It's odd, unseemly even, to realize that Marlon Brando is nearly 80 years old. The bubble of enigma that has surrounded the actor since Dec. 3, 1947 -- when he stepped on stage as Stanley Kowalski in ''A Streetcar Named Desire'' and set off a thermonuclear reaction that expanded far beyond Broadway -- has blurred the specifics of his life and personality. When we say ''Brando,'' we mean both the blinding arc of his early talent and the capricious bloat that followed. We mean genius and waste, charisma and entropy, Terry Malloy and Colonel Kurtz. ''Brando'' -- it's impossible to invoke him without shaking your head in wonder and dismay.
Can anyone connect the dots of this life? Well, yes: the man who lived it. And in fact the actor does pin down the twin poles of his own mystery toward the very end of Patricia Bosworth's Marlon Brando, a new entry in Penguin Lives, a popular series of short biographies, now numbering more than 18, in which well-known writers take on subjects ranging from Leonardo da Vinci to Andy Warhol. Bosworth quotes a recent ex-girlfriend of Brando's who, while watching TV with him, channel-surfed upon ''Streetcar.'' ''Marlon told me, 'Turn it off,' but I'd never seen it, so I said, 'Please, lemme watch.' So we did for a while, and then Marlon groaned, 'Oh God, I was beautiful then. But I'm much nicer now.'''
The effect, coming after 217 pages of clean, unbiased, scrupulous reportage, is like watching Rosebud tossed to the flames. Connections crackle in the reader's head; the grain of the wood suddenly shows. The story of Brando's career is that of rage intensely focused and gradually dispersing, and of a man too involved with those feelings to care much about art, craft, or, God forbid, an audience. This only seals his status as proto-boomer template: Brando prefigured a generation's discontent -- and its self-absorption.
There are plenty of biographies out there, with Peter Manso's 1,118-page 1994 behemoth the acknowledged, if controversial, benchmark. As with other titles in the Penguin Lives series, ''Marlon Brando'' is an attempt to cut through the noise with concision and brevity. ''Brando for Dummies'' this is not; rather, Bosworth's just-the-facts clarity is a tonic for the stressed, literate reader whose beach bag can't stand the weight of one more doorstop bio of a founding father.
The focus, as it should be, is on the actor's early glory, cresting almost exactly halfway through the book with ''On the Waterfront,'' ''the peak of Brando's career.'' He had fled a distant, abusive father and a beloved, alcoholic wreck of a mother to surface in New York, where he halfheartedly pursued acting and mesmerized his small circle of friends, then the Broadway community, then the world. Bosworth, the author of previous works on Diane Arbus and Montgomery Clift, has done her research, and ''Marlon Brando'' navigates eloquently between the actor's stage and screen work and the rumpled prankishness of his private life. She charts Brando's complicated relationship with director Elia Kazan, his adoration of childhood pal Wally Cox, his indulgence of his pet raccoon, Russell. And she hints that, with the exceptions of ''The Godfather'' and ''Last Tango in Paris'' -- one a brilliant submersion in character, the other a frightening blurt of self-expression -- Brando simply lost interest in the game after his mother's death in 1954.
Bosworth's style of pruning away until the true lay of the land becomes clear is the great strength of ''Marlon Brando'' -- and, ultimately, a source of disappointment. Bosworth is a hell of a writer, and she's just about the only biographer to refrain from judging him (that he hasn't lived up to our expectations, she suggests, isn't his problem). Yet you can feel her insights knocking against the walls of journalistic objectivity, and her book might have been better if she had let some of them in.
Other Penguin Lives have balanced fact and analysis: Karen Armstrong's ''Buddha,'' for instance, deftly places scanty biographical data into the historical long view, while Elizabeth Hardwick's ''Herman Melville'' positively broods on the notion of the writer as 19th-century misfit. Marlon Brando certainly belongs on this shelf: Despite latter-day disinterest and self-parody, he transformed acting as surely as Beethoven changed music and Picasso revolutionized painting. That Bosworth only fitfully examines why is all that keeps her from becoming his Boswell.