"Go with the flow," that bit of '60s pop psychology, advises us to be at one with life's currents and eddies, to wash along with whatever outside forces prevail, to spare ourselves the frustrations inherent in resisting the inevitable.

A behavioral scientist at the University of Chicago has another, quite different, definition of "flow." To him, it is something that wells up within us when we are performing at optimum level. It is a kind of effortless mental efficiency. We don't "go" with that kind of flow. We summon it unconciously, experience it and feel good as a result of it.

In a state of flow, we become fully absorbed in an activity and lose track of everything else -- our bodies, our emotions, the passage of time and all sorts of other distractions. Flow is the opposite of boredom; it is the absence of anxiety. It happens when we match our skills to a challenge.

Flow may even explain why we occasionally feel "high" without any narcotic working on us but the rhythm of our own mental and physical effectiveness, although that line of reasoning remains purely speculative.

Psychologists around the world are looking with excitement at the studies of flow coming out of the University of Chicago, and many of them believe the behavioral scientist's research team is on to something big.

The scientist's very name suggests that he will not go with the particular flow that compels some people to defy family heritage and call themselves something simple. He is Mihaly Csikszentmihalyi, (pronounce it "chick sent me high") and that can be shortened only by friends who address him as Mike. He tolerates that, because Mihaly means Michael in his native Hungarian.

"He's going to be thought of as one of the most important social scientists in the last half of this century," predicts Howard Gardner, the prominent Harvard research psychologist. "He helps us see something we knew intuitively but could not put into words. He has a way of not only getting at issues people really care about, but he is able to approach those issues in a (scientifically) viable way."

Mike Csikszentmihalyi's studies, conducted over the last 15 years, are beginning to refine the definition of flow and to reveal the circumstances that permit people to experience it.

In his initial project on the subject, he examined the activities and motivations of rock climbers, chess masters, dancers, basketball players and composers. His findings were published a decade ago in Beyond Boredom and Anxiety (Jossey-Bass).

His next project focused on teen-agers and employed the unusual research technique that intrigues Gardner and other peers: He equipped 10 suburban Chicago high school students at a time with beepers. His research team set off the beepers at random periods during the day, and the students then recorded, on special questionnaires, their location, their activity and their emotional state. He and co-author Reed Larson turned the results into Being Adolescent (Basic Books).

Currently, 82 adult volunteers working in a wide assortment of fields are responding to Csikszentmihalyi's beepers and helping him further refine his theories. They allow him to examine their everyday behavior as it is happening. No one in his field had ever tried and succeeded at such a technique.

"Accepted scientific methods dictate how behavior is studied in America," Gardner says. "Mike has dared to study how people actually experience their feelings. Usually, we read about these things only in literature because we often don't know how to investigate subjects that fall beyond the reach of standard methods of study. He has let the problems dictate the methods, rather than vice versa."

The other day, Csikszentmihalyi adjusted his half-glasses and bent his sandy head over a questionnaire filled in by one of his teen-age respondents. "I have been charting her moods to see how they go up and down during the week, depending on what she's doing," he said.

"For instance, in the orchestra, playing the violin, that's when her mood is best. Studying a history assignment, thinking about other things -- alone -- that's her worst time of day."

The girl's response doesn't interest him so much as does the fact that he elicited it at a particular time and place and can therefore make it part of a graph charting the precise moments and circumstances of moods and activities. Combining it with other graphs, he deduces a pattern that cannot be duplicated by mere interviews or electronic brain scans.

On a superficial level, it might seem as if Csikszentmihalyi's hundreds of questionnaires document the obvious: Teen-agers are most highly motivated when idling with friends or engaging in a hobby, least motivated in the classroom, most depressed when isolated, happiest when listening to music or strolling in the park. Okay, but where does the flow come in?

"This research taught me how painful it was for people to be alone," he says. "All the moods seem to jump off the track the moment they leave the company of others.

"My students and I are working with teen-agers highly gifted in mathematics, music, science and other fields, and what we found, over time, is that many, many of these kids will stop using their talents.

"They get too discouraged, too depressed, when they are alone. They go home, drop their books and immediately leave. They try to find their friends and hang out, spend their time doing nothing that's structured, nothing that requires any concentration. They're having a good time, but in order to have a good time, they cannot be alone.

"The key to success is tolerance for loneliness. Being alone is a drag for everybody, but some of the students are able to sustain a certain amount of flow experience, even when they are working alone.

"They have somewhat less of a good time altogether, but at least they are able to study for significant amounts of time. On the average, they can spend 10 hours more a week studying alone at home than the other guys."

Csikszentmihalyi's definition of flow came out of those earlier interviews.

"I was astonished," he says, "to find that all those different people -- rock climbers, basketball and hockey players, dancers, composers, chess masters -- used very similar terms to describe their activities and the reasons they got so much out of them.

"They were describing it in terms of focusing of attention, the disappearance of self, the disappearance of the sense of time, the clarity of goals, the clarity of feedback. I call it the flow experience, because the people frequently used 'flow' in describing how they felt."

Flow, he discovered, involves a delicate balance between challenges and skills, boredom and anxiety. If the challenge is trifling, we become bored. If the challenge calls for more skills than we have, we become anxious, and that leads to avoidance.

"When people are bored, they're still fairly motivated," says Csikszentmihalyi. "Boredom allows more motivation than anxiety. For instance, flow is kind of like heroin to the surgeons we've studied. They can't take a vacation. After two days in Acapulco, they're so bored that they volunteer to do operations at a local hospital."

In 80 percent of cases studied, he says, time seemed to move much faster during flow. "But there are flow situations in which time moves more slowly, and you make a number of perceptual distinctions that you would never make in everyday life. The ballet dancers said some movements are so difficult that the first time they accomplish them, they are aware of every microsecond, and the movements seemed to take forever."

A few articles about his work have suggested that Csikszentmihalyi has uncovered a new source of euphoria, similar to the "high" often reported by marathoners. He refuses to indulge that notion because the data aren't in. Euphoria-inducing hormones may come into play, but no one knows if they are triggered by mental absorption or if the hormones set off the mental absorption first.

"Everything has a physiological basis, but it's not clear what the cause-and-effect relationships are. We know there's a connection, but who is to say that the mind rules the physical brain or that the brain rules the mind? What we think, how we think and how we feel affect our physiology just as much as the other way around."

His own research indicates that the pleasant feelings of flow are remembered, rather than consciously experienced. And, unlike the surgeons, many of the respondents could not anticipate a good flow experience beforehand.

One successful rock climber told Csikszentmihalyi that he dreaded taking on each new cliff. "He said it was like thinking about jumping into a cold pool of water. He would try to postpone the activity, avoid it, make excuses.

"Writers often say writing is so painful that nobody should try to do it for fun. But what they are describing is the preparation for it and the struggle in the first hour or so, before they really become involved. They actually enjoy writing, but they don't think about the enjoyment while they're doing it. The flow masks the quality of the experience because they're not so conscious of self."

Csikszentmihalyi finds his own flow by tracking and charting all those people out there who hear their beepers go off and pause to describe their feelings. management consultants later may use those findings to enhance the classroom and the workplace.

"We're beginning to realize that flow is not a good thing by itself," he says. "It's a powerful thing, like fire. Fire is great if you use it to heat your home, but if you are careless or malicious with it, you could burn down the house.

"Juvenile delinquents often say they did something destructive for 'kicks,' and when they describe 'kicks,' it sounds exactly like flow. They didn't have the skills to do anything challenging, except break a window or steal a car.

"Even if skills are channeled in the right direction, it's important for people to have more than one set. If you become too addicted to one or two narrow flow experiences, maybe you'll go home and become bored with your family.

"It's also important to make even ordinary experiences more flow-like. Instead of ignoring the 'boring' kids, find an activity with your children that puts you at more or less the same level, such as fishing or video games. Most people think family life is something that can be done naturally, that it will take care of itself. It won't."