n a white-sky November day, Wes Anderson is lounging in a darkened studio in the Brill Building, formerly the silvery hub of Tin Pan Alley. His slight six-foot frame, all 155 pounds of it, is decked out in undersize beige corduroys and an undersize beige shirt; his auburn hair, once unruly, has settled into a subtle and rather stylish alliance of tamed cowlicks. ''We're doing a weird little recording session,'' he quietly explains. ''Yesterday, our editor was whistling along with the soundtrack, and I thought, Wait -- that's good!''

Anderson immediately realized that this was a perfect touch. It matched the sound in his head that, somehow, this crucial scene lacked. So, at this late stage in the editing process of his new movie, ''The Royal Tenenbaums'' -- and despite the fact that the Brill Building is teeming with musicians -- he has enlisted a ragtag assortment of crew members to lay down a whistling track, which will then be added to the score.

Dylan Tichenor, the editor of the film, steps up to the microphone first and blows out a shockingly off-key version of the melody. No one whistles well under pressure. Tichenor jokingly calls for a mimosa to loosen him up, but Anderson is not on terms with defeatism. ''No, no, that's really good,'' he keeps saying, albeit tentatively. ''Try it again, and leave a space for a bigger breath before the dramatic part. And do that Disney sound you were doing yesterday.''

Listening to the soundtrack in headphones and staring up at a screen flickering with Gene Hackman's muted image, Tichenor tries seven more times, but his shower-and-household whistling talents have abandoned him. ''Try a few more runs -- they can adjust the pitch later,'' Anderson says.

''I'm nervous, man,'' Tichenor jokes. ''My lips are shaking.''

Even in these tense weeks of postproduction, Anderson doesn't seem to have a care in the world. ''It's important to remember that no one expects you to be a professional whistler,'' he says.

Tichenor is unconvinced. But Anderson stands in front of him, backlit by the glow of the screen, and closes his eyes to listen. Tethered like an astronaut to his own headset console four feet away, he conducts his tuneless virtuoso with crisp, happy Mitch Miller gestures, each of which concludes with a swirly little flourish.

''The Royal Tenenbaums,'' opening Dec. 14, is a tale of familial dysfunction, failure and redemption. But that rough description belies its peculiar sense of joy. The three children of Royal Tenenbaum (Hackman) and his wife, Etheline (Anjelica Huston), are child prodigies: a 12-year-old playwright, a tennis champ, a boy financial whiz. But two decades later, after the separation of their parents and other mishaps, their promises of glory have turned to dust. Royal, a charming but reprehensible lawyer, hasn't seen his family in years. The movie is set in a storybook New York and chronicles Royal's comical schemes to win back his place in the Tenenbaum clan. In the scene Anderson is now tweaking, Hackman plays for sympathy by announcing that he is terminally ill.

Looking on as Anderson spryly conducts Tichenor's hapless performance, I'm reminded why the press sometimes treats the 32-year-old director like a nifty kid who happens to make swell movies. Judging from appearances alone, he's an easy mark. He addresses the world through clear-framed spectacles and with the diffidence of a grad student; he carries his credit cards bundled together by a rubber band. During the ''Rushmore'' shoot, one actor recalls, ''he would always have only half of his shirt tucked into his pants -- always. Only half. The other half would be hanging out casually.''

Anderson may straddle the worlds of adulthood and childhood, but he's hardly a case of arrested development. His work is not the product of emotional immaturity; quite the opposite. The appeal of movies like ''Bottle Rocket'' and ''Rushmore'' (with its reverence for stamp collecting, Swiss Army knives and BB guns) comes from the fact that Anderson has retained a boy's way of conceptualizing the world -- but he conveys it with a sophistication that a boy could never articulate. By exercising meticulous control over his films' characters and structure, he recreates the fun and cruelty of youth in a lexicon that real adults have forgotten and real children have yet to acquire.

The tone of elation in Anderson's movies relies in no small measure on the careful little touches -- something as seemingly minor as 23 seconds of whistling. Which makes this odd recording session anything but frivolous, despite Anderson's sunny sense of calm.

''What ever happened to those old Disney whistlers?'' he muses. ''Weren't they great? Are there whistlers like that anymore?''

One of the crew suggests that they try Meryl Streep; after all, she'll be in the building Monday to loop another film. ''I bet she could whistle,'' Anderson says wistfully. ''She certainly can belt out a song.''

Inside a studio, Wes Anderson moves gingerly, like a man afraid to wake a sleeping child. But outside its shadowy confines, he is nimble. He arrives at his Upper East Side address late one night after another long day of editing, clambers up the stairs two at a time and enters his apartment. He sweeps past a giant ''Alphaville'' poster into the bathroom and begins brushing his teeth.

I'd been warned about Anderson's living habits. James Caan, who played a pivotal role in ''Bottle Rocket,'' recalls that after the first day of shooting, he stopped up to see Anderson in his hotel room. ''I've never seen so much stuff in my entire life,'' Caan says. ''I looked around for Wes, and there he was, looking like a pinky in clothes. If you go to his house, bring a searchlight.''

Anderson's place looks like a prop-storage warehouse. Instead of mementos or family photos, the apartment is scattered with relics from his films: a Stetson hat from ''Tenenbaums,'' a Cousteau book from ''Rushmore.'' A large painting of Winston Churchill -- also from ''Rushmore'' -- smiles down on the living room from above the fireplace. One of the few traces of noncinematic life are volumes of Jules Verne and Robert Louis Stevenson that, judging from the Dewey Decimal coding taped to their spines, appear to have been cadged from a library somewhere.

''Oh, those aren't real,'' Anderson says after emerging from the bathroom. ''They were made to look that way by the 'Rushmore' art department.'' On inspection, it turns out they've been cleverly disguised as library books, right down to the fake date-stamps inside the back cover, detailing when nonexistent students checked them out. They're never shown in the movie and call to mind the old story about the director Luchino Visconti, who insisted that cabinets in his scenes be filled with exquisite china, even though their contents were never going to be seen on camera.