Rudolf Nureyev, 54, a charismatic and mercurial superstar of dance whose technical virtuosity and passionate intensity transformed ballet dancing in the 31 years since his dramatic defection from the Soviet Union, died yesterday in Paris.

His physician, Michel Canesi, said he died of "a cardiac complication, following a cruel illness," but declined to elaborate or give the place of death. His physical condition had deteriorated visibly and dramatically in recent years. Within the professional dance community, there were widespread rumors -- never confirmed -- that Nureyev suffered from AIDS.

Regarded as one of the premier dancers of the century, Nureyev was a magnetic performer who was credited with redefining the role of the male dancer while conquering vast new audiences for ballet throughout the western world.

A cultural icon whose complex personality seemed founded on contradiction -- charming and rude, good-humored and sullen, innocent and crafty -- Nureyev appeared to be an embodiment of the tempestuous image of the true romantic, rootless and alone, willing to place art above all.

At the same time, reviewers found that part of the fascination of his performances, which made him an enduring attraction for three decades, was the tension between the expression of his seething passion and the cool, controlled display of craftsmanship, technique and athletic prowess.

One of the great periods of his career was the time of his partnership with Dame Margot Fonteyn in London's Royal Ballet. Nureyev was credited with raising his more seasoned partner to new levels of excellence.

People who knew nothing of the ballet were drawn to their performances; tickets were bid up to the hundreds of dollars; young women flocked around his automobile chanting "Rudi, Rudi."

Nureyev was born March 17, 1938, on a train. It was crossing Siberia, on its way to Vladivostok, where his soldier father was then stationed.

His parents were Tatars. "I am Tatar," he would tell interviewers later, "not Russian." Nureyev's childhood, which was spent in Ufa, included the grim years of World War II and left him with memories of a potato diet and a room shared with nine others.

In school, he was described as a behavior problem, a loner who jumped about the schoolroom like a frog.

After learning folk dances at school, he entertained wounded soldiers. When he was 8 years old, he saw a ballet; three years later he managed to get lessons.

He got parts as a teenager at the opera in Ufa. Leaving school at 15, he taught folk dancing and attended ballet classes, becoming a member of the corps de ballet at 16.

The next year, he won a place in the Leningrad Ballet School, where he studied under the celebrated teacher Alexander Pushkin. By winning a national contest, he earned a place in the Kirov ballet.

He toured the provinces, danced at youth festivals in Vienna and Berlin, and once performed for Nikita S. Khrushchev at a villa outside Moscow.

Chosen in 1961 to be the Kirov's leading dancer for a tour of France and England, Nureyev at age 23 made a hit with western critics.

His refusal to join the Communist Youth League was only one way he irritated his company's chiefs. He chafed at what he saw as the rigid organizational lines that kept him from dancing as often as he believed he deserved to.

On June 17, after finishing its stay in Paris, the troupe was at Le Bourget airport, headed for London. Nureyev's sins had earned him a return to Moscow.

Nureyev, according to one account, drifted slowly through the waiting room. Then, he jumped into the midst of a sea of travelers.

A security man guarding the troupe was hard on Nureyev's heels. The security man grabbed him and they wrestled. "I won't go!" Nureyev shouted. He darted through the crowd, jumped a railing, threw his arms around two bewildered French police officers. "I want to stay," he cried.

As Nureyev observed a few years later, in English that was still being improved, the decision to defect was necessary but not totally satisfactory. "I know then," he told an interviewer, "that I never go back to my own country and that I never be happy in yours."

In the West, Nureyev lived to a large extent by his own rules, displaying a head of shaggy locks before long hair was fashionable.

The often petulant Nureyev could suddenly confront a photographer and order: "Vanish!" But he could compromise when necessary, slowly learning to say good morning, please and thank you.

He learned to savor the material delights of the West, starting with a furnished room, then acquiring lavish apartments and a luxurious villa. The stares of an admiring public were not always welcome, but he could accept them.

"Show people," he explained, "are sacrifice people."

He danced with the ballet of the Marquis de Cuevas in the year of his defection, and his American debut came with Maria Tallchief on the Bell Telephone Hour.

In 1962 he made his London debut with Fonteyn and the Royal Ballet in "Giselle."

He made guest appearances with at least 25 companies from Denmark to Australia; choreographed such classics as "Romeo and Juliet" and "The Nutcracker"; and made several films, including "Romeo and Juliet" and "Swan Lake."

In 1983, he became artistic director of the Paris Opera Ballet. Six years later, he became the company's principal choreographer. Last summer he made his U.S. debut as a conductor in New York with American Ballet Theater.

Nureyev made his final appearance on the stage on Oct. 8 at the Paris premiere of "La Bayadere," for which he had provided new choreography. Looking gaunt and requiring help to walk, he blinked back tears as the audience gave him a 10-minute ovation.