Who was Frankie La Porte? : A new biography claims Al Capone shared power with an even tougher, but publicity-shy, gangster : CAPONE: The Man and the Era, <i> By Laurence Bergreen (Simon & Schuster: $30; 720 pp.)</i>

The myths about Al Capone feed off each other--and the hunger never seems to be satiated. Here’s another biography, “Capone: The Man and the Era.” In this case Laurence Bergreen’s fervent approach may have cut away much of the fatted legend.

There’s an impressive lot of solid scholarship (i.e., reporting) in this big biography, with the result that Bergreen’s might well be the most accurate Capone in all the library full of the man and that raucous era.

Bergreen also lays in a giant conundrum: one Frankie La Porte, whom he describes as “the least-known, most influential racketeer of his day.” He quotes one old-time newspaperman relating that Capone would cower in La Porte’s intimidating presence, as if Capone were working for him, not the other way around, and that La Porte shared command with Capone.

“No one would ever make a movie about Frankie La Porte,” Bergreen writes, “for he avoided publicity with the zeal that Al Capone had once displayed in seeking it, but he remained the most powerful and capable racketeer of them all.”

But who was La Porte? The above is just about all Bergreen gives the hapless reader, who is now intrigued to the teeth about this mighty mystery man.

As for Big Al, there’s no shortage of caricatures. Take your pick: He was (a) an extra swell guy and a pal forever, (b) a generous, loving family man, (c) a wily gangster-entrepreneur in silk underwear, (d) a loudly dressed thug and murderous fiend in a felt fedora, (e) a poor, put-upon, misunderstood public benefactor who just gave people what they wanted, a few harmless vices, or (f) all of the above.

Capone is pretty well acknowledged to have been everything above, and Bergreen (“James Agee: A Life” and “As Thousands Cheer: The Life of Irving Berlin”) puts them all together in a sprightly mosaic. He tempers his portrait with a carefully built case asserting that Al’s latent syphilis led to his craziest, most erratic behavior.

Capone most probably contracted the disease in his very young years from a neighborhood prostitute, and then the symptoms seemed to go away. It’s recognized that syphilis led to his Alzheimer’s-like dementia in later years and his eventual death in 1947 at age 48.

But Bergreen’s claim is that Capone’s megalomania, occasional hallucinations and penchant for brutality were the result of tertiary syphilis, and that, without the disease, there never would have been a larger-than-life Al Capone.

Bergreen also boldly builds a case that Capone ingested cocaine on a regular basis and this, too, augmented his often bizarre behavior. Some authorities would assert that the Chicago mob was notoriously opposed to drug use, but then others counter-assert that cocaine wasn’t considered dangerous in those days.

The author fleshes out his characterizations with zealous pursuit of anybody still around who knew anything--old caddies, for example. Funny testimony comes from Timothy Sullivan, who was 12 in 1925 when he was a caddy at Burnham Wood for a motley foursome of “Scarface Al,” mob bookkeeper Jake “Greasy Thumb” Guzik, Jack “Machine Gun” McGurn and Fred “Killer” Burke. (The latter two assuredly were shooters at the later St. Valentine’s Day Massacre.)

They all may have had impressive nicknames, but their drunken performances on the links were less than impressive. Capone seemed gentle and patient to young Tim but his golf, well, “I don’t think he broke 60 for the nine holes,” Sullivan relates. “He could drive the ball half a mile but he always hooked it and he couldn’t putt for beans.”

Sullivan computed that at $500 per hole (big money these days, much bigger those days), the gangsters exchanged about $10,000 that game. Being gangsters, of course, they cheated each other, and the boy carried extra balls in his pocket, dropping them as needed for better lies and nice tips from Al.

Capone naturally had a .45 revolver hidden in his golf bag and, just as naturally, one day the gun went off and the bullet hit him in the groin. His golf partner, Mayor Johnny Patton, ran him to St. Margaret’s Hospital in Hammond. Sullivan relates that thereafter “the boys” always checked their safety catches as they set out on the course.

Besides the Frankie La Porta mystery, Bergreen delivers some intriguing elements, including the generally unreported job that Capone held between his Brooklyn and Chicago underworld careers. It seemed all too legitimate for the young tough. He had taken his young wife and new baby to Baltimore where he worked, in daily suit and tie, as a bookkeeper for a construction company.

But following the death of his father Gabriele in 1920, young Al assumed the patriarchal role for his mom and siblings and finally moved to Chicago and a job offer from his early mentor, Johnny Torrio.

The author chronicles the persistent irritations of J. Edgar Hoover as recorded in his various notes. He didn’t want his FBI involved in any Capone and bootlegging investigations because he wasn’t sure he could win the day--and yet he didn’t like to see anybody else get any credit.

Bergreen also rips away--as many historians have--at the pristine image of Eliot Ness, who has enjoyed one of the greatest publicity coups of the century. Readers may recall that it was young sportswriter Oscar Fraley who, two years after Ness’ death, tookNess’ flat, unpublished autobiography (several original passages are published here), pumped it full of hot air and released it as “The Untouchables.”

Bergreen tries, not entirely with success, to interweave all these characters and events. He presents a lot of sourcing for his assertions, although his logic often hippity-hops around. He’s longer and wordier than he needs to be, primarily because he tends to adore some of his research and can’t let it go unwritten, even when it’s not to the point. And, whereas he avoids the temptation to use the bloody jargon of 1920s Chicago, he sometimes drifts into a scholarly mood.

But for those readers looking for some action, this isn’t to say that it’s short on blood. Bergreen recounts some of explosive moments in this volatile life: how Capone won his scars, the infamous baseball-bat murders, the Valentine’s massacre, assorted assassinations and other atrocities.

Somewhere in there is the essence of Al Capone and despite his ruthlessness, somehow we begin to understand him here (or think we do) and somehow feel his degradation in Alcatraz and his fading seasons. Maybe we like to see our mighty fall, but we don’t like to see them degraded.