The American Medical Association voted yesterday to form a labor union to bargain on behalf of doctors for better pay and working conditions -- a dramatic attempt to give physicians more clout in an era of managed health care.

The decision to organize doctors into bargaining units represents a radical departure for one of the oldest and most conservative professional organizations in the country. It signals the profound discontent of many of the 700,000 physicians in the United States over the direction of the nation's health care system.

The AMA's move also appears certain to inflame an already-smoldering debate over whether patients stand to gain or lose if their doctors can seize more leverage against health maintenance organizations and other insurers. Such plans have acquired vast powers in the last decade to dictate most Americans' care.

In setting up what they are calling a "national negotiating organization," AMA officials contended that only through collective bargaining can doctors win back control over which drugs they may prescribe for patients and how much treatment they can provide.

But the AMA vote came just a day after the chairman of the Federal Trade Commission cautioned members of Congress that giving doctors greater freedom to unionize "would be bad medicine for consumers."

Testifying before the House Judiciary Committee, FTC Chairman Robert Pitofsky warned that pending legislation to exempt health professionals from antitrust provisions would allow doctors to band together to demand higher fees from health plans, ultimately forcing patients and their employers to pay higher medical costs.

With its decision yesterday, the AMA would essentially be joining groups like the AFL-CIO in an effort to woo the small but rapidly growing cadre of doctors who have already shown an interest in joining labor unions.

Randolph C. Smoake Jr., chairman of the AMA's board, said the association's new labor organization will help groups of doctors across the country establish themselves as bargaining units to negotiate contracts with hospitals and health plans. He said the AMA will not dispatch organizers to drum up union support but will instead respond to requests for help from local medical communities.

Under current law, only physicians with a direct employer -- such as a hospital, health plan or government health department -- are allowed to unionize, and these are the doctors that the AMA will target at first. About one in seven doctors are part of such plans.

However, the pool of physicians would expand exponentially under the bill before the Judiciary Committee, which has strong AMA backing, that would permit unionization by doctors who work by themselves or in small group practices. But in several parts of the country, doctors and health plans have been sparring lately over when exactly a physician is an employee.

Doctors' efforts to define themselves as employees reflect a remarkable shift. Since its founding a century and a half ago, the AMA has devoted much of its time to fighting to preserve physicians' autonomy.

Against that backdrop, Paul Starr, a Princeton University historian who is an authority on the history of American medicine, yesterday called the AMA's decision "a watershed" that "reflects a momentous change in the economic position of the medical position from the time when nearly all doctors were independent businessmen . . . to a time when large numbers are either on salary or face very large buyers of their services."

Starr also interpreted the AMA's action as an attempt to create a counterforce to the recent consolidation of health plans across the country. "Each [side] is trying to represent a larger power in order to have more bargaining leverage," he said.

Yesterday's decision at the association's annual meeting in Chicago was divisive. The AMA did not release a tally of the vote, but the debate among its delegates beforehand was impassioned.

In an interview afterward, Collette Willins, a 35-year-old family physician who works in a four-doctor group in Cleveland, said she welcomed collective bargaining. "The problem is, little old me . . . going up against an insurance company," she said. "I have no negotiating power . . . [to] stand up and fight on behalf of my patients."

On the other hand, Lanny Copeland, who works in Albany, Ga., and is president of the American Academy of Family Physicians, said, "I think I'll be embarrassed when my first patient asks me if I'm a member of the union." Noting that the typical U.S. doctor's income is just below $200,000, he said, "The average connotation is, the biggest thing unions do is hold out for more money. . . . It smacks a little bit of greediness."

Even as they embraced collective bargaining, the AMA's top officials sought to distance themselves from other unions, saying that they would never go on strike, for example. "Traditional unions are there primarily to care for their employees' needs," AMA President Nancy W. Dickey said. "We are looking for a vehicle that will allow us to carry out the covenant we have with our patients."

CAPTION: FTC Chairman Robert Pitofsky has warned against exempting health professionals from antitrust laws.