It would look like a home movie except that it is split screen, this cinematic record of one of pediatrician T. Berry Brazelton's experiments on the interaction between babies and parents.

On the right side of the screen, a 3-month-old baby goes through everything he knows, smiling and fidgeting, trying to win a responsive smile from his mother. She, on the left side of the screen, stares back, stony-faced.

"She just doesn't respond," narrates Brazelton. "He can't believe it . . . Then he starts playing with his own hands, own clothing. He does what babies in hospitals do; he turns inwards. And when she leaves, he never looks up.

"This is a well-mothered baby, but this system is so critical he falls apart over a three-minute period . . . and look at the anguish on (the mother's) face."

The film stops. The house lights come up. Brazelton tells his audience (this time, at Christ Church in Alexandria), "I hope you can see how important it is. The mothers watch and say 'My God, I never knew I was that important to my baby.' "

Dr. Brazelton has a mission of sorts: He wants to convince mothers and fathers they are important to their children and that raising children is important to them. He has written three books on the subject, is associate professor of pediatrics at Harvard Medical School and does his research through the Boston Children's Hospital Medical Center, where he is chief of the Child Development Unit.

Although he does not prescribe any one answer, he does think the choices could be made easier with some help from the government.

He would, for example, like to see legislation making a six-month (maternity) leave for mothers and a three-month (paternity) leave for fathers "mandatory." The government, he says, would "require employers to hold jobs open for that length of time," and then parents could make their choice.

"Most societies now," he says, "Russia, Sweden, and China's just beginning, have come to that already. We're lagging. They've realized unless you heighten the experience and stamp it as important at the government level people will hide behind the fact they've got to get back into the marketplace. They've got to keep up on the competition and they won't pull out and learn to nurture."

He'd also like to see government "take responsibility for covering the quality of day care, having people go out and inspect and look for quality, based on minimum standards, not just safety and health, but on emotional well-being and opportunities for the child to develop. Really very much like Head Start was handled."

A third area in which Brazelton envisions government help: tax incentives to encourage employers to offer more flexible work schedules.

Brazelton calls "latchkey kids" (those who come home to an empty house) a "risk for all of us . . . really a cultural responsibility, not just the families.' "

Brazelton is well aware that the mood in Washington these days is to spend less, but "if parents begin to band together and make demands they could have a pretty big effect."

Although Brazelton, 63, still sees the mother staying home with her baby as the most ideal situation, he has graduated from the '50s myth of maternal nirvana to the realities of 1982. He knows huge numbers of women cannot afford to stay home, either financially or psychologically.

His wife Christina of the last quarter century gave up her work as an editor, saw him through the early years of his medical career, bore and raised four children, ran the house. About five years ago, she appeared with her increasingly famous husband on a television talk show in Venezuela.

"I was telling 'em about all this exciting stuff I do with babies and they turned to her and asked her what she did and she said, 'Nothing.'

"I was really depressed," says Brazelton. "I thought it was just pitiful."

He calls that moment a turning point, "that, and having three (grown) daughters who are quite into the women's movement." (The Brazeltons also have a son, 17, born when Dr. Brazelton was 46.)

Mrs. Brazelton now runs a gallery in Boston. "She's a different person," he says. "There has to be some sort of balance."

Brazelton says it is possible for that "balance" to include a fulltime job for the mother, so long as the mother makes it work: by such things as "saving up energy so when she gets home at night she can get to that baby.

"The baby will save up for the mother, save up important information for her. If the mother will keep it alive, it's there for her."

Brazelton talks about a not uncommon situation in which a toddler will be passive at a day-care center or with a sitter, then "blow up" when mother arrives in the evening.

"The care giver will say," Brazelton's voice takes on a syrupy smugness, " 'She never does that with me, dear.' But the blowup's because the baby's been saving up all day. That's important stuff, and after the blowup, the baby's the most alert, the most accessible she's been for all that eight-hour day."

It is not his intent, says Brazelton, to make mothers "feel guilty" about leaving their children, but to say, " 'Look at what you're missing.' "