The light was just coming up behind Salt Pond as Laura Frankl wriggled out of her sleeping bag, shook out her boots and made her way through the shoulder-high grass.

Concealing herself in a natural blind near the water's edge, she remained quiet and motionless for the next hour. Suddenly she raised her field glasses and nudged her companion. "There," she whispered.

Scarcely 150 yards away, to wild monkeys had emerged from the dense growth of Whaleback Hill and were leading their troop across the sandbar spanning the pond to their feeding grounds. Two playful juveniles tumbled over each other, silhouetted against the gleaming water. A venerable male who had lingered to nibble an acacia thorn bush now followed, standing up on his hindlegs to look back every so often. A fifth brought up the rear.

It was a magic moment for Frnakl, an 18-year-old sophomore in biology from Occidental College in Los Angeles, whose expedition until now had caught only glimpses of these elusive animals.

She is one of about 30 U.S. students and scientists who were on the island last summer, attracted by the prospect of seeing and studying these close relatives of man in the wild, at what locals call "the monkey farm.".tQuite possibly the most unusual research facility in the world, the Behavioral Sciences Foundation is headquartered at Estridge, an old plantation just 16 miles from where Frankl spotted her monkeys. It coordinates a host of projects in psychiatry, anthoropology and archeology, and uses the monkey to study such human concersn as aggression, stress and anxiety, leadership, sex differences, depression, drug addiction and brain damage.

One morning at the monkey farm, for example, Yale University psychiatrist Gene Redmond was already bent over an anesthetized animal. He wanted to remove five monkey brains for analysis that day, and the lab, which is not air conditioned, already was sweltering.

Outside, from a rickety observation tower in the trees, University of California, Davis, anthropology student Janet Franklin looked down on a troop of 33 monkeys, recording their behavior on a long score sheet.

At the edge of the southeast peninsula's remote Great Salt Pond, University of California, Los Angeles, graduate student archelogist Doug Armstrong, 23, and 17-year-old Ralph Black of Bethesda picked up the first of the numerous fragments of pottery, shell and rock tools - 4,000 years old, perhaps - they'd find that day in this uninhabited area of scrub and savanna.

And Jeff Lannery, director of a primatology summer school program at Estridge, had long finished taking monkey blood samples and was now talking with UCLA psychiatrist Frank Ervin, the man behind all this activity.

The laboratory is housed in the former slave quarters and outdoor kitchen - a whitewashed stone building with red shutters and a corrugated metal roof-of the plantation. Ants scurry across the wooden work tables.

The electric current is such that the refrigerated centrifuge can either refrigerate or centrifuge but not both - so specimens are first cooled, then the compressore motor is turned off and the centrifuge is switched on.

Frozen monkeys and ice cream share space in the noisy freezer (even though it's clearly marked "no food") across the way in the old Great House.

The water often does not run. And the heat - it is unbearbaly humid and sometimes into the high 90s by midmorning - dictates that the sweaty scientists perform their delicate experimental surgery stripped to the waist.

But the primitiveness of the setting is matched by the excitement of those who come here to work, lured by the abundance of an animal the locals consider an agricultural pest - the green monkey or vervet, known scientifically as Cercopithecus aethips sabqeus. This is a species of Old World monkey millions of years closer to man than the New World variety and found on this continent only on the Caribbean Islands of St. Kitts, Nevis and Barbados.

Today there is a monkey shortage elsewhere, but there are an estimated 30,000 vervets on the 68-square-mile island, 150 of them in captivity at Estridge. Some are trapped and sold to make polio vacine; others have been sent to the Sepulveda VA Hospital at Los Angeles and to Mexico and Cuba to establish troops of monkeys there.

The island provides a cheap and plentiful supply of research subjects closely related to man and with similar genetic variability. And it offers scientists the opportunity to observe them is social groups either at close range in two large enclosures at Estridge, or in the wild in three very different environments - the tropical rain forest of Mt. Misery, a volcanic crater; the ravines bordering the sugar cane fields; and the savanna and slopes of the southeast peninsula.

Some of the research centers on how animals develop normally - for example, the differences in how young males and females play and whether those differences have anything to do with their role as adults. These animals are only watched, not interfered with or experimented on in any way.

A second type of research at Estridge is assessing the effects - on groups of normal animals - of brain-altering drugs or environmental changes like crowding or separation. And a third type of study consists of damaging some animals - making them "crazy" or violent, for example-and then trying to find ways of reversing that damage. A small percentage of the animals must be killed-the scientists call it "sacrificing"-to gain direct knowledge of what is happening in the brain.

The animals are usually studied in groups, an aspect largely ignored in biological research, even though a monkey-or a person-may react differently to a drug or even brain damage in isolation than in a social situation.

The consequences of specific brain damage, for example, differ, depending on the animal's social role. Scientific director Mike Raleigh, also of UCLA, and Dieter Steklis of Rutgers did identical brain surgery on nine vervets in a group of 21 they'd been watching carefully for five months. They removed a tiny piece of tissue from a part of the frontal cortex thought to be associated with emotion and mood, then put the monkeys back with the troop and watched them for the next six months.

All of the brain-damaged animals became less aggressive, huddled with a new set of friends and spent more time alone-as expected. But how much and in what ways they were changed depended largely on their age and sex and rank and how the other monkeys reacted to them.

The adult males' success at one-to-one fighting dropped, limiting their access to females, food and shelter. The females quit grooming and huddling and no longer came to their sisters' aid during fights. The young played less. Young females lost interest in taking care of the infants.

Formerly high-ranking males were devastated if a normal male challenged them, but started getting better at sex and grooming and fighting if the rival was removed for a week or so. Changing the environment didn't help the demaged females much.

The normal monkeys either ignored their brain-damaged brothers or continually harassed them, depending on whether they'd been competitors before. And they often compensated for the damaged monkeys' deficits, say, by more grooming of a neglected infant.

Ervin and his colleagues have methodically watched their captives for four years now and feel they can describe with confidence how the troop functions: who does what to whom and how frequently and when.

Now they are in a position to either make physical changes in the animals (via drugs or surgery) and see what changes in behavior result, or manipulate the social setting and measure any resulting biological changes - in hormones and other substances in the blood and brain.

One recent project, for example, involved raising and lowering serotonin levels, a brain chemical implicated in sleep and sex behaviors and certain kinds of depression. Raleigh, Ervin and Flannery administered drugs to 45 animals, causing them to make more or less serotonin, and looked at the behavioral consequences. In general, the animals with elevated serotonin were mellower, quieter, friendler; those with lowered serotonin became more irritable.

Now the team plans to do just the opposite: to manipulate behavior-say, by separating juveniles who have become attached to each other through playing and growing up together, thus creating a sort of experimental "depression"-and then measure any changes in brain chemicals.

What happens in a monkey may not necessarily happen in man. But because these St. Kitts monkeys are, except for the great apes, our nearest kin, the result of these kinds of studies are bound to be more relevant to human problems than behavioral studies based on rats or mice, Ervin says.

At 52, he is one of the United States' most renowned electro-physiologists and an expert on violence and the brain.

Much of the research behind this surprising report of an abnormal peptide found in the blood of schizophrenic patients last year was carried out at the monkey farm. (The substance, isolated from waste fluid saved from schizophrenic patients undergoing experimental kidney dialysis, was injected into monkeys. At high doses it caused convulsions and death: at lower levels it caused convulsive patterns in brain wave tracings, indicating that it was exciting the brain's limbic system, the region thought to be involved in emotional disturbances). CAPTION: Picture, A Mandrill monkey in repose, by UPI.