Beatrice Straight, a graceful and versatile actress who won both an Oscar and a Tony Award, died on Saturday in North Ridge, Calif. She was 86 and lived in Beverly Hills, Calif., for most of the last 10 years.

Because she came from a wealthy family, the Whitneys (her mother was Dorothy Payne Whitney), she never had to act for a living but was dedicated to the art of theater. When she became successful, she continued to choose roles for their challenges rather than for their ability to further her career.

Onstage and in films, Ms. Straight projected an image that was dignified but with strong emotional undercurrents. She brought believability to whatever role she undertook, acting in classics as well as contemporary plays and movies.

In the original Broadway production of Arthur Miller's ''Crucible'' in 1953, she was the essence of Elizabeth Proctor. Reviewing the play in The New York Times, Brooks Atkinson said that both Ms. Straight and her co-star, Arthur Kennedy, were superb, adding that in performance, she was ''reserved, detached, above and beyond the contention.'' That role earned her a Tony as best supporting actress.

In 1977 she won an Academy Award as best supporting actress for her performance in Sidney Lumet's ''Network'' as the wife William Holden's character spurns. The role was brief but noticeable, behind the dramatic fireworks, a familiar place for Ms. Straight.

She had a variety of roles in plays by Shakespeare, Shaw, Chekhov, Ibsen and Tennessee Williams. In 1982 she scored another film success in ''Poltergeist'' as a psychologist moonlighting as a parapsychologist.

Beatrice Whitney Straight was born in Old Westbury, N.Y. Her father, Willard Dickerman Straight, was a banker and former official in the State Department. She attended the Lincoln School in New York and Dartington Hall Community in Devonshire, England, a school founded by her mother and stepfather, Leonard Elmhirst.

She made her Broadway debut in 1935 in ''Bitter Oleander.'' After she persuaded Michael Chekhov, Chekhov's nephew, to join her in forming an acting school and company, the Dartington Hall Players in England, they brought the troupe to the United States, where she performed in Shakespeare. Then she continued on Broadway as Olivia in ''Twelfth Night,'' Emily Dickinson in ''Eastward in Eden'' and Lady Macduff in ''Macbeth,'' with Michael Redgrave.

In 1948 she succeeded Wendy Hiller as Catherine Sloper in the Broadway production of ''The Heiress,'' an adaptation of Henry James's ''Washington Square'' in which she played opposite Peter Cookson. After the run, she and Mr. Cookson married. It was a second marriage for both.

In 1950 Ms. Straight played the governess in ''The Innocents,'' an adaptation of James's ''Turn of the Screw'' produced by Mr. Cookson. In his Times review, Mr. Atkinson said that Ms. Straight acted ''with force, sensitivity and old-fashioned charm, in a style that Henry James would have been compelled to applaud.''

She continued to act on and off Broadway, playing opposite Richard Kiley in Robert Ardrey's ''Sing Me No Lullabies'' and opposite Van Heflin in the Broadway version of Rod Serling's television play ''Patterns.'' She also had the title role in Racine's ''Phèdre.''

In 1967 she was in ''Everything in the Garden,'' Edward Albee's adaptation of a play by Giles Cooper. In 1973 she played Mrs. Alving in a Roundabout Theater production of Ibsen's ''Ghosts'' and in 1979 was Gertrude to William Hurt's Hamlet at the Circle Repertory Company.

Among her many television appearances, she was Goneril to Orson Welles's King Lear in an abbreviated version of the play on ''Omnibus,'' and Rose Kennedy in ''Robert Kennedy and His Times.'' In 1986 she was in Mr. Lumet's film ''Power'' and in 1991 played Goldie Hawn's mother in ''Deceived.''

Throughout her life, Ms. Straight was also a producer and teacher. As a founder of Theater Incorporated, she was instrumental in bringing the Old Vic, with Laurence Olivier and Ralph Richardson, to the United States. In 1981 she helped revive Michael Chekhov's School of Theater in New York.

Ms. Straight's husband died in 1990. She is survived by her sons, Gary Cookson, an actor in New York, and Tony Cookson, a writer and director in Santa Monica, Calif.; two stepchildren, Peter Cookson Jr. of Irvington, N.Y., and Jane Coopland of Hawaii; a brother, Michael Straight of Chicago, a former deputy chairman of the National Endowment for the Arts; seven grandchildren; and three great-grandchildren.

Despite her patrician background, Ms. Straight always regarded herself as a working actress. ''I may have been born in society,'' she once said, ''but I was never part of anything but theater.''