Elvis Presley, who revolutionized American popular music with his earthy singing style and became a hero to two generations of rock 'n' roll fans, died yesterday afternoon at Baptist Memorial Hospital in Memphis, Tenn. He was 42.

Hospital vice president Maurice Elliott said Presley was discovered unconscious at his multimillion-dollar Graceland Mansion at midafternoon by his road manager, Joe Eposito, and rushed to the hospital. Initial reports attributed Presley's death to a respiratory ailment, but Presley's personal physician, Dr. George C. Nichopoulos, said that a "heart attack" also was a possible cause of death.

Capt. John McLaughlin of the Memphis Police Department denied an earlier report that detectives were investigating a possible drug overdose.

"We are not investigating the use of drugs," said McLaughlin. "I don't know where that information came from but it's not so."

Dr. Willis Madrey, specialist in liver disease at Johns Hopkins Hospital in Baltimore, said yesterday that two years ago Presley's doctors sent him a sample of Presley's liver for analyis. "It showed no significant abnormalities," Madrey said, "nothing of any help at all in evaluation.

"I had understood he was having some gastrointestinal problems his doctors were trying to evaluate," Madrey said. But "well over a year ago," Madrey added, he saw one of Presley's doctors and was told "he seemed [WORD ILLEGIBLE] and "the only problem he had medically was obesity."

At the time Madrey examined the liver issue, he said, "There was a rumor and it got on TV that Presley was coming to Johns Hopkins. He never did, but the rumor caused quite a furor. We have numbers of very famous people for patients, but the rumors that Elvis Presley might be here stirred more attention than the natual presence of most famous people."

In 1956, when Presley came crackling out of every radio speaker in the land, young Americans' notions about independence were forming, Elvis became "The King" - of rock 'n' roll, but also of the emerging youth culture. He was a young, hipthrusting white singing music that was essentially black. Part of his attraction was that the '50s teen-agers viewed him as epitomizing everything they thought their parents feared they would become - cocky, slick, brash, tough, black-leather-clad, motorcycle-straddling in stillet to shoes.

Their hunches of their parents fears were well confirmed after Presley's first appearance on a 1956 Ed Sullivan show. While millions of teenagers screamed in unison across the land, a Catholic priest in New York scored Sullivan for this "moral injury" and condemned Presley for his "voodoo of defiance and frustration."

Overall, he sold more than 250 million records and made 33 films. He was a millionaire many times over and lived in a style that reflected it: ensconed in his Graceland Mansion behind locked gates, like the reclusive character in "Citizen Kane"; handing out jewels and Cadillacs to friends and even casual acquaintances.

Born in Tupelo, Miss., on Jan. 8, 1935 - his twin brother, Jesse Garon, died at birth - Elvis Presley was 19 when he walked into a Memphis studio and paid $4 to record "My Happiness" and "That's When Your Heart-aches Begin" as a present for his mother.

Sam Phillips, owner of the studio, intrigued by the rough, soulful quality of the young truck driver's voice, invited him back to practice with some local musicians. A few months later Phillips' Sun Records released Presley's version of the blues tune "That's All Right," backed by the country song "Blue Moon of Kentucky," and the singer's career was launched.

The synthesis of black blues and white country music made Presley a unique artist from the start, and Memphis was quick to appreciate that. Presley's recording went to the top of the local charts almost immediately, eventually selling 20,000 copies, and Presley was invited to appear on the Louisiana Hayride country show and at the Grand Ole Opry.

At the Opry, however, the first of the many controversies that were to engulf Presley almost caused him to give up his career. Told by the talent booker there that he was no good, Presley broke into tears and left his performing costume in a filling station.

He recovered quickly, though, and went on to record a whole string of hits for Sun Records, which sold his contract for $40,000 - then a record - to RCA in 1955. His first record for RCA was "Heartbreak Hotel," which early in 1956 made him a nationwide sensation.

Months earlier, in November, 1955, Col. Tom Parker, an established country music agent, had concluded a management agreement with Presley. Parker was instrumental in arranging Presley's switch from Sun to RCA, and was to remain Presley's manager to the end, shrewdly guiding his client's career, limiting or encouraging public exposure in such a way that Presley was almost always able to command top dollar on the competitve concert and recording circuit.

Six months after the record "Heartbreak Hotel" had rippled heart-throbs through teenage America, Ed Sullivan promised to bring "The King" into the nation's living rooms: for $50,000 Sullivan signed Presley to three appearances.

When the first show hit the airwaves in Sept. 9, 1956, the response was predictable. Record sales soared, and the critics had new ammunition.

"It isn't enough to say that Elvis is kind to his parents," wrote jazz musician Eddie Condon. "That still isn't a free ticket to behave like a sex maniac in public before millions of impressionable kids. According to a scholarly friend of mine, Jackie Gleason, we'll survive Elvis. 'He can't last,' said Gleason. 'I tell you flatly, he can't last.'"

New York Times critic Jack Gould observed:

"Mr. Presley has no discernable singing ability. His specialty is rhythm songs which he renders in an undistinguished whine; his phrasing, if it can be called that, consists of stereotyped variations that go with a beginner's aria in a bath tub. For the ear he is an unutterable bore, not nearly so talented as Frank Sinatra back in the latter's rather hysterical days at the Paramount Theater.

"From watching Mr. Presley it is wholly evident that his skill lies in another direction. He is a rock-and-roll version of one of the most standard acts in show business: the virtuoso of the hootchy-kootchy. His one specialty is an accentuated movement of the body that heretofore has been primarily identified with the repertoire of the blonde bombshells of the burlesque runway."

Other performers on shows with Presley were puzzled by the strong reaction the young singer got from audiences. Jerry Lee Lewis took to closing his shows by standing on the piano in an attempt to upstage Elvis. But it did no good. Presley was even able to take others' material - like Carl Perkins' "Blue Suede Shoes" - and make it a hit of even greater mangitude.

"Elvis had the looks on me," Perkins once told an interviewer. "The girls were going for him for more reasons than music. Elvis was hittin' 'em with sideburns, flashy clothes and no ring on that finger. I had three kids. There was no way of keeping Elvis from being the man in that music."

A month after the first Sullivan appearance, 20th Century Fox was readying Elvis's first film for Thanksgiving release. Originally titled "The Reno Brothers," it was changed to "Love Me Tender" to capitalize on the song Presley had introduced on the Sullivan show. The studio made 575 prints of the film for its first run - the largest in Fox's history.

A year later Presley was drafted into the U.S. Army. Boarding a troop ship for an 18-month tour of duty in Europe as a jeep driver, he told a reporter: "The first place I want to go is to Paris and look up Brigitte Bardot."

As Private 533 10761, Presley was just another cog in the military machine, stationed in Frieburg, West Germany. But Col. Parker had ensured that Presley would not be forgotten during the two years he was away by having him record a stack of songs before leaving for Europe.

During his period of military service, Presley made no public appearances and completed only one recording session. Of the five singles released during Presley's absence from the U.S. rock 'n' roll scene, all eventually became million sellers. When Presley was discharged a sergeant early in 1960, he was still "The King," though stars such as Ricky Nelson had come along in the interim.

Presley returned from the Army to find that rock 'n' roll tastes had changed dramatically in his absence. Presley himself underwent a drastic change of style, eschewing his trademark sideburns and hip-shaking music in favor of romantic, dramatic ballards such as "It's Now Or Never" and "Are You Lonesome Tonight?"

These records proved to be as popular as his hard rocking numbers, but Presley by this time was more interested in making movies than anything else. After an appearance on a Frank Sinatra TV special, in which he alarmed old fans by performing in tails, Presley retired from concerts and television for nearly a decade.

His movies during this period included such potboilers as "Fun in Acapulco" and "Girls! Girls! Girl!", disillusioning some fans even further. But in 1968, Col. Parker engineered a change of direction, and Elvis, who had seemed to many to be old-fashioned after the emergence of the Beatles in 1964, once again became the hottest thing in pop music.

The vehicle of Presley's comeback was a Christmastime TV special, broadcast by NBC. The response to that show encouraged Presley to get together with guitarist James Burton and pianist Glen D. Hardin, two of rock's top recording session musicians, and go out on the road again.

His audience on that concert tour - and on subsequent tours, which brought him to the Washington area three times in recent years - was more mature than that of a decade earlier, reflecting perhaps the fact that Presley himself was settling down.

On May 1, 1967, Presley had married Priscilla Beaulieu, the daughter of a U.S. Army colonel. On Feb. 1, 1963, a daughter, Lisa Marie, was born to the couple. The marriage ended, after lengthy and expensive divorce proceedings, in October, 1973.

Reports of Presley's declining health and increasing weight first date from this time. By 1976, in the authoritative "Rolling Stone illustrated History of Rock 'n' Roll," critic Peter Guralnick was moved to say:

"It seems to be a continuing battle against mortality, and Elvis is not winning. His hair is dyed, his teeth are capped, his middle is girdled, his voice is a husk, and his eyes film over with glassy impersonality. He is no longer, it seems, used to the air and, because he cannot endure the scorn of strangers, will not go out if his hair isn't right, if his weight - which fluctuates wildly - is not down. He has tantrums onstage and, like some aging politician, is reduced to the ranks of the grotesque."

Earlier this year, Presley canceled several performances in Louisiana and returned to Memphis for what his physicians said was exhaustion. And in Baltimore, he cut short a show and disappeared from the stage for several minutes, only to return claiming he had merely been answering "the call of nature."