Steve McQueen, who transcended a delinquent, restless youth to parlay an appealing, low-key presence and extraordinary eye-contact into international popularity as a star of Hollywood, action and adventure movies, died yesterday in a hospital in Jarez, Mexico. He was 50.

His death was caused by a heart attack that occured several hours after he had undergone surgery for the removal of a cancerous neck tumor.

This summer, Mr. McQueen ended years of rumor and speculation about his health by acknowledging that he had mesothelioma a form of lung cancer usually considered incurable. The disease had spread to his stomach, chest and neck.

"The reason I denied I had cancer," he revealed, "was to save my family and friends from personal hurt and to retain my sense of dignity . . . Hopefully, the cheap scandal sheets and curiousity seekersill will not try to seek me out so I can continue my treatment. I say to all my fans and friends, keep your fingers crossed and keep the good thoughts coming." f

The wary, unassuming note of heroic fortitude evident in Mr. McQueen's statement about his illness corresponds to the film image that made him such a popular screen personality. This image began in a significant way with his costarring in "The Magnificient Seven" in 1959, and continued for 15 years through hit vehicles such as "The Great Escape," Love With the Proper Stranger," "The Cincinnati Kid," "Nevada Smith," "The Thomas Crown Affair," "Bullitt," "The Reivers," "Papillon," "The Getaway" and "The Towering Inferno."

Adroit as both a reticent yet supremely self-confident man of action and a diffident yet devilishly attractive romantic lead, Mr. McQueen perfected a disarmingly enjoyable, contemporary illusion of masculine self-assurance. His most impressive embodiments of the man of action were probably his roles as the cocky American prisoner-of-war in "The Great Escape" and the cagy San Francisco police detective in "Bullitt." His equally astute romantic flair found its classiest expression in the role of a scheming, sexy criminal mastermind in "The Thomas Crown Affair."

But whether he was playing a man of action or a man of affairs, Mr. McQueen had an elusive ability to convey to his audiences the sense that he was playing someone who mattered -- or at least someone who was entirely credible in terms of the film. He was, in short, an actor.

Mr. McQueen's concern about his health no doubt accounts for mystifying aspects of his career over the past few years, notably an unsuccessful attempt to convince the producers of "A Bridge Too Far" and "Apocalypse Now" to pay him $3 million for three weeks of work on each production.

As his illness worsened and he became resigned to the likelihood of death, Mr. McQueen declined conventional medical advice and entered a clinic, the Plaza Santa Maria Hospital near Tijuana, Mexico, for an experimental, controversial course of treatment, administered by Dr. Rodrigo Rodriguez, director of the hospital, and Dr. William D. Kelley, a former Dallas dentist.

The therapy reportedly included intramuscular injections of animal cells, massive doses of vitamins, an organic diet, coffee enemas and laetrile. Mr. McQueen had remained in seclusion during his confinement. However, Dr. Kelley and his associates reported on the patient's progress at several news conferences and indicated that the growth of the cancerous tumors had been arrested.

Mr. McQueen had been released from the Plaza Santa Maria Hospital for a brief vacation at his ranch near Santa Paula, Calif. Last Sunday, his doctors announced that he would probably undergo surgery this week for what was characterized as a "dead" tumor on his neck. He underwent the operation in Juarez.

According to publicist Warren Cowan, Mr. McQueen died at 2 a.m. Friday, attended by his third wife, former model Barbara Minty, and his daughter and his son by his first wife, the former dancer-actress Neile Adams -- Terri, 21, and Chad, 19. Mr. McQueen and Miss Adams were married in 1956, when both were promising newcomers on Broadway, and divorced 15 years later. Mr. McQueen's 1973 marriage to actress Ali MacGraw ended in divorce in 1978. He and Miss Minty were married last January.

Mr. McQueen was born Terrence Stephen McQueen on March 24, 1930, in Beech Grove, Ind., near Indianapolis. His father dropped out of sight during Mr. McQueen's infancy. Some sources say that he abandoned the family and others that he died. Mr. McQueen's mother left her child with her parents, a farm couple living in Slater, Mo., and moved to Los Angeles, where she eventually remarried.

At the age of 14, Mr. McQueen joined his mother and stepfather in Los Angeles. It was a happy reunion. The boy was soon running with a delinquent crowd and getting into minor scrapes with the law. As he recalled during the shooting of "The Great Escape," "If they were making a movie of my life, they could call it 'The Great Escape.' I could just as easily have wound up a hood as an actor. I was pretty hard to handle as a kid. My mother sent me to Boys Republic, a school in Chino, Calif, for problem kids. It's probably the best thing that ever happened to me: they straightened me out there."

Despite this testimonial, Mr. McQueen evidently sustained a prodigal youth after dropping out of Boys Republic in the ninth grade. He signed on as a deckhand on a Greek tanker sailing for South America, jumped ship in the Dominican Republic and worked his way back to the United States, where he embarked on a colorfully itinerant career as a lumberjack, roughneck, carnival huckster, traveling salesman, delivery boy, television repairman, bookie's runner and bartender, among other trades.

Mr. McQueen enlisted in the Marine Corps in 1948 and eventually served as a tank driver and mechanic. He also did six weeks in the brig on one occasion for stretching a weekend pass into a two-week furlough.

Discharged (honorably) in 1950, he made his way to Greenwich Village and luckily stumbled onto his true profession. An actress friend introduced him to Sanford Meisner, director of the Neighborhood Playhouse.

Meisner cast the startled novice in a bit role in a Yiddish play and then took him as a drama student. Mr. McQueen continued his studies with Uta Hagen and Herbert Berghof and then at the Actors' Studio. He appeared in summer stock productions of "Peg O' My Heart" with Margaret O'Brien and "The Member of the Wedding" with Ethel Waters. He toured in the national company of "Time Out for Ginger" with Melvin Douglas.

Mr. McQueen made his Broadway debut in 1956 with a role in "The Gep." Later that year, he won his first leading role, replacing Ben Gazzara in "A Hatful of Rain" and attracting favorable notice. During this period, he also acted frequently in New York based television shows and made his feature film debut as a bit player in "Somebody Up There Likes Me," directed by Robert Wise.

A decade later, Mr. McQueen won his only Academy Award nomination for his starring role in "The Sand Pebbles," also directed by Wise. Mr. McQueen and the star of "Somebody Up There Likes Me," Paul Newman, were destined to costar in "The Towering Inferno" many years later. nThey also came to share a notable enthusiasm for auto racing.

Mr. McQueen and his new bride, Neile Adams, went to Hollywood with high career hopes in 1957. A role as a laconic, steely-eyed bounty hunter in the television Western series "Trackdown," which starred Robert Culp, proved so striking that it secured Mr. McQueen a spin-off series of his own. pFor three years he played bounty hunter Josh Randall in a series called "Wanted -- Dead or Alive."

Mr. McQueen played leads in two minor features. "The Blob" and "The Great St. Louis Bank Robbery," and supporting roles in two others, "Never Love a Stranger" and "Never So Few," before landing his made-to-order assignment as the droll, expert second-in-command of "The Magnificent Seven," the rousing Western remake of Kurosawa's "Seven Samurai" that also had a lot to do with the careers of Charles Bronson, James Coburn and Robert Vaughn.

His decisive career break came in "The Great Escape." His climactic stunt sequence on a motorcycle, particularly the moment when he vaulted an eight-foot fence on his bike, turned him into an international action favorite. Mr. McQueen performed the stunt himself, and in its way it was as thrilling as the trickiest routine ever finessed by Fred Astaire and Gene Kelly.

In 1969 and 1970, Mr. McQueen was rated the third most popular box office star in the United States by Motion Picture Daily.

It is conceivable that his troubled youth helped imprint on his work that watchful quality that was peculiarly fascinating on the screen. There always seemed to be some interesting calculation going on behind his eyes, which revealed a cunning affinity for the camera lens right from the start. "Bullitt" became a sensation because of its thrilling car chase sequences, but the disheveled threads of the plot were neutralized by Mr. McQueen's eyes. It was a classic example of how a star presence can hold a movie together.

Of course, there were two schools of thought about Mr. McQueen's guarded style. Some critics complained that he never did anything. Admirers responded that the apparent lack of effort was the whole point: Mr. McQueen had achieved the kind of sheer physical eloquence that suggests volumes about the drives and thought processess of a character.

One of the admirers, film historian David Shipman, argued that "Steve McQueen can act with the back of his head. He can act without doing anything. . . . His voice isn't remarkable and he shows no sign of versatility. But versatility, where he is concerned, is immaterial. He has only to appear on the screen to fill it."

Mr. McQueen once evaluated himself with a typical, becoming modesty. "I'm not a great actor," he said, "let's face it. I don't have a great deal of scope. Someone like Richard Burton has great range as an actor. There are certain things I can do, but when I'm bad, I stink. . . . There's something about my shaggy-dog eyes that make people think I'm good. I'm not all that good."