Mercedes McCambridge, who won an Oscar for the 1949 film ''All the King's Men'' and later provided the raspy voice of the demon-possessed girl in ''The Exorcist,'' died in the La Jolla area of San Diego on March 2. She was 87 and had lived in La Jolla since the 1980's.

Ms. McCambridge died of natural causes, said Cathy Ruppert, the assistant to the trustee of the actress's estate.

A strong, radio-trained voice made Ms. McCambridge an ideal portrayer of hard-driving women. She received the Academy Award as best supporting actress for her screen debut in ''All the King's Men,'' in which she played a reporter who was the nemesis of a populist Southern governor, Willie Stark.

Broderick Crawford was named best actor for his role as Stark, who closely resembled Gov. Huey Long of Louisiana, and the movie received the Oscar for best picture.

Ms. McCambridge acquired a reputation as a strong-willed, outspoken woman on and off the screen. When she was hired to play the enemy of Joan Crawford in a 1954 Western, ''Johnny Guitar,'' the two feuded on the set. In her memoir, Ms. McCambridge called Crawford ''a mean, tipsy, powerful, rotten-egg lady.''

Because of her great vocal skills, Ms. McCambridge was hired to portray the Demon in William Friedkin's 1973 smash hit ''The Exorcist.'' After weeks of what she called the hardest work she had done for a film, she was promised prominent mention in the credits.

But when she attended the preview, her name was missing. As she left the theater in tears, Mr. Friedkin tried to explain that there had been no time to insert her credit. The Screen Actors Guild intervened and forced her inclusion.

Despite the celebrity that followed her Academy Award for ''All the King's Men,'' Ms. McCambridge's film career did not flourish. Because she did not fit the glamour-girl image that was prevalent in postwar films, movie offers were sporadic.

Among her later films were ''Giant'' (1956), for which she received her second Oscar nomination as best supporting actress; ''A Farewell to Arms'' (1957); ''Touch of Evil'' (1958), which starred her radio associate Orson Welles; ''Suddenly Last Summer'' (1959); ''Cimarron'' (1960); ''99 Women'' (1969); ''Thieves'' (1977); and ''The Concorde -- Airport '79'' (1979).

In the early 1990's, Neil Simon called with an offer to play the grandmother in ''Lost in Yonkers'' on Broadway and on the road. It proved to be a triumph for her, and she performed the play 560 times.

In her later years, Ms. McCambridge also appeared in ''Magnum, P.I.'' and other television series, but her movie work was sparse.

''I don't think the Hollywood community is interested in what I can do,'' she said in a 1981 interview. ''That's all right. I've never looked for a job in my life, and I'm not going to start now. I have plenty to keep me busy.''

Charlotte Mercedes Agnes McCambridge was born on March 16, 1916, in Joliet, Ill., Ms. Ruppert said. She began giving her birth date, though, as St. Patrick's Day 1918. In explaining the discrepancy, Ms. Ruppert said, ''She's an actress,'' adding: ''She was a little bit Irish. And she decided she wanted to be two years younger.''

After graduation from Mundelein College in Chicago, she acted in Chicago radio, which then produced several network soap operas and nighttime shows. She married her first husband, William Fifield, at 23.

They eventually wound up in Hollywood, where she resumed her career as a radio actress. Her vocal versatility brought her jobs on shows that ranged from ''I Love a Mystery'' to ''Red Ryder.''

Ms. McCambridge returned to New York for the title role in a radio adaptation of the play ''Abie's Irish Rose.'' She later found steady work in Welles's radio dramas; he called her ''the world's greatest living radio actress.''

From 1950 to 1962 she was married to Fletcher Markle, a Canadian-born radio director who became well known in the United States in the years of live television drama. During the marriage and afterward, she was sometimes hospitalized after episodes of heavy drinking. She was able to stop drinking with the help of Alcoholics Anonymous.

Ms. McCambridge battled through much of her life, surviving not only alcoholism, but also two failed marriages and tragedies involving her only child, John Lawrence Fifield. The son, who later took Mr. Markle's surname, killed his wife and children and then himself in 1987.

Mercedes Mccambridge