Rebecca West, 90, one of the most admired and provocative English writers of the modern age, died yesterday at her home in London. The cause of death was not reported.

Miss West was a writer of enormous range and sensibility. She wrote criticism, essays, novels, history, journalistic pieces and autobiography. Her subjects included the causes of women, common murder and high treason, the value of life, and important, psychologically acute, portraits of D.H. Lawrence and Henry James.

She was a feminist, a one-time socialist and a free spirit who in 1914 bore a child out of wedlock by H.G. Wells. Until the end of her life she was famously witty and her remarks could be dangerously barbed. In 1930, she confounded many of her admirers by marrying Henry Maxwell Andrews, a lawyer and banker, and lived happily with him in a lovely house in Buckinghamshire until his death in 1968. In 1949, she was made a member of the Order of the British Empire and in 1959 she was made a dame of the same order.

As artist and woman, she defied categorization.

Yet there is substantial agreement that "Black Lamb and Grey Falcon," a two-volume work on Yugoslavia that appeared in 1941, is a masterpiece; that her novels "The Fountain Overflows" and "The Birds Fall Down" have found a permanent place in letters; and that her reportage on treason trials after World War II, much of which appeared first in The New Yorker, set the style of the New Journalism, in which informed speculation as to motive is used to illuminate the facts of the matter.

Her pieces on war crimes and treason--she covered part of the Nuremberg trials, including that of William Joyce, who broadcast for the Nazis and who was called "Lord Haw-Haw"--were published in 1947 as "The Meaning of Treason." A revised version appeared in 1977 under the title "The New Meaning of Treason."

Miss West published three books in 1982: "The Return of the Soldier," her first novel, which originally appeared in 1918; "Harriet Hume," a novel which was written in 1929; and "1900," a new autobiographical sketch that is richly illustrated with photographs. An anthology edited by Jane Marcus, "The Young Rebecca: Writings of Rebecca West 1911-17," also was published last year.

In her last year or so, Miss West played a cameo of herself in "Reds," the Warren Beatty film about John Reed and the Russian Revolution, gave a lengthy interview to The Paris Review, continued her work as a book reviewer, and worked on a novel. In an interview with Vogue magazine recently she said:

"I do not myself find it agreeable to be 90. It is not that you have any fears about your own death, it is that your upholstery is already dead around you."

In an interview with The New York Times in 1978, she said that Watergate was an important event, but deplored the way people "roll their tongues" about it. "In a lot of ways, Nixon was not stupid," she said. "He was an example of bad form combined with Original Sin."

And in 1911, when she was on the staff of The Freewoman, a feminist journal that her mother would not permit in her house, she wrote: "I myself have never been able to find out precisely what feminism is. I only know that people call me a feminist whenever I express sentiments that differentiate me from a doormat or a prostitute."

Her friend George Bernard Shaw once said, "She can handle a pen as brilliantly as ever I could, and much more savagely."

Miss West was born in County Kerry, Ireland, on Christmas Day, 1892, and named Cicily Isabel Fairfield. She grew up in Edinburgh, where she attended George Watson's Ladies' College. She also attended the Royal Academy of Dramatic Art in London. She had a brief career on the stage that included a part in Ibsen's "Rosmersholm," one of whose characters is named Rebecca West. That became her pen name.

As a young woman, she was a member of the Fabian Society, an early cornerstone of British socialism. She left it, apparently because of a dispute with Beatrice and Sydney Webb, its founders. Her first book was a study of Henry James and she argued that he had "refused to dramatize in his imagination anything concerning women save their families and successes as sexual beings."

"The Return of The Soldier," her first novel, is about a young man who comes home from the front in a state of shellshock and amnesia. His wife, his sister and his first love are in a quandary over whether to try to cure him. For if they do, he will have to go back to the war. In a passage that expresses Miss West's own view of the world, the heroine says at the end:

"There is a draught that we must drink or not be fully human . . . . I knew that one must know the truth. I knew quite well that when one is adult one must raise to one's lips the wine of truth, and celebrate communion with reality, or else walk forever queer and small like a dwarf."

Miss West is survived by her only child, the critic and writer Anthony West.