Ray Milland, 78, the Welsh-born actor who transfixed movie audiences and belied his debonair image with his wrenching, Academy Award-winning 1945 performance as a despairing novelist on a drunken binge in "The Lost Weekend," died yesterday in California.

Mr. Milland, a naturalized American who had lived in Southern California for years and was a veteran of more than 140 films ranging from "Beau Geste" to "Battlestar Galactica," died at Torrance Memorial Medical Center. His agent said he had suffered from cancer for some time.

A milestone in film history for its treatment of alcoholism, "The Lost Weekend" marked a turning point in Mr. Milland's career. Agonizing and convincing, his performance earned him new regard as a serious, sensitive actor, rather than merely a lighthearted leading man.

Long known for dependability, Mr. Milland went on to such films as "Dial M For Murder" (1954), a Hitchcock thriller in which he teamed with the late Grace Kelly, and "Love Story" (1970), in which he played Ryan O'Neal's father and altered his screen image by displaying his bald pate.

Born Reginald Truscott-Jones in Neath in Glamorganshire, Wales, the future actor spoke only Welsh until the age of 5. After attending private schools in England and Wales, he dropped out of King's College of the University of Wales shortly before joining the British Household Cavalry.

The horsemanship he learned in his four-year stint helped him later in Hollywood, and the marksmanship he developed is credited with winning him his start in movies.

Hired originally by a British company for his ability with a rifle, he was on hand when illness sidelined a featured player, and was in time discovered by Hollywood. His first American picture was "Polly of the Circus," with Clark Gable and Marion Davies.

No instant success, however, he spent time shuttling between Britain and California in search of steady work. At one point, he earned extra money as a steeplechase rider, and appeared in newsreels of one of the most spectacular pile-ups in British racing.

Back in Hollywood in 1934 for the third time, he was about to begin work as the $27.50-a-week manager of a Sunset Boulevard service station when he signed a two-week contract with Paramount Pictures to substitute in "Bolero" for another British actor who had been injured.

A multiyear contract followed. Through the late 1930s and early 1940s, Mr. Milland showed his easy smile and pleasant manner as a cowboy, playboy or aviator, or occasionally as a fop, in westerns, romances, costume dramas and melodramas.

For his role in "The Lost Weekend," Mr. Milland pared his 6-foot-2 frame to 160 pounds and spent a night with New York bums to help him play Don Birnam, the dipsomaniac writer who made screen history with his stumbling journey up New York's Third Avenue in a desperate, doomed attempt to pawn his battered typewriter.

A well-received 1974 autobiography told of his own intolerance for liquor, as well as of pre-screen days in Britain's provincial theater, and of later life in the international set.

It also showed a cool,complex man who struggled to appear at ease in his roles, questioned his fitness for acting, and was subject to "that niggling feeling that I was being an emotional prostitute."

Survivors include his wife and a daughter.