MICK Jagger's been at it for going on 20 years. The wizzard of id. Jumpin' Jack Jive, love you live.

But the act is getting old. Seventeen albums and tens of millions of dollars later, Jagger's patter is so pat he seems tired of tough, too bored to improvise. Most people with such elaborate ennui would be ready to change their lives.

"I would," he says, "but I don't know what I'd do."

Meanwhile, Jagger adheres to the school of unsettling celebrityhood. Keep the audience guessing, treat'em rough. They can't always get what they want, but they get what he thinks they need -- a delicious discomfort.

Here in the poster-strewn 12th-floor office of his mid-town Manhattan record company, Jagger's studied antagonism is as impersonal and as fascinating as snake eyes.

Elbows poking out, leaning slightly forward, he uses his whole body the way Barbara Streisand uses her nose. There's no way to make it seem ordinary, so he accentuates its every angularity. Bent kneed, loose-limbed, he forses the eye to admire his self-possession; and all the while watches, with the intimate contempt of a Tulouse-Latrec danseuse , the effect of this provocation.

A photographer arrives, and instantly Jagger is pouting.

"Nobody asked about a photographer. You just announced it as a fait accompli . What are you going to shoot -- a roll? Maybe less? You're not going to get a good picture, you're just going to get a snap, right? There've been thousands of photographs, you can't get anything as good . . . All right, let's do it. Here's a white wall."

Jagger has perfected the posture of challenge. He flings himself against a blank wall, head rigid, bad shadows, mug-shot style. He deliberately draws his face into harsh lines. Like a threat, he stares right through the camera.

A few minutes later, Jagger cuts off the session with an emotionless "thank you." His press agent shrugs. "He knew about the photographer. He just likes to play around."

Jagger is wearing white socks and a joint behind his ear. White running shoes, a yellow shirt and turquoise pants with black stripes -- all just loose enough to suggest that he picked them up at a secondhand store. The Andy Warhol reverse-chic of a man who couldn't get thrown out of the Four Seasons in bathing trunks.

He is, apparently, in a good mood. The 17th annual Rolling Stones boys-and-girls-together album, "Emotional Rescue," has just shipped, and a half-dozen staffers mill through the offices in the anarchial plotting of promotion. Telephones rattle while the title song airraids from the radio. At Jagger's request, a Rolling Stones Records employe is scrambling up the figures on national airplay.

"Thank God that's finished," says Jagger, clanking down a beer bottle and jackknifing into a swivel chair. "Now I can go and do something fun ."

Jagger, Michael Philip. Born in Dartford, Kent, 7/23/43. Now of "London, Paris and New York, every 18 months in a cycle." Divorced; father of two 9-year-old daughters (one illegitimate). Trained in business administration at the London School of Economics, privately employed,

Mick P. Jagger. Performing is his middle name. For 18 years, Jagger has been polishing his role as the prancer/dancer/vixen of rock'n'roll. His Satanic Majesty, a street-fighting, pill-popping, rutting, strutting Dorain Gray, lithe and omnipotent and manipulative.

But it's all in fun, he says. All in the interests of entertainment.

"Everybody does it. People are always being what they preceive themselves being whenever. It's like a secretary and a guy who delivers meat or whatever. They go out at night as somebody else."

So Jagger will not distinguish his performing from his "real" personality. "Like Jekyll and Hyde," he says. "They're not seperate, are they? That's schizophrenia. They're dependent."

He spits out smoke in punctuation marks. The level of calculation of his eyes is straight from the poster for "A Clockwork Orange" -- not only the expression, but the lines under his eyes which are carved down in rays like those painted eyelashes. In the hazel iris of his left eye is a brown spot like a water stain on a photograph.

The familiar shadows in his face are more a matter of planes than wrinkles. In ordinary light, he looks 10 years younger. Ten years is a whole generation in rock'n'roll. By that measure, the Rolling Stones are the grandparents of the Pretenders.

They have achieved this venerabiliy with only two personnel changes (guitarist Ron Wood for Mick Taylor, who replaced Brian Jones), and without having irrevocably changed their style. They have, from time to time, incorporated a convenient commercial trend, but they have never lost control of it.

They negotiated the New Wave nearly high and dry, like experienced surfers of sound. They have dabbled in country-rock, r&b and Jamaican regae, like the Peter Tosh music the Glimmer Twins produce. But the fine spine of their black-blues rock'n'roll has never bent.

There's a serious mystery of contemporary culture here. Can a band fly for 20 years in the face of ephemeral fads? How do androgynous campers avoid the conservative backlash? How do you keep rock'n'roll alive while Le Freak and heavy-metal Frazetta-rockers are hammering the same four chords and disco shrills in the elevators?

Longevity, says Jagger, is a matter of "riding out" the trends in music. "Not ignore them. You can't ignore them any more than" -- laughing, he drops into the pseudo-sincere vowels of a gospel emcee -- "a ship can ignore the sea."

And by ignoring the currents, a band could run aground on its own material. "Just because you've been around a long time doesn't mean you're nostalgic. I don't even think most people go back much further than out last three albums. The Beach Boys are nostalgia [because] they're playing to that audience."

But Jagger claims the Stones don't play to anyone, that their audience cannot be classified. "They're not my 'peers' -- they never were. I'm not condescending to anyone. It's not like movies, where you have previews. Nobody does ratings or demographics on rock audiences."

Sometimes condescension is more profitable. In a buyer's market still dominated by single records, the Stones no longer hit the Top 40 week after week, as they did in the '60s. It's become a medium of formula, and Jagger does not writer to order.

"Some albums have a mood, which is the theme if there is any. The last album ['Some Girls'] had a mood that was like a theme. I didn't see it at the time, but I saw it later -- when it was pointed out to me." Jagger rubbers up his face invitingly like a bawd; "Some Girls" was roundly lambasted as a sexist-racist crock by such social critics as Jesse Jackson.

"An album is like a jigsaw puzzle. You put the pieces [the songs] into a box and you shake them up and see what fits."

Jagger is a businessman, an economics scholarship student, a tax exile from Great Britain who nevertheless managed to have his divorce decreed in London to avoid the California community-property pitfalls. He likes to know the figures on his albums, although he passes this off as a ploy to keep the accountants honest.

Yet he doesn't like to talk business. He reduces the band and its entourage and support staff to "a partnership of five people" with a short-term licensing arrangement with two conglomerates and two full-time roadies. The rest of the operation, he implies, is serendipity.

Mystery, illusion, elusion. Years ago, the band was on a cruise ship, cavorting obnoxiously and enjoying themselves hugely. A group of outraged older passengers (recounting this, Jagger adopts a high-sinus, stiff-lipped Oxford accent) asked what must have seemed to them a deeply serious question:

"What are you boys about? Give us a glimmer."

Jagger and Keith Richards shivered with delight; The Glimmer Twins were christened.

The Glimmer Twins have always been the eye of the "cross-fire hurricane." Grammar-school friends, they began playing with drummer Charlie Watts, bassist Bill Wyman and Jones about 1963 and released their first record, Buddy Holly's "Not Fade Away," a year later.

They were born front-page material: the originators of bad-boy rock, long-haired, scruffy, ostentatiously sexual. Jagger especially was hot gossip: Jagger and Christine Shrimpton, younger sister of London's most famous Carnaby Street model; Svengali Jagger and angelic-looking heroin addict Marianne Faithfull.

In 1967, after a raid on Richards' English country home, Jagger was sentenced to three months for possession of four pep pills, Richards to a year in prison for allowing hashish to be smoked at his residence. (Richards' conviction was overturned and Jagger's reduced to a year's probation.) The court proceedings included such nuggets as the revelation that Faithfull was wearing nothing but an 8-by-5-foot rug.

The prosecuting attorney: "Would you agree, in the ordinary course of events, you would expect a young woman to be embarrassed if she had nothing on but a rug in the presence of eight men, two of whom were 'hangers on' and the third a Moroccan servant?"

Richards: "Not at all . . . We are not old men. We are not worried by petty morals."

Hot stuff for 1967.

It was all going according to plan until 1969. That year, Brian Jones quit the band and shortly thereafter was found dead, floating in his swimming pool. Jagger was convicted on marijuana possession charges (Faithfull was acquitted). And in December, at the end of what was to have been a triumphal American tour, the Stones played Altamont Raceway. While the group played, a man died, and Altamont laid waste to the Garden of Woodstock.

With his St. Tropez marriage to Nicaraguan Bianca Prez Morena de Macias in 1971 (he wore a pale green suit, multi-colored sneakers and no socks; she wore a white "maxi" dress), Jagger entered the Beautiful People rolls for better or worse.

He made the International Best Dressed List. He celebrated his 29th birthday at a concert with a banana cream pie free-for-all. Chrissie Shrimpton tried to publish his 10-year-old love letters. "Hair" actress Marcia Hunt won a paternity suit; his marriage collapsed and Bianca Jagger wanted half of what she estimated to be $25 million.

Margaret Trudeau did not have an affair with Jagger, who has been living for several years with model Jerry Hall. A former bodyguard tried to steal $3,000 in cash and $10,000 in jewelry from Jagger's bedroom while it was occupied. Keith Richards faced a long prison sentence in Canada for heroin use, and the Stones periodically flirted with disbanding.

Finally, two years ago, the band emerged from a critical slump with the massively successful "Some Girls." Richards was allowed to play a benefit concert in Toronto instead of serving time, and the Stones began rolling again.

For all the years Jagger has been coming on to his audiences, he doesn't accept their intrusions gracefully. While he is talking, a delivery boy passes the open doorway and spots the singer. Several minutes later, a clean sheet of paper and a pen ready, he knocks at the door and asks for Jagger's autograph.

He signs -- a legible, no-nonsense check-signing signature -- without smiling. After the boy leaves, he yawns, "Duuhhhhh," mockingly.

That tired, unfocused hostility flickers in Jagger like St. Elmo's fire. Asking him a question is like waiting for Godot. Call it the Indian rope trick. He conjures up a seemingly solid ladder and then laughs when you fall off.

Will the band tour behind "Emotional Rescue"? "No."

Does he write songs as a piece, first lyrics, or first music? "Both."

Want to talk about the new album? "No."

Does he still feel about rock 'n' roll the way he did 15 years ago? Ten? Five? "Two?" he mocks. "I feel just the way I did two years ago."

Jagger's original good humor, dented by the autograph hound, is now nearly crumpled. He collects a staff meeting in the next room. He does not say goodbye.

There is nothing left in the executive-beige hallway but the record label logo: the slick red mouth, the leer that made Mick Jagger famous, tongue lolling, in five-foot plastic.