In a review of Mr. Mitchum's 1971 film ''Going Home,'' Vincent Canby of The New York Times said the actor had ''reached that point in his career where he doesn't seem to act as much as inhabit whatever film he's in, whatever role he's playing, whether it's an Irish schoolmaster, an Australian sheepherder or, as here, a nice, well-meaning garage mechanic with a talent for bowling.''

The Mitchum image was evident even at the start of his career, when he first generated a world-weary toughness. Audiences' interest was reinforced by tales of his uprooted childhood, adventuresome youth, colorful early jobs, brief imprisonment for vagrancy at age 16 in Georgia, where he was put on a chain gang, and a two-month jailing at 31 in the marijuana case in California.

The drug charge could have destroyed some careers, but at the time it enhanced his image as a rebel. He served 60 days on an honor farm, and in January 1951, after he completed a period of probation, his case was reviewed. After an investigation, a plea of not guilty was ordered and the conviction was expunged from the record. Mr. Mitchum never attempted to publicize his exoneration.

When reporters asked him what jail was like, he replied, ''It's just like Palm Springs without the riffraff.''

Admirers hailed him for infusing flimsy characters with unexpected force, credibility and dignity and for doing laconic wonders with routine phrases. Detractors accused him of appearing sullen, bored and stagey and of relying on a sneaky humor and swagger that approached self-parody. He attributed his trademark sleepy-eyed look to chronic insomnia and a boxing injury that resulted in astigmatism. He once said, ''I agree with the producer who said I looked like a shark with a broken nose.''

A hard-drinking, chain-smoking man who was a colorful raconteur, Mr. Mitchum fielded interviewers' questions with yarns, usually profane and often hilarious. He often tried to rattle questioners with rudeness and sarcasm and sometimes vulgarity.

''When you're successful in the movies,'' he remarked in 1970, ''Hollywood doesn't let you do better. They just let you do more.''

With typical self-deprecation, he said in 1978: ''Half the time you have to have fun with a role. What else is there to do with it? You develop a facility -- and I've had it for a long time -- or you read dialogue that no one else would really dare read. You just have to clean it off your teeth like hen feathers.'' In a more candid moment, however, he acknowledged: ''I like the work. I just don't like talking about it.''

Robert Charles Mitchum was born in Bridgeport, Conn., on Aug. 6, 1917, to James Mitchum, a railroad worker of Irish descent, and Anne Mitchum, the daughter of a Norwegian ship captain. When Robert was 2, his father was killed in a switching accident, and his mother became a Linotype operator to help support her three children.

Robert left school at the age of 14 and made frequent freight-hopping trips around the country, working as a laborer, coal miner, boxer and aircraft assembler. Run-ins with the police gave him a lifelong antipathy to authority.

He and Dorothy Spence, his high school sweetheart, were married in 1940 and lived most of the time in Southern California, while avoiding Hollywood's social scene. He is survived by his wife, of Montecido, Calif.; two sons, James, of Paradise Valley, Ariz., and Christopher, of Santa Barbara, Calif.; a daughter, Petrine, of Burbank, Calif.; a brother, John, of Sonora, Calif., and two sisters, Julie Mitchum of Sonora and Carol Allen of Hendersonville, Tenn.

Resolving on a theatrical career, he acted, directed and wrote in a community theater group in Long Beach, Calif. He entered the movies as an extra and became a skilled horseman to play a string of villains in westerns.

''For a while it looked like I was going to be stuck in westerns,'' he told an interviewer in 1948. ''I figured out I could make 6 a year for 60 years and then retire. I decided I didn't want it. So I started blinking my eyes every time a gun went off in the scenes. That got me out of westerns.'

Robert C Mitchum