A Bethesda-based citizens group urged the Nuclear Regulatory Commission yesterday to deny the Defense Department a renewal of its 20-year license to use a large quantity of a radioactive element at the National Naval Medical Center in Bethesda. A lawyer for the group, Citizens for Nuclear Reactor Safety, Inc., said there have been accidents at the facility and that lives of nearby residents could be endangered.

"We have a situation of compounded risks here," said attorney Elizabeth Entwisle. "The cobalt-60 irradiator is sitting in a building with a nuclear reactor facility and sitting in Bethesda, Maryland. The question would be moot if the cobalt were in a desert."

Lawyers for the Defense Department and for the technical staff of the Nuclear Regulatory Commission argued that the license should be renewed, saying there have been no accidents at the facility, only "incidents" that could not harm anyone. "I don't see what issues they're raising," said David Rickard, deputy general counsel for Armed Forces Radiobiology Research Institute.

Scientists at the medical center use cobalt-60 in research on animals, to determine the effects of nuclear weapons on people, according to a report by the institute, the division of the Defense Department that conducts the research. There are 94,000 curies of cobalt-60 in a room on the ground floor of the center. Most hospitals have on hand 5,000 to 10,000 curies of cobalt-60 for medical purposes, while research facilities throughout the country use several hundred thousand curies each, institute officials said.

About 30 Montgomery County residents, most of them women, attended the hearing in the Bethesda headquarters of the NRC.

The residents organized shortly after the Three Mile Island nuclear reactor accident to investigate whether there were nuclear reactors in the metropolitan area, Entwisle said. They found several, one of them at the Bethesda Naval Center. Soon afterwards, they gathered documentation to protest the renewal of the reactor's license, and they are still protesting. Last year, the group learned that the cobalt-60 facility also was up for a license renewal.

The hearing yesterday was to determine whether there are sufficient reasons for the NRC to hold a hearing to consider denying a renewal of Defense's license to operate the cobalt-60 irradiator in Bethesda.

Entwisle argued that several accidents connected with the cobalt irradiator pointed out the danger of having such a facility in Bethesda. In one, on Nov. 11, 1976, water from a broken pipe flooded the cobalt irradiator, according to internal documents obtained by the citizens group. Officials then pumped the water, about 50,000 gallons, into the county sewer system, which eventually travels into residents' water supply, Entwisle said.

"They've made self-serving statements that the water was below radioactive levels," said Entwisle. "I would like to see corroboration by local and state officials."

Rickard, counsel for the institute, said that the levels of radioactivity in the water were extremely low and not dangerous.

In the other accident, which Entwisle said occurred on April 22, 1981, the elevator system responsible for raising the cobalt-60 from the water where it is stored malfunctioned. As a result, the cobalt-60 was exposed to the air for more than three weeks, when center officials obtained a robot named Herman that fixed the elevator and restored the cobalt-60 to the water.