Faced with what they see as a steady erosion of professional autonomy and control over the practice of medicine, doctors are beginning to unionize.

The numbers are small -- fewer than 25,000 of the nation's 502,000 doctors -- and most physicians still regard a doctors' union as a contradiction in terms. But it is a measure of the drastic change taking place in the delivery of health care that unionization is being considered at all in a profession where the average annual net income exceeds $100,000.

Massachusetts last week became the eighth state in the nation -- and the first in the East -- to establish a doctors' union, joining Arizona, California, Colorado, Hawaii, Michigan, Oregon and Utah. Similar organizing efforts are underway in other states, including Connecticut, Florida, Illinois, Indiana, New York, Pennsylvania and Washington, union leaders say.

"We formed the union to try to slow the downward slide in both the professional and financial fortunes of physicians," says Dr. Sanford Marcus, president of the California-based Union of American Physicians and Dentists (UAPD), formed in 1972.

"It's a whole new ballgame for doctors," says Marcus. "We've been lone professionals. We've not been a group noted for our ability to band together."

Medical interns and residents at many hospitals also have organized unions affiliated with The National Federation of House Staff Organizations. One such union went on strike two weeks ago at Interfaith Medical Center in Brooklyn.

Organizers say several new factors in the medical climate -- including for-profit medicine, intensifying efforts to reduce hospital use, and a glut of doctors in some areas -- make unionization feasible now in a profession that traditionally regarded unions as anathema.

"Far and away the most important," says Dr. John T. LaRossa, president of the newly organized Physicians and Surgeons Association of Massachusetts, "is the absolute loss of control we are beginning to experience in treating our patients."

To reduce medical costs, third-party payers -- such as insurance companies and the government -- increasingly are trying to limit unnecessary use of hospitals by a process called "utilization review." For example, under some insurance plans, a doctor cannot admit a patient to the hospital for elective surgery without getting the approval of a review panel of doctors and nurses. If the hospitalization is deemed unnecessary, coverage is denied.

LaRossa cited the case of one of his patients, an elderly woman with diabetes who needed surgery to remove cataracts from both eyes. His decision to admit her to the hospital was stymied by an insurance company review panel ruling that cataract surgery should be performed in an outpatient setting, without overnight hospitalization.

"There was a blanket refusal to admit her to the hospital," LaRossa says. "It took us seven weeks of calling the insurance company to finally get them to allow us to admit her to the hospital for this surgery and stay there long enough to get her vision back to the point where she could safely go home."

Others worry that the government's new payment system for Medicare -- under which hospitals are reimbursed a set amount for each case, according to the diagnosis, regardless of how long the patient is hospitalized -- encourages hospitals to discharge patients "sicker and quicker."

"Things have gone too far in justifying cost containment," says LaRossa, an endocrinologist in private practice in Wellesley Hills, Mass. "Cost control to an insurance company means restricting services. We're not opposed to cost control, but cost control must be viewed in the context of the whole patient."

Doctors are "the only ones who think of patients as individuals," he says, "not as dollar signs."

But a spokesman for the Blue Cross and Blue Shield Associations says utilization controls are intended not to make medical decisions for the doctor but to make the doctor justify those decisions.

"It really isn't that the insurance company is usurping control from doctors," says Dr. William Y. Rial, executive director for representation and information. "It's that the physicians are used to having no one question their judgment."

Insurers are simply responding to demands from government and business to cut medical costs, says Rial, a past president of the American Medical Association. That can be done without lowering the quality of care, he says, by reducing unnecessary surgery and hospitalization.

"You want to know who really needs to be in the hospital?" Rial says. "Look who's there on Christmas day."

Another factor encouraging unionization among doctors is the growth of for-profit chains of hospitals and other health care facilities.

"We are being conglomeratized," Marcus says. The commercialization of health care, he says, removes from doctors professional control over health care "by making a cost accountant more important than a doctor in determining what is best for the patient." TT he growing number of doctors also was a factor in the establishment of T physicians' unions in California and Oregon, says UAPD president Marcus. One of every 163 residents of Oregon, and one of every 183 residents of San Francisco, has an M.D. degree, he says -- about triple the national average.

The oversupply of doctors has held down salaries at for-profit hospitals, health maintenance organizations (HMOs) and other facilities that hire physicians as direct employes.

Doctors are like the United Airlines pilots, says Marcus -- respected, highly skilled professionals who take the public's lives in their hands and are "in the process of being mass produced and having their bargaining power taken away."

Ironically, many of the concerns of unionizing doctors about loss of autonomy sound remarkably similar to those voiced by the AMA. But union organizers say the AMA cannot serve the purpose of a union because such representation would be considered an illegal restraint of trade.

"They articulate all the grievances," Marcus says of the AMA, "but there's not a damned thing they can do about it except wring their hands."

The new Massachusetts union will represent doctors in two basic ways, a spokesman says. It will bargain collectively on behalf of the growing number of doctors who are salaried employes of hospitals, HMOs and surgery centers, and it will represent private physicians as they negotiate individually with third-party payers such as Medicare, Medicaid or insurance companies.

Dues for the Massachusetts union are $400 a year. The organizing committee of 50 members sent out a solicitation letter to every doctor in the state last week -- some 16,000 in all. LaRossa says it's too early to tell what response the letter will draw.

Union leaders take pains to avoid raising the threat of a possible doctors' strike.

"That's the farthest thing from our minds," says LaRossa. "We can't be patient advocates by withholding care. We would never withhold services from patients."

Unionization of doctors -- virtually unheard of a decade ago -- is a symptom of radical change in American medicine, union organizers say. More and more members of one of America's most autonomous professions, extraordinarily successful at opposing public regulation, now fear a loss of independence and control.

In the 1970s, writes sociologist Paul Starr in his Pulitzer Prize-winning book, "The Social Transformation of American Medicine," doctors and hospitals mistakenly saw liberal government as their enemy, when the real threat lay in the demands they were placing on private health insurance, which could not bear the cost.

"The great irony," Starr writes, "is that the opposition of the doctors and hospitals to public control of public programs set in motion entrepreneurial forces that may end up depriving both private doctors and local voluntary hospitals of their traditional autonomy."