Isaac Asimov, 72, an imaginative and gifted storyteller and one of this century's most versatile, prolific and celebrated writers of science fiction and fact, died of heart and kidney ailments April 6 at New York University Hospital.

Mr. Asimov was author of more than 320 books, plus scores of short stories and nonfiction articles published in journals and magazines, and his total literary output is said to have been more than 20 million words in print.

A biochemist by training, he was a master at translating complicated scientific facts and principles into simple everyday prose. His work included not only science fiction stories of mystery and adventure, but also medical texts; science books for the general public on topics ranging from the nature of carbon to the genetic code; astronomy; mathematics; humor and satire; literary studies; and books about Greek, Roman and biblical history.

He could type 90 words a minute, and he revised his writing only once. "If after two typings the result proves unsatisfactory, it has always seemed to me it is better abandoned," he wrote in his autobiography. "There is less trouble and trauma involved in writing a new piece than in trying to salvage an unsatisfactory one." He once said that for him writing was a pleasure, and he generally wrote for about 12 hours a day, stopping only for meals and an occasional coffee break. He rarely took vacations and said he never experienced the writer's block that plagues so many authors.

By his own estimate, Mr. Asimov was best known as the formulator of the "Three Laws of Robotics," which he said became the basis of more than two dozen short stories and several novels. He coined the term "robotics," he said, and its three basic laws were:

A robot may not injure a human being or, through inaction, allow a human being to come to harm.

A robot must obey the orders given it by a human being except where such orders would conflict with the First Law.

A robot must protect its own existence as long as such protection does not conflict with the First or Second Laws.

Mr. Asimov's robot books included the novels "I, Robot," published in 1950, "The Caves of Steel" (1954) and "The Naked Sun" (1957). The first of these was set in the year 2058, and it was a science fiction thriller told from the perspective of a robot psychologist, Susan Calvin. The latter two were science fiction detective stories featuring the law enforcement team of Elijah Baley, a human, and R. Dancel Olivaw, a robot. Baley and Olivaw reappeared in later stories.

In 1966, Mr. Asimov won science fiction's highest prize, the Hugo Award, for his "Foundation" series, a collection of short stories published in magazine form in the 1940s, then combined into a trilogy, "Foundation," "Second Foundation" and "Foundation and Empire," in the early 1950s. These novels were said to have been inspired by Edward Gibbon's "Decline and Fall of the Roman Empire," and they were written as a "future history" about a society in the distant future in which the planet Earth has been forgotten and men and women are governed by an empire that has lasted 12,000 years. As his career progressed, Mr. Asimov returned time and again to his works of future history, and the series came to include themes from robot stories. A final novel, "Forward the Foundation," was finished only months ago and will be published this year.

Mr. Asimov also was widely known for the short story "Nightfall," which is the single most popular piece he ever wrote. Published in 1941, the story finished first in a poll of all-time science fiction favorites 30 years later by the Science Fiction Writers of America. It was based on a quotation from Ralph Waldo Emerson, "If the stars should appear one night in a thousand years, how would men believe and adore; and preserve for many generations the remembrance of the city of God." John W. Campbell, one of Mr. Asimov's editors early in his career, suggested to the author that he write a story about how men would react to the stars if they were visible only once every thousand years. "Nightfall" is the story of a civilization on a planet visited by darkness only once every 2,000 years. When nightfall occurs, the social system collapses. Campbell paid Mr. Asimov $150 for the story.

Mr. Asimov was born in the Russian village of Petrovichi, about 250 miles southwest of Moscow. The family immigrated to the United States in 1923 and settled in Brooklyn, where Mr. Asimov's parents opened a candy store. It was there that the future author first became interested in science fiction, reading stories from publications in the store's magazine rack.

He started writing science fiction while a student at Columbia University, from which he graduated and received master's and doctoral degrees in chemistry. During World War II, he worked as a chemist at the Naval Air Experimental Station in Philadelphia, then served in the Army.

After the war, he did postgraduate study on nucleic acids at Columbia, then in 1949 accepted an invitation to join the medical school faculty at Boston University. In 1950, while teaching at Boston University, he wrote his first science fiction novel, "Pebble in the Sky," a story about a man who is transported by a nuclear accident from the 20th century to the Galactic Era 827.

With two colleagues at the medical school, Mr. Asimov wrote a medical textbook, "Biochemistry and Human Metabolism," which was published in 1952. "That introduced me to the delights of nonfiction," he said later. "I went on to discover the even greater ecstasies of writing science for the general public."

During his years at Boston University, Mr. Asimov's classroom and laboratory duties forced him to restrict his writing to weekends. In 1958, he left teaching to write full time. His 100th book was published in 1969 and his 200th a decade later.

In 1966, he wrote "Fantastic Voyage," a popular story about a miniaturized medical team's being injected into the bloodstream of a defecting Soviet scientist. The book later became a movie starring Raquel Welch.

He also wrote a series of juvenile science fiction novels about an astronaut named Lucky Starr, and he wrote a collection of humor and satire pieces under the name of Dr. A. These, including "The Sensuous Dirty Old Man" (1971), "Lecherous Limericks" (1976) and "Limericks: Too Gross" (1978).

Asked once by ABC Television's Barbara Walters what he'd do if he had only six months to live, Mr. Asimov answered, "I'd type faster."

His marriage to the former Gertrude Blugerman ended in divorce.

Survivors include his wife, retired psychiatrist Janet Jeppson, of New York; two children from his first marriage, David and Robyn; a sister, Marcia Rapanes; and a brother, Stanley Asimov.