It's the flash, that rush of recognition when you know you've gotten through to the child lost somewhere inside the perfect frame. And then the eyes glaze over and the boy is gone. Just a flash -- but if it weren't for the flashes, Beverly Sills wouldn't know her child.

On stage she is Cleopatra, Elizabeth I, Rosalinda -- known throughout the world as a prima donna and general director of the New York City Opera. At home, she is the mother of two handicapped children who were born with birth defects.

Her daughter, Muffy, 28, who is deaf, is an artist and lives a full, rich life. Her son, Bucky, 26, is severely autistic, retarded and epileptic. A handsome boy with brown eyes and brown hair, he cannot speak.

Sills tells the story about one of the flashes. It's about her mole. When she visited Bucky at a special institute in New Jersey, all his eye could focus on was the mole on her chin. He would sit in her lap and touch the mole.

Then seven years ago, when Bucky was about 19, a little cancer was discovered in the mole and it was removed.

After the bandage was off and she went to visit him, "he kept stroking my chin looking for the mole," Sills recalled. "He was crying and crying and I did not know what to do."

They stopped at a drugstore and she bought a black eyebrow pencil. Then she rew a mole on her chin. Immediately the boy stopped crying and started to laugh -- eureka! He had found his mother again. He kept laughing and began smearing the black dot all over her jaw.

"It was so odd, but in some way in his mind, that was Mama," said Sills in an interview last week.

A moment of awareness . . . the flash . . . the triumph for mother and child. No one who hasn't had a handicapped child can understand what it's like. "Much too often, when I talk about my children, well-meaning people, trying to express their sympathy, respond: 'I know how you feel.' They do not know how I feel," Sills said at the National Press Club last week. One time she went to a party in Seattle for 12 children who had among them more than 100 different birth defects. "The mothers of those children do know how I feel. And I know how they feel," she said.

That hard-earned knowledge is one of the reasons Sills is chairman of the March of Dimes 50th Anniversary and its campaign to get more funds for research to prevent birth defects, to help scientists chart the billions of bits that make up the human genetic code in the hopes of repairing or replacing defective genes.

But asking Sills about the details of DNA, she quipped, "is like asking Madonna to sing 'La Traviata.' "

What she does know are the statistics. Every 18 minutes a baby is born in the United States with a birth defect. The cost of caring for infants in special nursery intensive care units exceeds $2 billion a year, and because birth defects usually last a lifetime, the total annual cost is many times that figure.

"The more we learn about inherited disease, the more we know that nobody is safe from birth defects," Sills told the Press Club audience. ::

She was born Belle Silverman and grew up in Brooklyn with the nickname "Bubbles," the daughter of immigrants in a family where the brothers became doctors and the girls were to be teachers. But she was different. By the age of 7, she knew she wanted to sing opera and her idol was Lily Pons.

In 1932, she began singing on the "Uncle Bob's Rainbow House" radio program. Then she became a weekly guest on Major Bowes "Amateur Hour." In 1955 she made her debut with the New York City Opera. The next year she married journalist Peter Greenough, moved to Boston and became stepmother to his three daughters -- one of whom is retarded.

Then Muffy and Bucky were born and there they were, living in Boston with five children. Her husband gave her a present: 52 round-trip shuttle air fares to New York to take singing lessons and see her mother. "It was a total escape," she said. "My mother is a giggler, a real upper: nothing is wrong, God is with you -- everything is all pink and shiny. I was Mama's girl for a day."

As a superstar for 30 years who has performed in every major international opera house, she is always asked: how did you balance your career with your family? She laughs: "My husband says I relax by walking on the ceiling." And balance? "In the early days I cannot honestly say we balanced things well," Sills said.

Yet her career blossomed. She could pick and choose her roles. She'd take the whole family when she was on tour. But always there was worry and guilt. "Somebody pays a price with a career like this," she said. "My daughter Muffy paid the price."

But her husband was there and supportive. When Muffy graduated from high school, she said to her father: "I think I should tear the diploma in half because half of it belongs to you."

Being deaf, Muffy can never hear her mother sing. But being deaf, she has given her mother a special sense of triumph. The first utterance of "Mama" from a hearing child is merely exciting, cause for a phone call to the grandparents. But the first words from a child like Muffy, after all that you go through: "It is such a moment of triumph not only for the baby but for you," said Sills. "A normal child doesn't give you that." ::

Sills didn't really take a full-time regular job until she was 51 and the children were grown. She began her second career as director of the New York City Opera in the midst of union negotiations. It was not an easy beginning. But she knew voices, she knew repertoire, she didn't have a temper and in many ways the problems of managing a large company seemed easy after raising her children.

"When you've already lived through the worst day of your life, very little fazes you," she said. "You put everything in proportion."

That sense of proportion has placed her at the forefront of the battle against birth defects. Since 1971, she and her husband have worked with the March of Dimes and talked openly about their children. Greenough is a member of the March of Dimes National Board of Trustees. Until last year, Sills was chairman of the annual Mothers' March.

Always it comes back to the mothers, she said, and she has spent many hours sharing the despair -- and the flashes -- with mothers of handicapped children. "Many men can't deal with it," said Sills. "The fathers have an escape. They have to continue with their jobs."

What all families share is the fatigue that comes from taking care of a handicapped child -- a kind of lead blanket that wraps around all members in the family until they are so drained they feel they can no longer function.

Even now when Sills and her husband come home from a day with Bucky, "Peter cannot speak," said Sills. "We are so drained."

During summer visits, they like to go to the state park. One time, just after Labor Day, she and Bucky went for a walk in the park. Suddenly, as they started to go down the path, he put his arm around her shoulder. Her husband watched from behind. Flash. Later, she said, her husband told her that "for a moment, the way he had his arms around me, we could have been any mother and son."