No one knows for sure how it happened.

The Maryland State Police think that Virginia Bucia turned around in the driver's seat to reprimand the kids, and thus took her eyes off the road. Regardless, at 2:15 p.m. on Saturday afternoon, June 19, 1982, her car crossed the center line of a rural two-lane road in Prince George's County and plowed head-on into an oncoming garbage truck.

Although the truck and the two men in it were unharmed, the Bucia car burst into flames. Virginia Bucia, her 13-year-old daughter Christina and her 6-year-old daughter Carolyn were killed. So was a 13-year-old friend of Christina's.

But 9-year-old Caryn Bucia survived.

She was thrown into the well of the front passenger seat by the impact of the crash. By sheer luck, she was insulated from the worst of the flames for about two minutes--long enough for a brave passerby to reach into the smashed car and lift her out. Severely burned over 60 percent of her body, Caryn was flown by State Police helicopter to Children's Hospital.

Doctors there didn't give her much of a chance at first. Her vital signs were poor. Her back, scalp and face were severely burned. The burns on her hands were so serious that doctors doubted that she'd ever be able to use them normally again.

But Caryn Bucia will go home to Waldorf, Md., later this month, after 14 operations and six months at Children's. Although two of her fingers have been amputated, and although she must undergo treatments for her burns three times a day, perhaps for the rest of her life, Caryn Bucia will return to school in a couple of weeks. "The guts of this kid, it's just incredible," says her father, Walter.

But Caryn Bucia's recovery has also been Walter Bucia's.

Children's Hospital mends young bodies every day of the year, and the staff has done a first-class job on Caryn's. But a Children's social worker named Mary Berlin has worked just as hard to help mend a distraught father.

The logic is this: A seriously injured child like Caryn will need a rock for a father, for the next few hours and the next few years. So it's in Caryn's medical interest for Walter Bucia to receive extensive help from hospital social workers.

Walter Bucia has received that help, without charge, and Walter Bucia is a believer.

"I am a much better person than I have ever been," he said the other day, over coffee in the hospital's cafeteria. "But I never would have made it without Mary. I wouldn't have had a chance."

In her first-floor office at the hospital, Mary Berlin counseled Walter Bucia every day--from July, when Caryn was well enough to be transferred out of the Children's intensive care unit, until December, when doctors allowed Caryn to go home for a few days around Christmas.

"There were times he just sat here and wept for hours," Berlin recalls. The Bucias had been separated for three years, and "he felt terribly guilty about the accident. He wished he had been in the car, because he thought it might not have happened if he had been. And he was withdrawing from his friends, wasn't sleeping, wasn't eating.

"So what I did is what we always try to do here--give the parent a safe and acceptable place to vent his feelings. I think the worst thing in the world would be not to talk about it, and for the hospital not to give the parent a way to talk about it.

"This is probably one of the most horrible tragedies ever to come to Children's Hospital," said Berlin. "I was very worried about Walter. I still think he has a long way to go . . . . It's going to take years.

"But I think he's a lot better, even though I think he's still depressed. Walter is an incredibly strong man. Considering everything he's been through, he's held up better than most."

The Bucia case gladdens hearts among the 41 professionals in Mary Berlin's office, because it proves that social workers can make a significant difference.

"What annoys us is that people have a stereotype of social workers as welfare workers," says Berlin. "You know, 'Just give me bus fare.'

"But in medical social work, the bulk of the time is spent on dealing with the emotional aspect of the situation. We think that a parent like Walter needs to deal with his feelings, that that'll make him a better father for Caryn."

But even after six months of daily sessions with Mary Berlin, "it's hard, it's still very hard," says Walter Bucia, who is a 40-year-old butcher for the Bay State Beef Company.

"Christmas was very, very difficult. You could tell by the look on Caryn's face that she missed her mother and her sisters. There was nobody for her to play with.

"And I wasn't much better. Ever since it happened, I keep thinking they're all on a trip somewhere, that they'll be back soon . . . .

"Caryn cries a lot. She misses them all. She calls out their names. It's rough to listen to.

"But we've become inseparable. I've been here at the hospital every day, for hours. I just love little Caryn so much. Hey, she's all I got left now."

Walter Bucia admits that he has been surprised by how much time and effort Mary Berlin has devoted to him. "I figured, 'Why would parents get all this attention?' " he says. "I figured Caryn was the one who needed the help.

"But Mary made me understand that I'd have to be there for Caryn for many years. And that's made me a better person. I can see now that things are working out the way Mary said they would."

Caryn Bucia faces dozens more operations over the next few years. She will need extensive physical therapy. She will need to learn to deflect the gazes of people who may never have seen a severely burned person before.

But the outlook is hopeful, if an incident from Christmas week is any indication.

Walter and Caryn were shopping at a crowded mall near their home. As they peered into windows, they kept noticing that other shoppers were staring at Caryn.

"I was getting mad, and I was about to say something to one of them," Walter Bucia recalls, "when all of a sudden Caryn says to me, 'Daddy, I'll explain it to them if you want.' "

Of course, Daddy wishes he would never have to explain. But Caryn's strength helps, and so does Mary Berlin's advice.

" . . . You have to be strong," Walter Bucia says. "You have to learn to shake it off, to explain it. And now I can, for Caryn."