New York ? It’s the format of the future. Or the flavor of the month.

Either way, you’re gonna know Jack.

Radio’s hottest new programming trend, most often compared to broadcasting an iPod on shuffle, is creating a buzz on stations from New York to Los Angeles.

Bruce Springsteen followed by the Beastie Boys? Led Zeppelin and Black Box? Elton John and Jet?

Yes, yes, and yes.

Such genre-bending mixes of songs, once derided by radio programmers as “train wrecks,” provide the format’s foundation.

“It’s everything from Elvis Presley to the Black Eyed Peas,” said Rob Barnett, director of programming for Infinity Radio and its eight Jack converts.

But it’s more than that. The new format peddles attitude along with music, presenting itself as a voice of unfettered expression in an era where corporate radio serves up micromanaged playlists. (Forget that Infinity – part of the Viacom media conglomerate that includes CBS, Paramount, MTV, among many other outlets – owns 180 stations.)

Jack, according to its boosters, is different. Its mantra is “Playing what we want,” offering hits from the ’70s through the present. It aims for listeners in the lucrative 24-to-45-year-old demographic, using a 1,200-plus song library that’s often six times the size of a typical station’s choices.

Veteran New York City disc jockey Bruce Cousin

Since Denver’s KJAC-FM became the first U.S. station to go Jack in April 2004, the format or one of its variants – there’s radio Bob and Mike, and a country version called Hank – quickly spread to Boston, Kansas City, Indianapolis, Baltimore and Dallas.

Infinity switched to Jack in Los Angeles on St. Patrick’s Day, followed by instant format makeovers in Chicago and New York that stunned longtime listeners in early June. Denver and Dallas’ KJKK-FM showed major ratings boosts within months of making the move.

Yet radio analysts were not fully sold on the idea hatched three years ago by programmers in Canada.

“I see the Jack format as theoretically well-intentioned, but very difficult to execute over the long term,” said Michael Harrison, founder of the trade publication Talkers magazine. “To find a mix that gets a significant market share is a very difficult thing to do.”

Scott McKenzie, editor in chief of the Billboard Radio Monitor, agreed that finding the right songs remains a formidable task.

“People say, ‘It’s just like an iPod on shuffle.’ Well, whose iPod?” McKenzie said. “It’s still very programmed. What you’re going to hear depends on the market.”

Before Jack, there was Bob. Canadian radio programmer Howard Kroeger was at a friend’s 40th birthday party when he quizzed some fellow thirtysomething party guests about the music blasting from the radio.

Their answers convinced him of an untapped audience for the greatest hits of the ’70s and ’80s, from Rod Stewart to Al Stewart to Amii Stewart.

Kroeger’s CFWM in Winnipeg was an instant ratings winner after its March 2002 debut as Bob Radio. Jack FM debuted that December in Vancouver, and American radio executives were soon listening intently.

Infinity soon turned to Jack, while another believer – Entercom Communications – switched to “play anything” formats in Boston (MikeFM) and Greensboro, N.C. (Simon Says).

“This is certainly what we consider phase one of a format that’s going to grow and mature,” said Barnett.

About 60 percent of the Jack stations operate without disc jockeys, raising concerns with the on-air talent’s union, the American Federation of Television and Radio Artists. But Infinity’s Barnett speaks of Jack, the format, as if it’s a living, breathing entity.

“Jack is honest,” he said at one point. “People want to hear what Jack says next.”

The biggest uproar over the conversion to Jack came at WCBS-FM, where Infinity pulled the plug on the nation’s No. 1 oldies station after 33 years. “BLOODBATH,” cried a New York Post headline, while listeners demonstrated outside the station.

Ousted with the format was Hall of Fame disc jockey “Cousin Brucie” Morrow, who quickly signed with Sirius Satellite Radio – but not before charging the changeover was a business decision that sucked the soul out of New York’s home for Motown.

“It’s the work of slide-rule guys, and it’s a miscalculation,” he said. “It’s the counters looking at the beans on Madison Avenue. I warned them, ‘This is going to come back and bite you bad.”‘