Four years ago, the first winter-depressed patient at the National Institute of Mental Health wistfully suggested that she "should have been born a bear" so she could sleep the winter through. Since then, the study of people whose spirits bloom with the crocuses and fade with the autumn leaves has captured the attention of the international psychiatric community.

This is in part because the phenomenon is vastly more common than researchers initially believed. Also, in most cases of the syndrome, now called SAD -- for seasonal affective disorder -- the gloomy winter moods can be quickly and completely dispelled with light.

Dr. Norman Rosenthal, chief of outpatient studies of the NIMH Clinical Psychobiology Branch and a pioneer in the identification and initial studies of the syndrome, has now seen some 170 patients and treated more than 60 with lights, with a better than 80 percent response.

His findings that the bright lights, which simulate the full spectrum of normal daylight, can reverse the winter depression (presumably by artificially lengthening the short winter day) have been replicated in studies in Switzerland, Alaska and Oregon. Many of the investigators will be comparing notes this week at a symposium in Philadelphia. Although not all the researchers have used the lights in the same way, and may explain their success with different hypotheses, they all agree that the syndrome exists.

It appears most commonly in women, although men are also affected. All the researchers agreed that bright lights can reverse the depression, the sleepiness and other symptoms that otherwise would not lift, typically, until the days begin to lengthen in the spring.

Now Rosenthal has discovered the apparent existence of the syndrome in children, and one major study to validate this finding is getting underway at the University of Minnesota. Rosenthal and the NIMH team will continue their studies of adults.

Typically the adult "seasonal," as the researchers call these people, begins to "slow down" in the autumn. She is consumed by lethargy and food cravings (especially for carbohydrates. She never gets enough sleep and will complain, even after 12 hours a night. One patient after another talks about decreased sex drive, trouble with interpersonal relations, trouble with their jobs. They are depressed, often deeply, and view life with pessimism, often despair.

And year after year now, since 1981, Rosenthal and his colleagues at NIMH and elsewhere are seeing happy, optimistic, often highly creative, energetic and articulate people emerge after only a few hours of bright light treatment, usually two to four days after therapy begins. (Rosenthal emphasizes that treatment of depression is not a do-it-yourself project, and light therapy should be used only after careful diagnosis and under a doctor's care. It can sometimes have side effects, and its withdrawal can cause a patient to "crash" back into depression.)

Some of the patients treated successfully last year mentioned to Rosenthal that they were seeing some of their own winter symptoms reflected in their children. As a result, he says, "we treated six kids, five of whom had clear improvements with light."

"It is especially cruel for children," says Rosenthal. "Because it happens so early in their lives, they frequently do not identify it as coming from within themselves and instead they see the world as having turned unfair and cruel. The teacher is demanding too much. Parental expectations are unfair. These are the frequent complaints, and if you don't think of the seasonal angle on it, you might not pick up on it."

Of the five youngsters who responded to light, says Rosenthal, one was a champion swimmer whose times had always, inexplicably, dropped in the winter. Last winter, after the light treatment, his swimming times actually improved. Another child, a 13-year-old boy, "made the honor role for the first winter of his life."

Dr. William A. Sonis, pediatrician and child psychiatrist at the University of Minnesota in Minneapolis, is readying a larger study on SAD children. Sonis was a fellow at the National Institutes of Health, and his interest in circadian rhythms -- the body's natural clock -- drew him to Rosenthal's work, even though he was in a different institute. The kinds of seasonal variations involved in SAD are among the biological rhythms that seem to govern the way our bodies work -- why we sleep when we do, eat what and when we do, feel how we do at any given moment.

Now Sonis and his colleagues at the University of Minnesota are planning to recruit depressed children (between the ages of 6 and 18), treat them all with the lights and see who responds to the treatment and who does not. Then, through rating scales and interviews, they will try to put together a profile of a SAD child.

"The word is beginning to get around," says Sonis. "Part of the whole problem is that it is not recognized in kids. It is mistaken for problems of school adjustment or growing pains. People will say, 'Oh, it'll go away. He gets like this every year.' And of course it does go away, but they don't recognize that it doesn't have to be that way."

Although the NIMH researchers have used the bright lights for up to six hours a day -- three hours in the morning and three in the evening -- subsequent studies are suggesting that two hours a day, in either morning or evening, may be sufficient.

Indeed, says Sonis, there is the possibility that the seasonal mood variations "may be some kind of general pattern that runs in all humans and is just expressed severely in some," so that lighting may have effects even on people who notice no special seasonal changes.

Because of that, and because of some Soviet literature in which use of ultraviolet light during the long Russian winter apparently improved school performance, Sonis and his colleagues are planning another experiment. They hope to install full-spectrum fluorescent lights in a Minneapolis school room. "We might be able to get some of that benefit with these lights without exposing the children to the potential risks of ultraviolet light," Sonis said.

The Minnesota project is almost entirely concerned with treatment, but the NIMH scientists are also concerned with the mechanism of the phenomenon. Because SAD appeared closely related to the body's production of the hormone melatonin, which is produced only at night, and because melatonin plays a major role in governing the seasonal behavior of many animals, the researchers hypothesized that blocking melatonin synthesis would lift the depression.

The studies last year failed to fully support the hypothesis, indicating that something in addition to melatonin was at work. Rosenthal hopes this winter to recruit volunteer SAD victims (ages 16 and older) who will receive the light treatment and also participate in some studies of the neurotransmitter serotonin and how it may be implicated in SAD. Serotonin is found in all parts of the brain and has been linked to sleep cycles, carbohydrate craving, appetite satiety, feelings of contentment and pain relief, among other things. Resources

Seasonality Study (for those aged 16 and older), Clinical Psychobiology Branch, National Institute of Mental Health, Building 10, Room 4S239, National Institutes of Health, Bethesda, Md. 20892. Phone: 301-496-2141.

SAD Child Study (for ages 6 to 18). Dr. William A. Sonis, Box 95 Mayo, 420 Delaware St. SE, Minneapolis, Minn. 55455. Phone: 612-373-8871.

Duro-Test Corp. for Vitalite lamps, full-spectrum lights used in most SAD studies and for information on industry-sponsored studies. 2321 Kennedy Blvd. North Bergen, N.J. 07047.