly, while doctor-poor South Carolina will not share in the growth.

"The American political system," Biles says, "doesn't deal very well with projected crises."