Mary Tyler Moore's only son, 24-year-old Richard Meeker, killed himself with a shotgun blast to the head late Tuesday night at the home he shared with two young women near the University of Southern California campus, police said yesterday.

Investigators conducted an autopsy yesterday, but the coroner's report was not released, and police said that a coroner's investigation would be necessary to determine whether the death was suicide or an accident.

In her latest movie, "Ordinary People," Mary Tyler Moore plays a mother who loses one son in an accident and almost loses the other in a suicide attempt.

Meeker, Moore's son by her first marriage, was reportedly "playing with a sawed-off shotgun" and talking to a roommate at the time of the shooting.

The roommate, Judy Vasquez, 21, was quoted by Detective Jerry Ferrin as saying, "He was loading and unloading the short-barreled gun when it went off . . . It was awful. He must have pulled the trigger. There was a big bang and he fell on the bed." The other roommate, Janet McLaughlin, 23, was in another room of the house at the time.

Her son's death marks the second time in two years that tragedy has struck Moore's life. Her sister, Elizabeth Ann, died of a drug overdose in 1978 at the age of 21. The Los Angeles County coroner's office ruled the death a suicide, although Moore has contended that her sister did not kill herself.

The first indications from Meeker's roommates were that the shooting was accidental. McLaughlin said she had spent the entire evening with him and he showed no signs that would lead her to believe he wanted to kill himself. He made several telephone calls, including one to his girlfriend in Fresno, Calif., and his mood never darkened, she said.

McLaughlin said Meeker kept the short-barreled .410-gauge weapon in an accessible place because of his concern about burglars.

After the shooting, producer Grant Tinker, Moore's estranged second husband, was notified. He in turn called Moore in New York City.

"I waited a couple of hours so the shock wouldn't come in the middle of the night," Tinker said. "Richard was a good guy. Calling Mary was the most difficult thing I ever had to do." He said the news "absolutely destroyed her." Moore returned to Los Angeles immediately.

Meeker's father, a television account executive in Sacramento, was called to the scene early yesterday, according to Detective Sgt. Eugene Clarke.

McLaughlin, a student at USC, told police that in their conversation that evening, Meeker "said he was bored, but it was a remark just in passing. He didn't mean anything by it.

"He said everything was all right and that he was happy with his job [as a messenger for CBS]. We even discussed fixing up the house we had rented."

She said that after Vasquez returned home from a class, the three of them talked as they moved about the house.

"I asked him how his day went and he said, 'fine,' and we spoke a few more words," Vasquez said. "I heard the gun click and it went off."

"He talked to his mother on the telephone [earlier in the day]," said Detective Ferrin. "At no time did he seem despondent, and there were no indications that he intended to kill himself."

Meeker was rarely photographed with his famous mother and reportedly was purposely sheltered from publicity.

Psychologists over the years have said that having famous parents in any field is a burden to children, often causing emotional problems.

In recent years, the children of Gregory Peck, Dan Dailey and James Arness took their lives. Jonathan Peck, 30, shot himself to death more than three years ago. Dan Dailey III was 27 when he turned a pistol on himself.In 1975, Jenny Arness, 20, died of an overdose of sleeping pills.

One of Meeker's superiors at CBS said he was a normal, well-adjusted young man, adding, "Nobody will ever make me believe his death was anything but an accident."

Another friend of Meeker's said he collected and enjoyed guns and target shooting.