"Willie" was only 4 months old, but his face wore a worried expression out of harmony with his age. His mother smiled and hugged him close, crooning softly. But he arched his back, held himself away from her, and stared stubbornly over his shoulder in the opposite direction.

At 4 months, when a baby should be in love with the world, Willie refused to look at any human face.

"The baby is honest," Dr. Stanley Greenspan said as he watched the videotape of the infant and his mother. "He'll carry the history with him. He won't perform for the camera."

Willie was perhaps the most troubling of the 100 "high-risk" infants being studied at the mental health research center in Adelphi, Md., where Greenspan and other psychiatrists are delving into the core of the human personality. Their goal: to learn whether babies whose early development is being derailed by a bad relationship with their parents can be identified, and to try to prevent permanent damage to the infants' intellect and emotions.

Psychiatrists approach babies with methods very different from the couchside analysis and dream interpretation that have come to symbolize orthodox psychotherapy for adults. Yet, Greenspan and other specialists say that a baby only a few months old can have mental problems just as real as an adult's, and potentially more crippling. Since babies can't talk, the specialists watch for warning signs such as failure to make eye contact, lack of interest in the world, refusal to eat, constant crying or sleeping, even repeated vomiting. Such symptoms have many causes -- but in some babies, they are evidence of a dangerously disturbed parent-infant relationship.

Therapists working in experimental programs such as Greenspan's treat each infant with tactics tailored to the baby's particular problem, level of development and family environment. Therapy can include adding or subtracting sensory stimuli, exercising overly tense muscles, providing affection or communication that is missing at home, and counseling parents about their infant and their own reactions to him.

What happened to Willie and his mother, as recounted by Greenspan and glimpsed in videotapes that chronicled their progress over the following year, testified to the promise of this new branch of science. The success of experimental therapy for them, and for other vulnerable babies and mothers, could influence future efforts to prevent child abuse, learning disorders and juvenile delinquency. As health planners consider the costs and benefits of psychiatry, some predict that early infancy may turn out to be one period when careful evaluation and counseling -- whether by a doctor, nurse, psychologist or social worker -- can make a difference. Others worry that the cost may be too high, or that babies or parents might suffer from being labeled as problems.

The U.S. surgeon general, child psychiatrist Julius Richmond, believes research such as Greenspan's helps doctors learn how to identify infants who face the greatest risk of intellectual and emotional damage. He agreed that for the most disturbed, intensive early therapy may prevent problems later. But he said that might take years to find out.

"One needs to be very cautious about interpreting experiences in the early weeks and months of life as being 'critical,'" he said. "I would not suggest that it's ever too late."

Beyond reaching babies who need their help, Greenspan and other specialists hope to unify knowledge about babies' physical, mental and emotional growth, about how each baby differs from others even at birth, and about how his interactions with his parents can nourish -- or stunt -- his unfolding personality.

Willie's mother came to the mental health center before his birth. Workers at the clinic, a research outpost of the National Institute of Mental Health, had let Prince George's County nurses and social workers know that they were looking for troubled mothers: those with a history of child abuse or neglect or severe mental illness, or children with serious emotional problems. Willie's mother had been abandoned as a baby and beaten as a child. Now she was pregnant. She arrived at the clinic uncertain what she was looking for, and ready to trust no one.

A social worker on Greenspan's nine-member staff began seeing her before the baby's birth, and a psychologist and a nurse trained to work with infants examined Willie at birth and one month later. His muscles were more tense at birth than are most babies' and he tended to arch his back and turn his head. To his mother, his rigidity could mean only one thing: her baby was rejecting her. She became nervous, then angry. When Willie cried, she ignored him -- sometimes for hours.

By one month of age, Greenspan recalled, Willie clearly was looking away from his mother."It was quite a worrisome situation. The mother was suspicious, guarded and paranoid, and here little Willie was not a baby who looked at you, 'trusted' you."

From the beginning, Greenspan's team concentrated not just on the baby or the mother, but on how they responded to each other. They took into account the growing recognition that babies are people, capable from birth of observing the world and reacting to it.

"It started with people realizing that infants were a lot more complicated than anybody had given them credit for, and were having a lot more effect on everybody around them," said Dr. T. Berry Brazelton, a Harvard Medical School pediatrics professor who is another pioneer in the field. "It was kind of a revulsion from blaming the parents for everything."

In Willie's case, the problem began when his mother misinterpreted behavior that simply reflected the level of development of his nervous system. His arched back and tense limbs did not mean that he was rejecting her, but that his brain was still too immature to control his muscles.

Babies are born, according to Greenspan, with brains that are still growing rapidly and that each day form new connections between millions of nerve cells. Many nerves are not yet coated with myelin, a protective sheath that speeds the electrical impulses that make us feel, think and move. Just as newborns are not able to talk or sit up, it also takes time for their nerves to mature so that they can control their muscle tone and screen stimuli from the outside world. This process continues apace for the first two years of life, and is not completed until adolescence.

While a "normally competent" newborn baby may become startled and cry a few times if he hears a rattle, he tunes the noise out if it continues.But Greenspan said some babies are not able to do this.

Despite the popular emphasis on "stimulating" babies with noise, touch and color, "some babies need just the opposite of stimulation," he said. Ordinary noise levels, bright light, or even being touched on the legs or buttocks, can make them cry constantly and tense their muscles. "They look like they're in a panic state, Greenspan said.

"Most grow out of it. It seems a temporary inability to establish a threshold. But for mothers for whom that wasn't recognized, there could be a severe problem in the early relationship."

Greenspan's treatment of Willie and his mother began with a thorough evaluation of both. Besides doing a physical examination that included tests of the baby's nervous system and his IQ, the clinic staff videotaped Willie and his mother and "scored" how the two were getting along.

Psychiatrists who specialize in the study of infants divide the early months of a baby's life into overlapping stages. While the doctors differ on details, they agree on the basic sequence. A baby approaches each stage with his own physical resources and personality, and at each stage his progress is influenced by his environment -- chiefly, the response of his parents.

For instance, Greenspan said, the first stage, starting at birth, requires the baby to learn self-regulation: eating and sleeping in cycles, learning to screen out a sensory barrage so that at times he can be alert without crying. How quickly he progresses may depend on whether he was born prematurely, how healthy and relaxed his mother was during pregnancy, and how she handles him in the early weeks.

Many babies, he said, can be calmed by a soft, rhythmic voice or by being rocked gently in rhythm with the mother's heartbeat or their own. But a mother who responds to crying by talking loudly, or roughly bouncing the infant or jabbing a bottle in his mouth can make it harder for him to calm down.

Willie's rigidity and hypersensitivity to stimulation meant that when he was not sleeping, he was crying. His mother made matters worse by ignoring his tears. Both were ill prepared for what Greenspan considers the second stage, a period lasting from about one to six months of age, when most babies become fascinated with the world, and especially with the person who cares for them.

One of Greenspan's videotapes shows a normal baby during this stage. As his mother talks softly to him, his eyes are fastened on her face, and he wears a look of utter fulfilment. "This is the epitome of what we all yearn for in life, to have someone look at us that way," Greenspan said.

That is why the tape of Willie at 4 months frightened the psychologists. His refusal to look at his mother was the most abnormal act a baby his age is capable of.

The staff responded by assigning one therapist to Willie's mother and another to Willie. The infant specialist -- a pediatric nurse trained to work with babies -- devised a game. Since Willie ignored real faces, she drew a face on a piece of cardboard and got him to watch that. Then she would lower the cardboard face to reveal her own.

"That, he found interesting," Greenspan recalled. Willie played the game tirelessly, and in a few weeks began to prefer a human face to the cardboard one.

While the specialist saw Willie three or four times a week -- playing the game, rocking him, gently exercising his muscles to relax them -- his mother's therapist tried to talk with her two hours a week about her own feelings. But his mother was moody and unpredictable.Some days, she wouldn't let the therapist into her house. It was several months before she would play the face game with Willie herself.

On videotape made when Willie was 8 months old, he looked much more normal.

He had progressed successfully into the stage, lasting from roughly 3 to 10 months of age, when a baby starts learning to communicate with the outside world. He could bang a bell gleefully, knowing the action would produce a noise. Although his movements were sometimes jerky, his control of his muscles had improved dramatically. Most important, he had learned who his mother was.

That was an important landmark. By 8 months, most babies develop what is called "stranger anxiety": they distrust people they don't know. They can tell one individual from another, and they learn that different people react differently to their actions.

But Willie's mother was lagging.In one part of the tape, as Willie played with a therapist, he kept glancing at his mother and smiling. Once he reached over and touched her knee. But she sat smoking and staring sullenly away from him. When he reached out, she withdrew her hand.

At 8 months, "he was the more persevering," Greenspan said. "He would not tune out or turn away when the mother would withdraw."

But the team's approach seemed to be succeeding. The mother's therapist had helped her find a new apartment, and as they drove around the neighborhood, she had at last begun to talk about her sense of isolation. She could cope with her own moodiness more easily and take care of Willie even when she felt like tuning him out. Greenspan and his staff were encouraged.

They took advantage of her new receptiveness to involve her as much as possible in Willie's sessions, and her own therapist talked with her about three times a week. It paid off: The videotape done when Willie was 13 months old showed a heartening change. This time, Willie's mother looked happy and interested, helping him play with wooden pegs and talking to him on a toy telephone.

"At this point, they met each other," Greenspan said. "The nice thing was that Willie was ready to meet her."

Without the help of the infant specialist, Greenspan believes Willie might not have been ready. "The youngster at each stage has to be met with those environmental nutrients needed for the developmental task," he said. When a mother with severe mental problems has a new baby, "you can't take two or three years to do intensive psycho-therapy. You want to do something more quickly." y

Greenspan acknowledged that the treatment given to Willie and his mother would be expensive if they had had to pay for it. He said that the therapists' time alone, in a program as intensive as this one, would cost at least $5,000 a year for each family. And for most mothers and babies, it would be overkill. Yet, when a parental relationship is extremely abnormal, he believes it may be cheaper in the long run and more effective to offer psychiatric help soon after a baby's birth than to wait for a learning disorder or emotional problem to surface years later.

Brazelton, the Harvard professor whose research in infant psychiatry grew out of his experience as a pediatrician, believes that programs such as Greenspan's are too expensive except for extreme cases. But he said he is impressed with the long-term benefits of offering even minimal instruction and counseling to mothers who are very young, disadvantaged, or have little knowledge of babies and parenthood.

"The professional question, in terms of social policy . . . is, are these the kinds of programs we need to have? Greenspan said. "My own feeling is, there's no choice. Because if you don't work with Willie and his mother now, you'll wind up working with Willie and his mother when he's in school, using much more resources, with much less chance of a positive outcome."