Medical investigators have found signs of lung damage - probably from exposure to asbestos - in about 600 of slightly more than 1,000 long-time employees examined at General Dynamics' Electric Boat division in Groton, Conn.

General Dynamics used asbestos as an insulating material in its ships until several years ago. It stopped as evidence accumulated that asbestos causes various kinds of damage, including cancer, in the lungs and abdomen of those exposed.

The tested empolyees almost all have worked at the boat yard 15 years or longer.

Few of the employees tested worked directly with asbestos, but they were exposed to significant concentrations of asbestos fibers in the air inside the ships they were building.

The testing was done over the last two years by doctors from the Environmental Sciences Laboratory of the Mt. Sinai School of Medicine in New York, under auspices of the federal government's National Institute of Environmental Health Sciences.

Lung X-rays showed signs usually associated with asbestos damage in about 600 of the workers, sources said.

The findings have been presented to both the Pipefitters union, which represents some of the boat yard workers, and the company. What will come of the findings is not yet clear.

It generally takes 15 to 20 years for the damaging effects of asbestos to become apparent in an exposed worker.

One knowledgeable doctor said yesterday that studies in other countries have found "a great deal of cancer . . . among former and older shipyard workers," apparently from asbestos exposure.

The Groton study suggests that a similar pattern may prevail in this country. Tens of thousands of workers have been employed at the Groton boatyard over the years, a doctor noted.