Tennessee Williams, 71, one of America's leading playwrights, was found dead yesterday in his room at the Elysee Hotel in New York City. The cause of death was unknown pending completion of an autopsy.

Mr. Williams' principal works included "The Glass Menagerie" (1944), "A Streetcar Named Desire" (1947) "Cat On a Hot Tin Roof" (1954) and "The Night of the Iguana" (1961). These brought him not only enormous success with the public, but the unstinting praise of critics. He won two Pulitzer Prizes, four Drama Critics Awards, the Gold Medal of the National Institute of Arts and Letters and the Medal of Freedom, which was conferred on him by President Jimmy Carter in 1979.

"He was the greatest American playwight. Period." This accolade came from Walter Kerr, a drama critic of The New York Times. Writer Eudora Welty called Mr. Williams "about the only original playwright we had." Arthur Miller, himself a Pulitzer-Prize-winning dramatist, said, "To his everlasting honor, he persevered and bore all of us toward glory."

Mr. Williams was a Southerner by birth and the South provided the setting and characters of much of his work, which included poetry, short stories, a personal memoir and a novel in addition to numerous plays. Yet his themes transcended the region he portrayed. His characters face contradictions between reality and fantasy. They cannot reconcile them and this failure arises from their humanity.

In "Streetcar," the vulnerability and pretension of Blanche DuBois lead to her disintegration. In "Glass Menagerie," the pretentious and vulnerable Amanda Wingfield tries to arrange a marriage for her daughter, who is obsessed with a collection of glass animals. "Night of the Iguana" is a study of loneliness set in a rundown hotel overlooking a rain forest in Mexico. Sex and perversion, cannibalism, incest and Christianity, cancer and mental illness, the harshest reality and the most macabre fantasy--these are facts in the lives of Mr. Williams' characters.

Although Mr. Williams had not had a major success since "Night of the Iguana," his work continues to be performed by repertory companies and at festivals. Some of his characters are as prized by actors and actresses as they are by the filmgoers and theatergoers who are moved by them. Marlon Brando made his reputation as the crude Stanley Kowalski in "Streetcar" and ever after acknowledged his debt to the writer.

"What has kept the theatergoer interested through the years . . . is Mr. Williams' superb theatrical talent," the critic Stanley Kauffmann has written. "His eye for stage effect, his skill in scene construction, his gift for dialogue that can cut to the bone, that can use cliche with humor and poignancy, and that can combine the odd floridness of lower-class characters with his own rich rhetoric . . . . "

Mr. Williams lived in Key West, Fla., for many years. His habit was to rise before dawn and to work at an old typewriter. Despite personal vicissitudes that included nervous breakdowns, dependence on drugs and alcohol, homosexuality and, in recent years, scant acclaim from critics, he continued to write until the end of his life.

"I am not in the habit of retreat," he used to say.

Of his work he said: "All organic writing is autobiographical; you cannot write about an emotion unless you have experienced it."

Mr. Williams was born on March 26, 1911, at Columbus, Miss. His father was Cornelius Coffin Williams and his mother was Edwina Dakin Williams. He was the second of three children, the others being Rose Williams and Dakin Williams. He was christened Thomas Lanier Williams. His father apparently was a rough-cut man who enjoyed, by the account of his wife, "long poker games and drinking bouts." His mother was the daughter of an Episcopal minister and held traditional notions of proper behavior.

The family moved to St. Louis when Mr. Williams was about 12. His father worked for the International Shoe Co. Rose began collecting glass animals. In 1934, she underwent a lobotomy and for the rest of his life Mr. Williams saw to her care in a sanitarium.

By the time he entered the University of Missouri in 1931, Mr. Williams already was writing. In 1933, he dropped out of college and went to work for the shoe company. He wrote at night. His work met little success and he had a nervous breakdown. He later took to the road and supported himself with odd jobs. He attended the University of Washington and eventually received a degree from the University of Iowa. During this period, he took the name Tennessee Williams, apparently because he was so dissatisfied with the early work that he had published under his given names. His father's family had been pioneers in Tennessee.

His first success came when he received a Rockefeller fellowship. This enabled him to write "Battle of Angels," a play about repressed sexuality and religion in a southern town. The work so outraged audiences in Boston that it never got to New York. (In 1957, after some rewriting, it was performed in New York as "Orpheus Descending" and met an indifferent reception).

After more drifting, Mr. Williams went to Hollywood for a six-month stint as a scriptwriter. He produced "The Gentleman Caller." When his contract was not renewed, he converted this into "The Glass Menagerie." It opened at the Playhouse Theater on Broadway on March 31, 1945, and was an unqualified hit. The New York Drama Critics Circle named it the best play of the year.

In 1979, Mr. Williams told an interviewer that he no longer cared to see "The Glass Menagerie" because "it reminds me rather painfully of my mother. She never understood how much of her was Amanda."

In 1963, Frank Merlo, who had been Mr. Williams' companion for 14 years, died of cancer. The writer went into a decline marked by drink and drugs and ending with a nervous breakdown. In a widely quoted remark, he told the writer Gore Vidal that he had slept through the 1960s. "Well, you didn't miss a thing," Vidal is said to have replied.

Mr. Williams also underwent a period of psychoanalysis and this helped him to come to terms with the memory of his father. Analysis showed him, he said, "that my father was a victim" and that he must forgive him if he meant to come to terms with life.

As for his mother, analysis showed that she "was the strong one. She is the one who approved the lobotomy for Rose . My sister had been away at a school for girls, All Saints School, and when she came home she talked about how the girls stole candles from the chapel and committed self-abuse. My mother wanted her to stop saying all those terrible things, just like Mrs. Venable, the aunt in 'Suddenly Last Summer.' My mother wanted this hideous story cut from her brain. My mother was so puritanical. I was away from home at the time of the lobotomy; I would never have permitted it . . . . I would like to invite my sister Rose down to Key West for a visit."

Mr. Williams's survivors include his sister and his brother, who is an lawyer in Illinois.

In his tribute to Mr. Williams, Arthur Miller said: "He came into the theater bringing his poetry, his hardened edge of romantic adoration of the lost and the beautiful. For a while, the theater loved him, and then it went back to searching its pockets for its soul. He chose a hard life that requires the skin of an alligator and the heart of a poet."