Who is happy? Until the past decade or so, psychologists didn't have a good fix on happiness -- who, how much, or why. That may be because psychology traditionally has been too busy trying to measure misery and alleviate suffering to study the upbeat.

Lately, however, a movement within the mental health field toward "positive psychology" has spurred a quantum leap in research to understand happiness. Although depression has been on the rise for decades and other social indicators seem down in the dumps, what psychologists are finding, surprisingly perhaps, is that most people are at least moderately happy -- regardless of age or gender.

"When you go out and randomly sample the world at large, people present a happier picture of life" than you might expect, says David Myers, professor of psychology at Hope College, in Holland, Mich., and a leading researcher of happiness.

National Opinion Research Center surveys periodically report consistently the same levels of happiness: Three in 10 Americans describe themselves as "very happy," six in 10 say they are "pretty happy," and only one in 10 reports being "not too happy," says Myers.

Other polls get similar results. In a 1998 survey, nearly half of 1,003 American adults judged themselves to be happier than Oprah Winfrey, Bill Gates, the Pope and Chelsea Clinton. Without discounting that sad times and sad events occur in people's lives, Myers says, "By and large, most people live with positive emotion from day to day."

Myers and other psychologists have taken the study of happiness even further, identifying the traits that commonly mark happy lives and the changes people can make to be happier. "There are genetic predispositions to happiness," says Myers, author of the 1993 book "The Pursuit of Happiness: Who Is Happy and Why" (Avon, $12). "I liken happiness to cholesterol levels: Both are genetically influenced and yet both are, to some extent, under our control. By diet and exercise, we have some influence on our cholesterol levels; likewise, there are certain things we can do that will have a bearing on our happiness."

Probably foremost of the happy traits is positive self-esteem. Studies have found that happy people like themselves and believe themselves to be smarter, healthier, more sociable and generally better than the average person.

They also are optimistic, extroverted, and tend not to catastrophize when bad things happen. To turn that emotional corner, Myers advises that you behave and talk as if you feel optimistic, outgoing, and have high self-esteem: "Going through the motions can trigger the emotions."

Happy people also feel they are in control of their lives. How to get started? Myers advises taking control of your use of time -- by setting long-term goals and breaking them into daily aims.

Another important predictor: close relationships, such as "enjoying supportive, soul-mate friendships," like some people find in an intimate, secure marriage, says Myers, adding that deeply caring and loving relationships are a priority in the pursuit of happiness.

Happiness in work? In leisure activities? Mihaly Csikszentmihalyi says it correlates to what he calls the "flow" experience. The noted University of Chicago psychologist's research shows that achieving a state of mind in a task that mindfully engages one's skills and challenges them without being overwhelming increases one's quality of life. Several studies recently have found that the "zone" achieved in aerobic exercise not only improves health and energy, but is a natural antidote to depression and anxiety.

Study after study has found that religiously active people are happier. "They cope better with various sorts of trauma, and are less vulnerable to substance abuse and suicide," Myers explains, crediting in part the social support network that "faith communities" can provide. "We also know that happy people are less self-focused and less self-preoccupied than unhappy people, and there's speculation that religion may help turn people's eye off of self and onto a larger mission."

Religious faith for many provides meaning and purpose in their lives, he adds. "It's a source for feelings of ultimate acceptance and of an ultimate hope that come what may, in the end, all should be well."

Last, says Myers, upping your happy ante is as easy as putting on a happy face. Research shows, he says, that when "manipulated into a smiling expression, people feel better."