Hey, slow down, get laid back, take some time to smell the roses.

We're talking about Southern California, here--the Home of the Hot Tub, the Mecca of Mellow.

It's like the slot machines in Las Vegas, they hit you with it right at the airport. You're not even out of the parking lot in your rent-a-car, and you look in your mirror and see you're putting out enough smoke to kill every medfly in Orange County. Something is terribly, terribly wrong. You find a pay phone, you call back to the rental desk, you start screaming.

"Hey," says the girl with a little chuckle. "Maybe it's a diesel."

It isn't, but relax. Lighten up. Showing stress in California is like smelling bad anyplace else. It isn't done.

This is very hard on people from the East Coast. It's the way of talking out there that drives you crazy. It's like everybody did an apprenticeship at a late-night FM station, the kind where they play "Sweet Little Alice Blue Gown" done very slowly by 1001 Strings. But there's something wrong, something . . . Whatever it is, lay back. Smell the roses.

It gets to be a philosophy of life.

It's the waitress at Moustache in Hollywood who sits down at the table with you while she adds up the check.

It's the two guys talking at the bar at Barney's Beanery.

"My psychiatrist says I'm still in love with my wife," says one.

There's a long pause of the kind that's disturbing to Easterners, especially New Yorkers who've been trained by delicatessen countermen who fill the slightest pause with shouts of "What else?"

Then the other one finishes nodding and asks: "Who's your psychiatrist?"

It makes everybody seem so nice, so relaxed--just the way we've told ourselves that we're supposed to be. It seems that Californians have found a cure for what we think of as the disease of stress. Stress is the All-American disease. Anybody can get it. Like hypoglycemia (low blood sugar--remember when that was popular?) or the latest allergy, stress is spread largely by word of mouth. You hear about it, then you start thinking you've got it. Other ages had neurasthenia, chlorosis, melancholia, conniption fits or the vapors. We have stress.

Stress came along, conveniently enough, just as the American Psychiatric Association was voting that our old favorite, neurosis, didn't exist.

Not to worry. Just as Freud's middle-class Viennese female patients got hysteria, and World War I soldiers got shell shock, we have stress-induced "burnouts."

Not only can anybody suffer from stress, it seems that everybody does, regardless of race, creed or anything else that gets you points in an affirmative-action program. Dr. Charles F. Stroebel, author of QR--The Quieting Reflex estimates that 95 million Americans "suffer from tension-related physical or psychological ailments." Colorado psychologist Randy Kunkel says "approximately 85 percent of the professional work force is at some stage of burnout at all times." Stress is big, stress has moved up the charts with a bullet. If stress had a Neilsen rating, it would be bigger than "The Winds of War" and the Super Bowl combined.

We now have stress clinics, tests and consultants. Even dentists--they took time off from talking half the nation's grownups into getting braces to discover stress-induced "bruxing," or grinding the teeth. We've got techniques for meditation, medication and relaxation. University of Pennsylvania researchers claim you can lower your blood pressure by looking at tanks of fish. (No one ever claimed it raised it.) Even better, become the fish yourself by slipping into the Denver police department's stress-therapy float tank, and bask for an hour in total darkness and tepid salt water.

There's an American Institute of Stress. We've had Police Stress magazine, edited by a Boston patrolman named Edward C. Donovan who has vanity license plates reading STRESS.

Wait a second--vanity license plates? It's enough to make you suspect that stress is fashionable.

Heresy, indeed.

But why else do we consistently take such pride in flunking those magazine tests for Type A personalities, meaning personalities susceptible to stress? For instance, one test asks:

Are you: Tense? Highly competitive? Plagued by deadlines? Subjected to many stressful events?

Who ever answers no? Discovering you're a Type A is like winning life's own letter sweater. Who can resist going out for the team?

Indeed, it's beginning to look like Type A stress is the lifestyle we crave. Of course. Easterners have always known this to be true.

he problem, here, is California. California, at first glance, seems to indicate that a stress-free life is possible. Type C.

It's an awful thought. Then again, it gives Easterners something to think about when they're in Los Angeles, listening to those purling- brook voices, trying to figure out what they remind them of. Sooner or later, somebody takes them aside and explains it.

For me, it happened one night on Sunset Boulevard when a screenwriter friend listened to me marvel at the conspicuous ease of Californians until he couldn't stand it anymore.

"Fear," he said. "It's just fear."

That voice . . . suddenly it all became clear. We've been getting the message wrong. Californians are way ahead of us. We hide our stress, they advertise it. That tone of voice . . . is precisely that of somebody who realizes he's locked in a room for eternity with, say, a rabid Doberman Pinscher.

Hey, man, relax. You've got your space, I've got mine. Slow down. Smell the roses. No stress. Attaboy.