Cmdr. Donal M. Billig, the former head of heart and chest surgery at Bethesda Naval Hospital, has been charged by the Navy with a fifth death in connection with his work at the hospital from January 1983 through November 1984.

The additional involuntary manslaughter charge, stemming from the death of John L. Kas Jr. on Oct. 29, 1984, was disclosed yesterday at a pretrial proceeding for Billig, who is facing a general court-martial in connection with his surgical practices.

Navy officials were unable to supply additional information about Kas' death or his service background. Military papers filed against Billig in the Kas case, however, charge that he was the supervising surgeon or first assistant during a heart operation in which a cardiac vent was improperly repaired, a vein was improperly grafted, and the heart was overmanipulated.

Billig, 54, had been recommended for court-martial and charged by the Navy with four counts of involuntary manslaughter and 24 counts of dereliction of duty for heart operations he performed at Bethesda in 1983 and 1984. Those charges were handed down in July after a formal investigation was begun.

The latest charge, according to Navy spokesmen, resulted from additional research by Navy investigators.

The disclosure was made yesterday shortly before testimony began in the second day of a pretrial investigation against Billig. During yesterday's proceedings, which focused on another case, a Bethesda Naval Hospital anesthesiologist who assisted Billig during a flawed and fatal heart operation in November 1984 said he "couldn't find fault" with the heart doctor's procedure, although Billig inadvertently tore the patient's aorta.

Lt. Commander Joseph Coyle, the assistant head of the intensive care unit at Bethesda Naval Hospital, recounted the operation of Lois Parent, the wife of retired Marine Sgt. Maj. Maurice Parent and one of four patients whose deaths prompted the original involuntary manslaughter charges against Billig.

"It was as much -- it was even more -- operating risk than clumsiness," Coyle said about the tear. He later added, "I think you'd have to say it was the tear to the aorta that initiated the cascade of events" that led to Parent's death.

The charge involving the Parent death claims that Billig was negligent when he operated Nov. 2, 1984, on Lois Parent by tearing her aorta, improperly attempting to repair the tear and improperly placing her on the bypass machine during the course of the operation. That operation was the focus of yesterday's hearing.

Coyle, one of 10 witnesses scheduled to testify this week at the Navy Yard, described Billig as a very concerned physician, a good thoracic surgeon and an able administrator. When Coyle's father needed bypass surgery, Billig was one of the doctors in the operating room, Coyle said.

Parent had had two previous heart operations, and her aorta was found to be scarred, Coyle said. The aorta tore as Billig attempted to clamp off the blood supply, he said.

"He was appropriately alarmed," Coyle said. Attempts to repair the aorta were hampered because of the delicate nature of the previously scarred tissue, he said.

"Do you think anything that happened to Lois Parent constituted criminal negligence?" asked defense attorney Lt. Neil Worden.

"No, personally I didn't feel that," Coyle said.