There were nights that Lily Grubb, alone in her red-brick home, lay awake and wondered how her husband of 45 years could have died so suddenly after a heart operation at Bethesda Naval Hospital. Then, last week, Rear Adm. William M. McDermott Jr. told her something that ended the wonder and moved her to call her son in a daze.

"I believe he said Dr. [Donal M.] Billig killed your father," the 67-year-old widow remembers saying to Bill Grubb after a phone call from McDermott. In a few hours, after he had made a few more calls, Bill Grubb had the answer: "Mom, you're right."

Lily Grubb, a soft-spoken grandmother of five and a nurse-anesthetist, answered questions quietly today in an interview at the airport here. She was one of a group of people told by the Navy in the past week that their relatives may have died at the hands of Cmdr. Donal M. Billig, the former head of heart and chest surgery at Bethesda and a surgeon who the Navy has charged with involuntary manslaughter in connection with four deaths there.

The Navy, which has refused to release the names of the four people it said died in Billig's care, confirmed today that Billig operated on retired Army Maj. William Franklin (Frank) Grubb Jr., 73, on Aug. 8, 1984.

The Navy also confirmed today that McDermott, who ordered an investigation of Billig's competence as a surgeon, made a telephone call to Lily Grubb on June 19. That was the same day the Navy announced the charges against Billig, recommended him for general court-martial and disclosed that the investigation had revealed the heart surgeon was suffering from a severe loss of sight in his right eye.

Navy officials would not confirm today that Grubb was told that her husband, a 30-year Army veteran, was one of the four people whose deaths prompted the manslaughter charges.

McDermott was out of town and could not be reached for comment, but Navy sources said Grubb was one of the four Bethesda patients involved.

The Navy also would not release details about 22 other heart operations that have been used as a basis for dereliction of duty charges against Billig. Billig worked at the hospital, one of the Navy's premier medical centers, from January 1983 through November 1984.

Contacted today through his attorney, Billig would not address queries about Grubb. Billig, 54, said he "did not wish to answer any questions" about the charges he faces, Lt. Neil Worden said.

Lily Grubb, in an interview here just a few miles from her South Carolina home, broke down in tears as she gave this account of when she first heard her husband may have died needlessly.

She had just gotten home from a leisurely lunch with a friend when the phone rang. The man on the other end of the line identified himself as an Admiral McDermott. "He verified who I was and then said was I aware Frank had been at Bethesda and was I aware that Dr. Billig was his surgeon.

Grubb said McDermott told her he was bringing charges against Billig for four deaths including her husband's. "I couldn't believe it," Grubb said yesterday. "I couldn't believe I heard him right. Then he said: 'I'm telling you to get a lawyer and I'm giving you permission to sue the government.' "

Active duty members of the armed forces cannot sue the government for injuries incurred during service, and neither can their families on their behalf, according to federal law. Grubb, however, can sue because her husband was retired at the time of his operation.

Navy officials said today that the Navy "is not likely to contest liability" in the cases they have cited as their basis for court-martial.

If that decision becomes firm, Grubb, who has retained Washington attorney Robert R. Smiley as counsel, would not have to prove that the Navy is responsible for her husband's death. Rather, she would have to prove how much compensation she should receive for the loss of her mate. "It becomes a numbers game," according to a Justice Department source familiar with the case.

That compensation may do little to ease the pain that Lily Grubb experiences when she recalls the unexpected death of her high school sweetheart from Haddonfield, N.J.

Drafted into the Army just before World War II, Frank Grubb had served in the infantry during the Battle of the Bulge and returned to the battlefield a few years later in Korea. Another overseas assignment sent him to Germany and Lily and their two children followed. His last 11 years were quiet ones in Annandale, where he worked for a nearby Army map service in a security position, Lily Grubb said.

He retired from the Army in 1972 and began working for a private computer company. He suffered a heart attack shortly after, though, and the couple decided to retire to South Carolina.

Over the years, Frank Grubb's health deteriorated. He began taking medication for angina attacks that grew worse. On July 23, 1984, he went to Bethesda Naval Hospital, the hospital his family had used in the years they lived in Virginia, for some outpatient tests on his heart, Lily Grubb said.

"We went to Bethesda because it is supposed to be a good hospital and it was convenient -- just off the Beltway . . . Frank wanted to go there because he was worried about a high medical bill and knew the military would pay for it all. He said he was eligible for military care, the military had good medicine and he wanted to go there," Grubb said.

About a week later, Lily Grubb met Billig, the doctor who told her he had looked at the preliminary tests, found her husband's heart muscle was strong and thought an operation to eliminate arterial blockage -- a triple bypass -- would cause no problems. "He told me Frank had the heart of a 40-year-old . . . and there was no reason for him not to have the surgery and do well, " she said.

Lily Grubb never spoke to Billig again. After the operation and after her husband died, she said, Billig never approached her. Grubb said that McDermott told her that Billig was the primary surgeon at her husband's operation.

Lily Grubb saw her husband go into surgery at 4 a.m. on Aug. 8. At 1:30 p.m., a doctor came from the recovery room and told her that Frank Grubb was fine. At 4 p.m., she saw her husband and he raised his eyebrows. At 6 p.m., she saw him and he fluttered his eyes. At 8:30 p.m., Grubb looked at her husband, called out his name and "I got absolutely no response," she said in the interview.

Nervous, she called to a nurse. Within a half hour, as Grubb was standing next to her husband's heart monitor, she heard it buzz and saw a straight line go across the screen.

At 11:15 p.m., she was told her husband was dead.

The death certificate that Grubb keeps at home states that her husband died from cardiac arrest due to a coronary bypass. She said that an autopsy report shows that one artery that supplied the heart was devoid of blood.

"I questioned that when I first saw it but I could never bring myself to write a letter," she said. Grubb said she mentioned it to McDermott last week. He told her that "I was exactly right . . . but he didn't tell me what I was right about," she said.

Grubb fills her days now by resuming some nursing duties at a local hospital. Somberly touching a diamond crucifix that her husband gave her, she said she hasn't stopped thinking in the past week about the way his death could have been avoided.

"Questions have to be asked about competence," Grubb said. "I'm sure the military doesn't like to answer those questions, maybe because they assume that you have enough confidence in them that they will choose the right people . . ."

"I really believe people -- if they're Christians -- are used to accomplish a purpose. I think: Was Frank used in a blatant way to help bring this man to justice? Obviously, it was going on and on and Billig was not being brought to justice.

"I have to believe there was a reason."