Doctors whose testimony does not pass muster can be suspended or expelled from the societies.

Lawyers who represent those suing doctors in malpractice cases say such reviews and the threat of sanctions are meant to intimidate witnesses. They say the mere existence of the reviews has made it harder to find experts, whose testimony is crucial in most malpractice trials.

The idea for the grievance review seems to have started with the American Association of Neurological Surgeons, which has prevailed in three court battles over their legality. Societies of obstetricians, gynecologists and spine doctors followed, and societies of anesthesiologists and ear, nose and throat specialists are expected to vote on establishing similar procedures this summer and fall.

"There are probably another 10 that are studying it closely," said Russell M. Pelton, a lawyer in Chicago who represents the neurosurgeons' association.

The American Medical Association supports the moves, said Dr. Donald J. Palmisano, the association's president-elect.

"The giving of expert testimony should be considered the practice of medicine, and it should be the subject of peer review," Palmisano said. "If someone comes into court and gives junk science, we don't want fraudulent testimony in court."

But the trend troubles plaintiffs' lawyers.

"Not only does this appear to be a form of intimidation of witnesses that violates the federal Civil Rights Act, but this is a sort of restraint of trade that could also be an antitrust violation," said Robert Peck, the president of the Center for Constitutional Litigation, which often represents the American Trial Lawyers Association.

"It's extremely widespread," Peck said. "It leads us to believe that many doctors are afraid to come forward because they fear retaliation."

Some lawyers say the effect of the grievance procedures is already being felt in the legal system.

"It's more difficult to get a good neurosurgeon as an expert than any other specialty," said Norman D. Tucker, a Michigan lawyer who represents patients.

Dr. Albert L. Strunk, vice president for fellowship activities at the American College of Obstetricians and Gynecologists, said he was not convinced that review of expert testimony by medical societies would prevent poor- quality testimony. The college has a grievance program that has heard occasional complaints about such testimony.

"When a medical society disciplines one of its members for this sort of thing, it just plays into the hands of the personal injury lawyers," Strunk said. "They say this is the medical profession closing ranks to stifle doctors who are speaking out on behalf of a patient who has been injured."

The neurosurgeons' association has heard more than 30 complaints over the past 20 years, all but one of them about expert testimony given on behalf of plaintiffs, Pelton said. Only members of the society can file a grievance.

The hearings resemble trials, with witnesses and lawyers. They are usually conducted during annual conventions. The doctor bringing the complaint must prove "unprofessional conduct, not a difference of opinion between professionals," Pelton said. "Due process is observed."