NEW YORK -- Here in the wilds of east Greenwich Village, where the natives are trendy, Irma Zandl ventures in search of the new. Like an anthropologist with a shopping fetish, she scours record stores, bike shops, clothing outlets -- any place teenagers are likely to congregate and consume.

Entering a vast hair-cutting emporium called Astor Place one afternoon, Zandl does a quick circle of the chairs, making mental notes as barbers shave peace symbols and geometric designs into the scalps of teenaged boys. "Pretty mainstream stuff," she murmurs.

Later, on a crowded stretch of Broadway, she suddenly stops, captivated by a window display of colorful, oversized shoes with soles that protrude like the edges of a bumper car. Zandl pronounces these "like, totally fantastical."

This piece of intelligence could be serious news for Nike, Reebok and anyone else who sells $125 sneakers. If Zandl's instincts are on target, every mall rat between Poughkeepsie and Pomona will be wearing big dumb shoes within a year or two.

Zandl's opinions on such matters are taken to heart by such companies as Reebok International Ltd., McDonald's Corp. and PepsiCo Inc. In one fashion or another, the nuggets she gleans from interrogating kids in shopping malls or from clandestine observation at the beach eventually make their way into sales pitches aimed at the MTV generation.

Her influence on the way companies sell to teens is subtle yet ubiquitous: It was Zandl who recommended, for example, that advertisers use rap music five years ago; now even orange juice makers have got the beat. Long before Earth Day, she suggested that environmental themes held a strong appeal among teenagers. Zandl also provided early warning on such teen fads as tie-dyed clothing, oversized denim pants, peace signs, Lycra bike shorts and day-glo colors before they were in K mart.

"She's able to translate what's happening in that world into terms that a marketer can understand," said Whitney Baldwin, a product manager at Warner-Lambert Co., who worked with Zandl at Johnson & Johnson. "She's not in some ivory tower somewhere looking down on them. She's out there."

Said Procter & Gamble Co. brand manager Brian Sroub with a touch of awe: "She actually knows how to talk to kids."

Knowing that goofy shoes are coming in or that ponytails (on men) are going out is no small matter to youth marketers. Although the number of teenagers has declined since the baby boom peak of 15 years ago, young people are richer than ever thanks to rising wages and generous parents. The 27 million kids between the ages of 12 and 19 will spend an estimated $79 billion this year, according to Teen Research Unlimited, a Chicago-area firm. That makes the American teen market larger than the entire economy of Argentina.

What's more, teenagers, unlike their more stodgy elders, are almost tabula rasa to product pushers. By hooking teens on a particular line or label, many firms hope they can build, in the cynical jargon of marketing, "brand loyalty" -- a lifetime of habitual consumerism.

Yet that's easier said than done. Knowing the language of the young can be tricky, especially when teenage sensibilities change faster than you can say lambada. "It's hard to run a business and stay on top of what kids want," said Aaron Kennedy, a marketing manager at PepsiCo. "... Once you get out of college, you're in a different world from them." Kennedy, who is all of 26, said even he struggles to stay "teen literate."

Which is a major reason that companies are willing to pay Zandl $2,000 a day -- she'll gross more than $400,000 this year -- to give them an up-to-date reading on teen slang, gestures, music and mind-set. Zandl, for instance, counseled Levi-Strauss Associates Inc.'s ad agency against continuing its campaign featuring gritty, urban scenes (some teens found it too depressing) and advised an acne-medication client against using wrestling in its commercials (too "blue collar," not hip enough).

With her omnipresent black wardrobe, white-blonde hair and Kabuki complexion, the 40-year-old Zandl looks like a cross between Morticia Addams and pop star Billy Idol. German-born but raised in a small Australian town, Zandl thinks her offbeat look helps her establish rapport with young people, whose speech affectations occasionally creep into her own. "I don't think they perceive me as, y'know, an authority figure," she said.

Indeed, to hang around with Zandl for a day is to feel hopelessly adult. Her conversation teems with the flotsam of the youth culture -- rock groups you've never heard of, fads that came and went unnoticed. She can discourse on a New Age massage technique called foot reflexology (the next big deal, she promises), or a natural antiseptic additive called tea tree oil (ditto). She is at home cruising through places like Unique, a self-consciously funky shop in Greenwich Village, where plaster dummies of Fidel Castro and Mikhail Gorbachev adorn the rafters and fixtures are spattered with graffiti.

"I find this fascinating," she says, barely audible above the store's pulsating sound system. "Maybe it's because I'm not another teenager."

In addition to her field research, Zandl conducts a half dozen or more focus groups a month with teenagers around the country. Through her New York firm, Xtreme Inc., she also periodically queries a standing panel of 1,000 young people about everything from their favorite brand of deodorant to whom they'd like to be for a week (recent answers included God, Donald Trump and "my mother").

In seminars she gives for corporate executives, Zandl stresses that not all teenagers are created alike. Their attitudes, and hence their buying habits, are shaped by six youthful trends, she says: materialism, New Age spirituality (such as environmentalism), the dysfunctional family, "traditional" values, and black and Latino culture.

Zandl, who began consulting five years ago after working in marketing for the L'Oreal Cosmetic division of Cosmair Inc. and Revlon Group Inc., has obvious respect for the intelligence of her research subjects ("It takes incredible talent to play Nintendo," she said earnestly). But she also characterizes them as insecure, socially conservative and even somewhat reactionary.

Many of those in her survey, for example, express reverence for the 1950s, which they perceive as a time when the nuclear family was strong and gender roles were better defined. As a result, they deem family dramas and family sitcoms as their favorite TV shows, especially those featuring traditional families such as Bill Cosby's -- a reaction, Zandl believes, to the difficulties young people face in their own homes.

The nostalgic streak manifests itself in teenagers' social behavior as well. "The boys are more macho than they've ever been," she said. "The girls are into nurturing. ... I think what happened to young people in the '70s and '80s was unnatural. It is unnatural to make a sensitive male. I've never heard any {teenager} say, 'I wish my father were more sensitive.' "

In fact, Zandl's research seems to belie two assumptions about young people: that they are instinctively rebellious and unfailingly optimistic. A majority of her survey group say they expect life in the United States to deteriorate and that racial, religious and sexual bigotry will increase as they inherit the world.

Teenagers, Zandl observed, "have very little to rebel against. I mean, most of them are having their first sexual encounter at home because their parents aren't there" to object. She added: "They don't want to stand out. They're insecure. ... Very few girls want to look cutting edge. Basically, they want to look like Christie Brinkley."

The cautiousness comes through in their attitudes toward drugs and sex as well. During a recent Zandl-run focus group, Procter & Gamble's Sroub said he was struck by the "wholesomeness" of the assembled teens on both subjects.

"There was a lot lower level of sexuality than you would have thought," he said. "Maybe kids are more conservative than we think. Or maybe they were just afraid of getting caught."