Hollywood can manufacture leading men from a certain mold: tall and rugged-looking, with even features and pleasing voices. People usually tire of them after a few movies. What it cannot manufacture is a James Cagney. He was short and not especially handsome, but when he was on screen it was, as Will Rogers once observed, "like a bunch of firecrackers going off all at once."

No one quite understands how that sort of explosiveness is generated. In the case of Mr. Cagney it seems to have come from growing up poor in a New York neighborhood where you had to do a lot of fighting. Many of his contemporaries graduated to prison, and one went to the electric chair. Mr. Cagney got into acting. His first big movie role was in "The Public Enemy" as a tough guy, a type for which he went on to set the standard. He played it in a succession of movies that were often low-budget and would probably, most of them, have been terrible without him.

But long before a generation of impressionists had started mining the Cagney tough-guy vein (was there ever a TV variety show in the 1950s that didn't include one of them snarling, "You dirty rat") and until his rather premature retirement in 1961, Mr. Cagney proved himself in a wide variety of roles, from Bottom the Weaver in "Midsummer Night's Dream" to Adm. William F. Halsey in "The Gallant Hours." His distinctive and intense manner made him one of those rare actors whose presence -- the sound of his voice, his gestures -- is invoked by the mere mention of his name. It was probably this quality that made the impressionists think they could "do Cagney," but none ever quite got him right; he was always better than they.

Mr. Cagney was still much in demand when he retired after a 30-year movie career, but he had other things he was interested in, among them writing, music and painting. The only one of his movies he liked to watch was "Yankee Doodle Dandy," made in 1942. That film, the story of songwriter George M. Cohan, is shamelessly corny, sentimental and patriotic. Without Mr. Cagney it might have turned out like so many of those wartime curiosities in which a singing cast of hundreds cascades across the movie studio's idea of a battleship deck. Mr. Cagney, however, sang, danced and acted it into a minor classic. It's always on some channel around the Fourth of July, and many of us have probably watched it more times than its star did. It is part of Mr. Cagney's unique legacy.