A federal judge ruled yesterday that the National Weather Service is liable for the deaths of three fishermen in a fierce storm that forecasters failed to predict.

U.S. District Court Judge Joseph Tauro in Boston found that the agency was negligent in failing for more than three months to maintain a weather buoy that could have predicted the 1980 storm.

Michael Latti, attorney for the plaintiffs, said he did not think the ruling would expose the government to lawsuits over deaths or injuries caused by snowstorms, tornadoes, floods and other foul weather that the service failed to predict.

The difference in this case, Latti said, is that the government encouraged fishermen to rely on its weather buoy in the Georges Bank fishing area, "then pulled the rug out from under them without giving them a warning."

Weather service spokesman Don Witten said the government probably would appeal. "Our argument is that there was no negligence by the National Weather Service in this case, either in the formation of the forecast or the maintenance of the buoys," he said.

Latti is representing relatives of William Garnos, 30, David Berry, 20, and Gary Brown, 25, all lost at sea when their small lobster boats were caught in the November 1980 storm. Latti said he introduced documents showing that some federal officials were concerned that the weather buoy, about 150 miles off Massachusetts, had been transmitting inaccurate and incomplete data for months.

A separate trial will be held next month on damages.