ANY MEASURE of the Beatles' phenomenal and lasting success as musicians, artists and -- even, in a way -- social commentators leans on the complex contributions of John Lennon, whose life ended at 40 in a hail of bullets from the handgun of a madman on the sidewalks of New York.

The shock of John Lennon's death is worldwide and twofold: First, that America continues insanely to live and die by the handgun daily has been telegraphed dramatically around the world with yet another assassination of a celebrity. Second, that a point man in a musical revolution-turned-legend has been killed is a blow to a generation that he helped to shape. As the eloquent commentaries in today's Letters to the Editor columns reveal, both the loss of John Lennon and the manner in which it occurred are difficult to accept.

Almost as unlikely were the beginnings of this Cinderella story in the slums of Liverpool in the early 1960s. Four impish young Britons were setting their country on its musical ear with a new sound -- a rock with sophisticated harmonies, and a spectacular performance to go with it. With high-powered hype and long (it then seemed) hair, the quartet went on to capture the affections and allowances of America's young in 1964, with "I Want To Hold Your Hand," with the movie "Hard Day's Night" and with appearances that packed any place they invaded. The albums sold by the millions, the music grew from new to better and then on to acceptance by the full range of composers and entertainers.

The private life and times of John Lennon were more difficult to appreciate, and more subject to extremes of criticism and adoration; perhaps too much was and will be made of his often mystifying political statements on people and events. Far more difficult to overstate -- and far more pleasant to recall -- is the rich and permanent legacy of musical artistry that will fill the air for grateful generations.