MARIO LANZA died in Rome in 1959 at the age of 38. His movie career, spanning about 10 years, consisted of only seven films. Yet he seems to have had a strong influence on major figures in the music world. On a television special last year, Luciano Pavarotti cited Lanza as a major inspiration in his career. And tonight at 9 on Channel 13, a documentary titled ''Mario Lanza: The American Caruso'' has as its host Placido Domingo, who insists that the Lanza name has signified ''magic for two generations.''
The story of Mario Lanza, christened Alfred Cocozza at his birth in Philadelphia, is finally a story of what might have been. In the mid-1940's, he toured the country as part of the Bel Canto Trio, which included Frances Yeend and George London. It wasn't long, though, before he settled in Hollywood, where Joe Pasternak, the producer, took the kinks out of his hair and made him lose 25 pounds for the picture ''That Midnight Kiss.'' Lanza was packaged as the singing truck driver from Philadelphia, but as this first-rate Camera Three Production points out, he never did any manual work. His mother was the one who worked to pay for his singing lessons.
His career reached a peak with ''The Great Caruso,'' but he was always hounded by problems. In one movie, his weight fluctuated by 80 pounds, turning the character into almost two completely different people. He drank too much, and he liked women too much. He was temperamental on the set and did not have pleasant relations with the press. He was eventually on the verge of a nervous breakdown and then decided to move to Italy.
Mr. Domingo offers the most familiar theory associated with all this misery. The movie star was the victim of a failed dream; he ''never got what he wanted - the stage of an opera house.'' The movies, it seemed, had once again destroyed a great artist. But, in fact, there is little evidence that Mario Lanza wanted a stage career. His movie singing was recorded. Once booked into a Las Vegas nightclub, he failed to show up. And even on a television special that was supposed to be live, he was discovered to be lip-synching to an old recording.
He remains a minor figure, almost a curiosity, in the world of music. He never became the American Caruso. Yet his story is fascinating.