Joe Washington hums in the shower. He hums in the Washington Redskins' locker room. He hums at home. His teammates knew the running back had recovered from a nagging knee injury recently when his humming picked up.

"It relaxes me," Washington says of the sound he has made most of his waking hours since childhood. "I just do it."

In Heloise's Handy Book Calendar/Organizer 1985, America's foremost household tipster recommends humming a song while replacing ice-cube trays in the freezer.

"When I do, I never spill a drop," she writes. "It works, but darned if I know why. Does humming steady the hand? Or what?"

Three months ago, 350 people gathered at San Francisco Bay's Pier 2 to hum, simultaneously and nonstop in E-flat major, with 100 people in New York and another 100 in Seattle. Dogs nearby stopped barking. Pedestrians stared. Babies sat up in their strollers. It lasted for more than an hour.

The resulting sound was mixed together, via satellite, by radio station KQED-FM in San Francisco and broadcast to eight other stations and 250,000 hummers across the nation -- probably the largest single "hum" in history.

"We did it to create good sound and good energy," says Bonnie Barnett, a San Francisco composer who organized the event, Tunnel Hum 1984, and nine other formal hums since 1981. She says that its length and musical key arose naturally from the crowd. Her dream is to hold a planetary hum-in called Global Hum.

"People come out of a hum with so much exuberance," Barnett says. "When it's over, it's hard to get them to leave. I'd like to get people around the world humming at the same time."

Humming has been called "the world's greatest natural tranquilizer." It has been called an energy recharger. It has also been called a nuisance. For most people, the murmuring noise is one of life's insignificant quirks.

To hum requires no note reading, no ear for music, no talent. The physiological process is so humdrum that scientists at Montreal's McGill University once used it as a constant in voice experiments. All you have to do is put your lips together and sing -- without the words.

But the physiology of humming is far more simple than its teleology. The question isn't "How?" It's "Why?"

Although most hummers confess they don't know why they hum, answers are found in sources as diverse as ancient religion and clinical psychology.

Relief from anxiety and boredom is one answer. According to Mihaly Csikszentmihalyi, professor of Behavioral Sciences at the University of Chicago, activities such as humming, whistling and finger-drumming are examples of autotelic behavior. People do them for their own sake, not for external reward.

But they do provide internal rewards. Csikszentmihalyi's study, the basis of his book Beyond Boredom and Anxiety, analyzed diaries of subjects asked to keep track of "things they did for the heck of it." He labeled the patterned, almost unconscious behavior "microflow activity," and concluded it provides a sense of personal control by helping to shape experience.

"It's a way of giving structure and order to our environment," says Csikszentmihalyi. "Microflow activities like humming seemed to allow people to concentrate on something they were doing and cut out distractions of their surrounding."

To test his observations, Csikszentmihalyi conducted a microflow deprivation experiment. Subjects were told to stop humming and other similar activities.

"After about 24 hours . . . all of them reported very strange difficulties in everyday life," he says. "They walked into doors. They spilled coffee. They broke their eyeglasses. Many couldn't concentrate."

While the irritation of stopping habitual microflow activities probably contributed to the problems, Csikszentmihalyi says eliminating these individual control devices was like removing a boat's rudder.

Humming prevents more than clumsy accidents in Neil Anderson's Singing Man (H J Kramer Inc., $8.95). It keeps his characters sane.

In the novel, an American professor, a French news broadcaster, a Scottish judge and a couple dozen others suddenly, without explanation, can't talk without singing their words. When together, their "singtalking" speeds up uncontrollably, causing confusion and exhaustion. Humming slows them down and clears their minds. News reports tag them "hummans." Psychologists diagnose the phenomenon as a new form of mental illness, possibly a bizarre way to preserve individual identity in a dehumanizing world.

"Writing this book definitely got me humming from time to time," admits Anderson, a former vice president of CBS Records who gave up his career five years ago to write. "It sounds strange -- a 53-year-old man humming," says the Mill Valley, Calif., novelist. "But it has enriched my life."

Like Joe Washington, Anderson says he and his fictional characters usually hum no particular tune. And it calms them. "Sometimes, I just needed to tone down from writing, and out came this humming. It has no religious overtones. And it has no connection to music. If I find myself stressed now, I hum."

Some behavioral experts say the calming effects suggest humming to be "a centering technique," borrowing the term from meditation.

"We know that music works as an eductive device," says Linda Keiser, associate director of the Institute for Consciousness and Music Training Seminars in Baltimore, where therapeutic techniques using music are taught. "Music is able to bring things to consciousness. People hum to focus themselves. People hum to center themselves."

Keiser adds there is speculation that the vibration of some sounds, like the resonance of humming, serves a positive physiological function too. "It happens to singers," she says. "The reverberative quality can be very comforting."

Beyond physical comfort, research has linked certain kinds of sounds and tones to good health.

"Humming is another of those things generally considered unimportant," says Steven Halpern, a Belmont, Calif., composer, author and researcher. "But long before people were singing the words of popular tunes, they were making sounds to themselves."

Halpern's research focuses on the relaxation response and the healing potential of sound. He calls it "tuning the human instrument." He says people understand intuitively, if not consciously, that making sounds like humming to one's self is "psychotechnology" used for centering the mind and balancing the body.

"All the atoms and molecules in our bodies vibrate," says Halpern. "Scientists have been telling us, as did ancient yogis, that all of the cells, muscles, glands and organs in our body sing a sound on a physical level that we can't hear, but perhaps intuitively recognize.

"Humming may be a primordial way to tune into that -- assisting the body in balancing its own energy systems and bringing itself into a greater degree of harmony."

A sound-frequency therapy developed in Paris 10 years ago by Dr. A.A. Tomatis initially used sound to help autistic and dyslexic children. In its broader uses today, it employs a classic hum as an energy recharger.

In one case, Tomatis was called in to treat a silent order of monks at a French monastery. Although forbidden to speak, traditionally the monks sang every day -- but had given up the practice months earlier as a waste of time. They had since grown chronically tired and withdrawn. Tomatis theorized that their brains had become "discharged" by a lack of sonic stimulus and needed to be re-energized by sound and its vibrations. With five months of Tomatis therapy, most of the monks were recovered.

In the 1970s, Laurel Keyes, a Colorado music therapist, devised a therapeutic system she called "toning." The practice appears to have its roots in the ancient philosophy of Plato, who believed that certain musical tones foster upright and courageous behavior. Keyes' humming-like technique involved finding and producing the tone which feels best for the individual at any given moment. Once mastered, it supposedly improved physical and mental health.

Keyes described toning as spiritually uplifting. Neil Anderson says the humming in his novel is a metaphor for spiritual transformation. In fact, humming has had many spiritual incarnations.

For instance, the ancient Vedas, Hinduism's sacred books, emphasized using certain kinds of sounds to achieve deep meditative states, says Jean Houston, director of The Foundation for Mind Research in Pomona, N.Y., and cofounder of The Possible Society -- an organization that reasearches human potential. Similar traditions, she adds, have existed for centuries in the cultures of the Chinese, Japanese, Tibetans and the Hawaiian Kona, among others.

"There is a great tradition of humming used liturgically, sacramentally and meditatively," says the psychologist and educator. "OM, of course, is the ultimate hum sound. But these traditions have many sounds that end in 'em' and 'um.' You find it in forms of mantra . . . sounds repeated to stabilize consciousness and open it to larger reality."

The key to mantras, says Houston, is a deep humming that holds attention to a communion with God. "It's the sound of a baby cooing. It's the sound of contentment."

Ancient Egyptians, according to Houston, held that humans had five separate bodies and that humming certain frequency pitches brought the bodies together.

"Modern science also knows sound to be one of the great connectors, as it is of will, creativity, memory and emotions," says Houston. "So ancient tradition isn't too far off. Different parts of your brain are doing different things and have different functions. In deep meditation, in deep rapture, perhaps in love, many of these waves get synchronized."

She takes the connection a step further.

"Today, we are living in a planetary culture," she says. "The world is high-wired. What is it that will bring us together? Is there any way that we can begin to hum together and reweave the planetary parts?"

Bonnie Barnett and your Global Hum, where are you?

Hummmm.