Le bernadin is a Manhattan restaurant with a $42 prix fixe lunch that, according to Zagat, serves "the best fish in N.Y. and maybe the world" and offers an elaborate menu over which local gourmets love to meditate.But when I lunch ed there Tuesday with Kent Brownridge of Wenner Media, Mr. Brownridge wasted no time making his selection (an excellent lentil soup and fish). "I can't be bothered reading through all that stuff," he said. "I ask for the special s and I order."In the decidedly offbeat world of Jann Wenner and his enormously successful flagship, Rolling Stone magazine, Kent Brownridge is an understated surprise. I don't know what I expected, but what I got was a tall, lean , bespectacled gent in his fifties, wearing a dark suit (the only rakish note a European-looking overcoat that suggested loden), and resembling not so much the senior VP who effectively manages Wenner's media empire, but the chief financial officer of a company on the Forbes or Fortune list (he's actually a vet of California electoral politics and helped run two presidential campaigns).But then, says Brownridge, neither is Rolling Stone precisely what people think it is.He's been with Wenner since the early San Francisco days (the offices were in the funky but absolutely right Embarcadero district; now they're on Sixth Avenue's TV Row in Manhattan) and Brownridge says, "Jann always i nsisted, `We're not underground; we're mainstream. Even if I can't afford coated paper and have to use newsprint.'*"In the past year Brownridge has probably been more hands-on in running Wenner Media than ever. There was the highl y publicized marital split of Jann and wife Jane (a key staffer and, through her parents, an investor from the very start) and his new relationship with a young, male Calvin Klein exec, a situation which I gingerly referred to as ` `the excitement." Kent didn't say much about that but did explain why Jann hadn't been seen much recently."He had a bad back and eventually a very serious spinal operation and really was out of the office for nearly six months." The problem derived from motorcycle riding and skiing and the operation involved the fusing of vertebrae and surgical transfer of a chunk of hip to the backbone. None of which sounds terribly pleasant.But as of last Tuesday Mr. We nner had just returned from skiing out West ("I don't think he was hitting too many moguls," said Brownridge). No motorcycling yet.And Jann is back in the office. "He drives everyone crazy. He's a real pain in the ass. He keeps trying to make the issue better and nothing is ever good enough. And when he's there, it shows" in the product.Wenner's newest, Men's Journal, is by any definition a hot book. Now five years old it boosted its rate base last year from 300,000 to 400,000 and just announced a huge bound upward to 550,000.As for Us, so long a problem child, it's now settled in with a monthly circulation of 1.1 million. "We got lucky with Us," Brownridge admits. "People was such a powerhouse and made so much money and then along came Entertainment Weekly and everyone said, you're gonna be squeezed between the two of them. But that isn't what happened. What happened was Entertainment Weekly created a c ategory. Until then no one knew what Us was, no one could define just what `entertainment' was." And new Editor Barbara O'Dair didn't hurt, either.As far as the flagship category is concerned, Brownridge thinks Bob Guccione Jr. ha s done a terrific job with his Spin. But he and Wenner don't worry about it. "Details (the Conde Nast book) and Vibe are the competition, especially since Bob Miller and Quincy Jones took it out of Time Inc."As for expansion, Ken t suspects the company will grow from within, as with Men's Journal. "Everything that's out there is priced out of sight or screwed up." He says they passed on John Kennedy's George. JFK and Jann had known each other for years, c ourtesy of Jann's friendship with mother Jackie. But Wenner passed; David Pecker didn't. Then, with the first issue of George out, Jann and Brownridge had a bad case of the morning-after blahs. "We underestimated the pull and popu larity of JFK." A year later, they feel better about having let it go. "It doesn't have an editor or a theme or a direction."And in his soft-spoken but take no prisoners mode, these Brownridge nuggets: Christie Hefner of Playboy is doing a swell job but, "I'm a little tired of Christie's First Amendment speeches. If a 7-Eleven doesn't want to sell your magazine, that's their right, too." Claeys Bahrenburg's $450 million acquisition of Petersen is a "fl ip" situation, meaning the company was bought to be sold. "And was it worth 450 to start with?" Another "flip," as Kent sees it, "Bill Reilly's K-III Media." "Can I quote you on all this?" Sure, said Brownridge, "They all think I'm an [expletive] any-way."