POP MUSIC The cover on a new LP album called Sgt. Pepper's Lonely Hearts Club Band is a photomontage of a crowd gathered round a grave. And a curious crowd it is: Marilyn Monroe is there, so are Karl Marx, Edgar Allan Poe, Albert Einstein, Lawrence of Arabia, Mae West, Sonny Listen, and eight Beatles. Eight? Well, four of them, standing around looking like wax dummies, are indeed wax models of the Beatles as most people remember them: nicely brushed long hair, dark suits, faces like sassy choirboys. The other four Beatles are very much alive: thin, hippie-looking, mustachioed, bedecked in bright, bizarre uniforms. Though their expressions seem subdued, their eyes glint with a new awareness tinged with a little of the old mischief. As for the grave in the foreground: it has THE BEATLES spelled out in flowers trimmed with marijuana plants. With characteristic self-mockery, the Beatles are proclaiming that they have snuffed out their old selves to make room for the new Beatles incarnate. And there is some truth to it. Without having lost any of the genial anarchism with which they helped revolutionize the life style of young people in Britain, Europe and the U.S., they have moved on to a higher artistic plateau. Cunning Collages. Rich and secure enough to go on repeating themselves or to do nothing at allthey have exercised a compulsion for growth, change and experimentation. Messengers from beyond rock 'n' roll, they are creating the most original, expressive and musically interesting sounds being heard in pop music. They are leading an evolution in which the best of current post-rock sounds are becoming something that pop music has never been before: an art form. “Serious musicians” are listening to them and marking their work as a historic departure in the progress of musicany music. Ned Rorem, composer of some of the best of today's art songs, says: “They are colleagues of mine, speaking the same language with different accents.” In fact, he adds, the Beatles' haunting composition, She's Leaving Homeone of twelve songs in the Sgt. Pepper album”is equal to any song that Schubert ever wrote.” Conductor Leon ard Bernstein's appreciation is just as high; he cites Schumann. As Musicologist Henry Pleasants says: “The Beatles are where music is right now.” Like all good popular artists, the Beatles have a talent for distilling the moods of their time. Gilbert and Sullivan's frolics limned the pomposities of the Victorian British Empah; Cole Porter's urbanities were wonderful tonics for the hung-over '30s; Rodgers and Hammerstein's ballads reflected the sentient and seriousness of the World War II era. Today the Beatles' cunning collages piece together scraps of tension between the generations, the loneliness of the dislocated '60s, and the bitter sweets of young love in any age. At the same time, their sensitivity to the absurd is sharper than ever. Cheerful Skewering. By contrast, their early music had exuberance and an occasional oasis of unexpected harmony, but otherwise blended monotonously into the parched badlands of rock. I Want to Hold Your Hand, the Beatles' biggest hit singleit has sold 5,000,000 copies since 1963was a clich boy-girl lyric and a