Roland Barthes, 64, a French literary and social critic whose studies of language and contemporary mythology have been widely influential, died Wednesday at the Pitie-Salpetriere Hospital in Paris.

He suffered severe chest injuries Feb. 25 when he was struck by a car on a Paris street, and had been on a respirator in the hospital's intensive care unit since them.

The author of almost a score of books and dozens of essays, Mr. Barthes was regarded as the heir apparent to Jean-Paul Sartre's mantle as France's preeminent intellectual. American critic Susan Sontag called him "the most consistently intelligent" as well as "the most important and useful critic -- stretching that term -- to have emerged anywhere" in the past 25 years.

An abstruse and sometimes oracular writer, Mr. Barthes was an exponent of semiology, which is the study of signs in all their manifestations, including music and language. Through the application of semiology and linguistics, he undertook to analyze the structure not only of literature, but also of "ritual convention (and) public entertainment."

If Mr. Barthes' methods were the rarified ones of the high critic, the continuing preoccupation of his life was the relatively common one of bourgeois "mythology." He argued that it is through an always-developing body of "myths" that the middle class imposes its system of values on society as a whole.

And it is the pernicious genius of the middle class, mr. Barthes wrote, to present its values -- a "rhetoric of retaliation" based on "bookkeeping" -- as products of nature itself. As products of nature, they are regarded as the only possible system of values rather than the outgrowth of an historical process that generates a choice of values. To the extent that the members of society remain unaware of values other than those dictated by the middle class, they are diminished as humans, in Mr. Barthes' view.

In "Mythologies," which was published in France in 1957 and in this country in 1972, Mr. Barthes said that a myth has "the task of giving an historical intention a natural justification, and making contingency appear eternal. Now this process is exactly that of bourgeois ideology."

Mr. Barthes developed his ideas through the examination of particular examples. His interests ranged from "the face of Garbo" and "the brain of Einstein" to the place of steak and French fries in the hearts of Frenchmen and "the world of wrestling."

He also examined himself in an autobiography, "Roland Barthes," published in 1978, and in "A Lover's Discourse," which came out the same year.

He concluded the first book with a question and an answer: "And afterward? What to write now? Can you still write anything? One writes with one's desire, and I am not through desiring."

In "A Lover's Discourse," he wrote that his investigation of love and desire "has been restored to its fundamental person, the I, in order to stage an utterance, not an analysis."

Mr. Barthes was born at Cherbourg, France, on Nov. 12, 1915. His father, a naval officer, was killed in World War I. His mother, Henriette Binger Barthes, raised the young Roland and his brother on the income she made as a bookbinder. The family lived in Bayonne and later in Paris.

Mr. Barthes was a brilliant student. His progress toward the highest academic circles was interrupted, however, when he was 18. He developed pulmonary tuberculosis, an illness that required periodic hospitalization until the late 1940s. Thus he was unable to take the competitive examination for admission to the Ecole Superieure Normale, normally a prerequisite for a university position.

But he read French, Latin and Greek at the University of Paris. He was exempted from military service because of his health during World War II and spent those years teaching or as a patient in various hospitals and sanitariums.Later he taught in the French Institute in Bucharest, Romania, and at the University of Alexandria, Egypt.

His first important book, "Writing Degree Zero," was published in France in 1953 and in English in 1967. Although "Mythologies" is now considered one of his most influential books, Mr. Barthes did not become a household name in France until 1964, when he published "On Racine."

He described Jean Baptiste Racine, one of France's greatest dramatists, as "the empty center around which his plays can be read" and argued that the essence of the plays was "the use of force within a situation that is generally erotic." This provoked a long-running litterary battle with the critic Raymond Picard, who accused Mr. Barthes of "dogmatic impressionism" and other crimes against French literature.

Other books by Mr. Barthes include "S/Z," a minute dissection of a short story by Balzac in which he purports to find five "codes," or levels of meaning. Many scholars regard it as an essential work to the understanding of fiction.

In a review in "Newsweek" on "A Lover's Discourse," Douglas Davis summarize the direction in which Mr. Barthes' thinking was going at that time. It could, perhaps, be an epitaph.

"Whereas he was once the aloof prophet of semiology . . . he is now the new voice of warmth, of sentiment," Davis wrote. "The shift is not likely to help him preserve his cherished isolation."