TV PREVIEW

"Inside the American Mob", 9 p.m. Sunday, National Geographic Channel.

A gritty six-part series, “Inside the American Mob” chronicles the decline and fall of the Mafia from its apex of power and influence in the ’70s to its virtual dismantlement two decades later.

As the rub-out begins (with back-to-back episodes), the New York-based Five Families - Gambino, Colombo, Genovese, Lucchese and Bonanno - have a vise-grip on their far-flung criminal enterprises.

They use an organizational template devised by Mob architect Lucky Luciano back in 1931. A strict tradition of ethnicity (all “made men” must be 100 percent Italian) and vicious intimidation has kept them impermeable to infiltration by law enforcement agents.

“Inside the American Mob,” which debuts Sunday, maintains that a variety of factors altered the blood-soaked playing field in the ’70s, beginning with a generational shift on both sides of the fence.

These were no longer your nonno’s goombahs, being trailed conspicuously by feds who dressed and looked like accountants. A few sheepdogs were able to slip into the wolf pack.

The second episode, in fact, is built around Joe Pistone, the FBI agent who spent six years deep undercover as Donnie Brasco, long enough to gain a position of trust in the Bonanno family.

The Cosa Nostra also rotted from the inside, as the inviolable rule of omertà (the Mafia’s legendary code of silence) began to dissolve. Even high-ranking gangsters like Sammy “the Bull” Gravano and Joe Massimo were betraying the no-snitch oath.

The documentary also suggests that taking down mobsters became something of an obsession for the Justice Department and the FBI during this era.

The series doesn’t devote as much attention to other significant changes, such as the development of sophisticated eavesdropping devices and the emergence of dons, like Joe Colombo and John Gotti, who seemed to actively court the spotlight.

The story is told by a procession of talking heads, including federal prosecutors like Rudolph Giuliani and Louis Pechini, as well as former mobsters, some openly displayed, others with their appearances obscured.

“Inside the American Mob” also effectively employs dramatizations and abundant archival and surveillance footage. (It’s a blast to see those giant gas-guzzlers of yore floating around the streets.)

The Philadelphia Inquirer’s veteran crime reporter George Anastasia assumes a primary presence in next week’s episode, “New York-Philly War,” detailing the reign of terror that subsumed the Philadelphia Mafia after the seismic assassination of the city’s “Docile Don,” Angelo Bruno, in 1980.

With rival factions eager to claim the corrupt boomtown that was Atlantic City, Nicodemo Scarfo ascended to Boss, unleashing a brutal string of murders (18 in four years). Scarfo’s rule was so ruthless that two of his closest associates, including his nephew Crazy Phil Leonetti, flipped, becoming extremely productive witnesses for the government.

The documentary identifies this development as the turning point in the Justice Department’s crusade to snuff out the Mob.

The most salient impression left by this series is that the Mafia operated as a sleazy, brutal pyramid scheme in which lower-level criminals all kicked money up the ladder, and the most prized subordinate was an “earner.”

Both the substance and style of “Inside the American Mob” are familiar. The gang-busting narrative hasn’t changed much since Walter Winchell was barking out the voiceover for “The Untouchables” half a century ago.

But this is a solid addition to a saga we find endlessly fascinating. Insider accounts of the Mafia are like a scary bedtime story we like to hear over and over while cuddled up in our blankets.