The National Labor Relations Board has ruled that interns and resident doctors in the nation's private teaching hospitals are eligible to form unions--and also strike--to negotiate better wages and hours as well as better working conditions.

In a Nov. 26 ruling released yesterday, the board decided 3 to 2 that interns, residents and medical fellows are employees, overturning a decision 23 years ago that classified the workhorses of the medical field as students. Many typically work 80 or more hours a week as they undergo training to become full-fledged doctors.

The ruling, in a case involving Boston Medical Center, is the latest in a series of victories for labor unions in the medical industry, but it is unclear how it will affect medical practices or prices. Neither the Association of American Medical Colleges nor the American Hospital Association had a formal statement on the NLRB ruling yesterday. Both groups said they probably would comment today.

The American Medical Association this year approved unionization for certain salaried doctors, and several major unions have begun signing up doctors in addition to lower-paid health-care workers.

The ruling was immediately hailed as a major victory for both doctors and labor by the Committee of Interns and Residents, which brought the case before the NLRB early in 1997. The CIR is an affiliate of the 1.3 million-member Service Employees International Union, which has been aggressively signing up health-care workers, including doctors, in recent years.

"This decision shouldn't be taken in isolation," said Mark Levy, CIR executive director. He said his organization will now seek to unionize the approximately 90,000 eligible residents, interns and medical fellows.

The CIR represents 10,000 interns and residents at 60 public hospitals in New York, Massachusetts, New Jersey, Florida, California and the District.

"We're quite disappointed," said Joseph Keye, general counsel for the Association of American Medical Colleges. "We think they [the NLRB] made the wrong decision. It's both bad for education and labor relations."

Keyes said, "The chief characteristic of the National Labor Relations Act is the right to strike, compared with state institutions, which allow doctors to organize but they can't strike." He said his organization would be working with its members "to try to help them understand the rules of the game" so interns and residents won't feel compelled to strike.

Boston Medical Center is a peculiar case in that it had previously recognized the CIR as the union representative of its interns and residents. But when the medical center was sold to a private firm in 1996, the new owners moved to decertify the union on grounds that the 1976 NLRB ruling prohibited union representation.

It was that move to decertify the union that brought the case back to the NLRB.

In its order yesterday, the board ordered an election to be held within 30 days. Levy and Ladi Haroona, CIR president, both expressed confidence the union would easily win the new election.

The NLRB decision cannot be appealed, according to officials on both sides of the case.

"Marcus Welby retired a long time ago," Levy said. "His grandchildren are the new doctors, and medicine just isn't the same." With the growth of health maintenance organizations and managed care, Levy said, "80 percent of those young doctors who finish their specialty training go on to work in salaried jobs."

He said for many doctors already in practice, "house [hospital] staff are sort of like the miner's canary, and when the house docs start to get sick it's a symbol of the whole system getting ill."