EVERYONE tells the same story about him, but everyone ends it with a different twist. A portly, rather stolid man with the face of a child hovering above a powerful, stentorian chest, he would come out on stage in tails, move slowly to the center, smile once and follow that with a bow. Then it would happen.

"He opened his mouth," says film director Paul Mazursky, "and this incredible production would come out."

"He opened his mouth," says Patrick Hayes, head of the Washington performing Arts Society, "and the voice poured out like liquid silver."

"He opened his mouth," says George London, himself a worldclass baritone and director of the Washington Opera Society, "and everyone fell over."

The man with the open mouth was Jussi Bjoerling, born 70 years ago this January in a Swedish town called Stora Tuna. To say he was a dizzling singer, to say he lhad arguably the finest tenor voice of this century, Caruso's included, does not really to justice to the enormity of the man's appeal, to the quirky combination of vocal abilities and personal peculiarities which have made him, 16 years after his death, more popular than ever.

Many reasons could be given why Bjoerling shouldn't be any kind of popular at all. His acting, for instance, which kindly critics called "tame," or, in the words of his New York Times obituary, "not the subtlest the operatic stage has known," was in general considered dreadful even for a dingle.

He never did "Lohengrin," he once said, because "Who'd believe I could ever fight a battle of broadswords and win?" And the Metropolitan's General Manager Rodolph Bing nominated him as "one of the most astonishing things I ever saw on an opera stage" for the night Bjoerling, theoretically playing the hero in Puccini's "Manon Lescaut," complained of a bad back and, instead of getting water for the dying heroine as he was supposed to, had the poor woman get up and fetch it herself.

Then there was the matter of his temperament, which was at times standoffish and worse, and his list of dislikes, which was extensive. He hated rehearsals and never even vocalized in the wings before going on stage. He hated travel, he hated interviews, he even hated autographs, so much so graphs reports that signed photos of him go for upwards of $100 and are sought after more than anyone's except Caruso's.

"He could be difficult as only the extremely grifted can be," wrote Francis Robinson, the Met's longtime press and tour director. "The mere physical effort of getting him onto the stage or into town - or for that matter back to this country at all - put managers through hell."

There is more, for by all accounts Bjoerling was also a ferocious drinker who would go on terrible tears, disppearing sometimes for days at a time, missing rehearsals as well as performances.Scheduled to record Verdi's "Un Ballo in Maschera" under the baton of Toscanini, he went on a drunk, held up the production and finally was replaced by Jan Peerce when he couldn't be found. Reports claim he was capable of drinking his way down New York's Eighth Avenue, hitting every bar on both sides of the street from the mid-50s to lower Manhattan. Yet could he be found and placed on the stage, he unvariably did the job, and did it well.

Despite all his, or maybe in part because of it, opera fans do seem to be afflicted with a kind of Bjoerling madness. The afflicted include people such as Richard Asofsky, an immunologist at the National Institutes of Health, who used to stand in line for eight hours for Bjoerling tickets, went without lunches for a week when his record of "II Trovatore" came out, and even met his future wife at a Bjoerling concert.

Also devoted is director Mazursky, whose last film, the autobiographical "Next Stop Greenwich Village," featured Shelley Winters as his mother, sobbing as she listened to Bjoerling singing "Que gelida manina" from "La Boheme," an aria that Mazursky himself passionately starts to sing on the phone. "After that picture," he says, "when people came up to me, instead of saying 'That's the greatest film I've ever seen,' they said, 'Gee, I love Jussi Bjoerling.'"

Just being a collection of eccentricities would obviously not begin to account for this overwhelming popularity, for the fact that Rudolph Bing, even though he considered Bjoerling "a very irresponsible artist," still insisted on having him for the title role in the "Don Carlo" sung on the new general manager's first night at the Met. There was the matter of his voice.

It was not a particularly big voice - "It's only the slobs who have to have huge voices and scream," says James Camner - but it had wonderful, wonderful qualities. And the great charm of Bjoerling's voice is that its greatest is easily accessible that the marvelous feelings of timelessness and immortality it evokes are available just for the listening.

The voice was an oddity for opera, for Bjoerling, a singer of distinctly Scandinavian background and temperament, based his career not on the usual heavy Wagnerian roles but the fulsome romanticism of Verdi, Puccini and other Italian and French composers. The result was a gratifying sweetness and forthrightness enhancing arias which are too often heavily melodramatized. "He had a kind of emotion the Italians don't have," says Paul Mazursky. "He moved you in a way that wasn't sentimental. It wasn't a cheap shot."

The voice, both in person and on records, simply knocked people over. Charles Jahant, a Washingtonbased opera historian, uses the French word rayonnante to describe it, "a voice open and free, like rlays from the sun. It simply came out." Bjoerling himself said that when he was singing well, his voice did not seem to be in his body at all, but to float in the air about a foot in front of him. And baritone Robert Merrill, in his "Once More From The Begining," tells of sitting with Bjoerling and other opera singers at a cafe in Rome when some street singers wandered in and the opera folks decided to serenade them. Bjoerling's choice was, of all things, "O Sole Mio." Wrote Merill, "It was the most unforgettable musical experience of my life.

Jussi Bjoerling sang as I have heard no other mortal sing."

The physical outlines of Bjoerling's life were not extraordinary. The son of a tenor who also sang at the Met, he started voice lessons at age 5, toured with his father and two brothers in the Bjoerling Male Voice Quartet before he was 10, had his Metropolitan debut in 1938 and was a fixture on the international operatic scene until he died of a heart attack on Sept. 9, 1960, just six months after he'd sung "La Boheme" at London's Covent Garden - with Queen Elizabeth and the Queen Mother in the audience - despite having had a heart attack backstage.

Still, his attraction continues to grow, and though not known for his verbal quickness, it was Bjoerling himself who seemed to sum it all up best when he told fellow Scaninavian Kristen Flagstad in an inebriated moment: "They say I drink a lot, but have you ever heard a more beautiful tenor voice?"