Le Ba Son's face breaks into a smile when he describes stepping off the jet that brought him to the United States in 1981. He was alone and 15 years old.

"I thought I was okay," he recalls in halting English.

The Vietnamese teen-ager had made four unsuccessful attempts to escape from Ho Chi Minh City, where his parents had feared that he would be taken away to fight in the Vietnamese army stationed in Cambodia.

Son finally succeeded in escaping by hiding in the bottom of a boat among the boat people who reached Thailand.

The U.S. Catholic Conference subsequently took him from a refugee camp to New York. But freedom did not mean the end of his ordeal.

Until an Alexandria family became his foster family two months ago, Son moved back and forth across three states, a plight that social workers say may be typical of the odyssey in America faced by many of the 3,000 unaccompanied refugee children here.

In some cases, the children's sponsors exploit them, taking the young refugees' government welfare checks.

In other cases, government officials say, the children become disillusioned after discovering that, as Northern Virginia refugee specialist Dennis Hunt puts it, "the fantasy of life in the United States didn't work."

William Eckhof, manager of a Department of Health and Human Services program for refugee children, said that no one knows for certain how many refugee minors are in the country and what sort of care they are receiving because "It's hard to find them."

Social workers say that it is difficult to piece together what happened to Son after his arrival in New York, largely because of his reluctance to talk.

The social workers know that he first lived for three months in Brighton Beach, N.Y., with someone who had agreed to be his sponsor.

Then, for reasons that the social workers cannot discover, Son moved to Hyattsville, where he lived for six months with someone else.

From Hyattsville he moved back to New York, where he lived for a time with an acquaintance.

It was during his second stay in New York, says his foster mother, that Son was told that Arlington offered a better environment.

Acting on this advice, Son moved to the Clarendon area, which has a substantial Vietnamese community. That is where the young refugee was living when the county's social workers found him.

"He was living in a terrible place with four other people in a one-room apartment. The windows were broken out. . . he was living on noodles," said Hunt, director of a federally funded program in Falls Church that tries to find homes for refugee children.

Within a week, Hunt was able to place Son with Don and Shirley McClafferty, who live in Alexandria's Warwick Village neighborhood and have two children, Murrin, 11, and John, 15.

"We were ready to have more children in the family. . . and this seemed like an interesting alternative," said Shirley McClafferty, who works as a secretary in a law firm.

Today, the 17-year-old refugee's life with the McClaffertys appears much like those of other suburban teen-agers.

Son listens to rock music, watches television, rides his moped and works at a McDonald's restaurant.

But he also carries with him a burden of memories and a reluctance to talk about the life he left behind.

"Sometimes Son is overwhelmed by the finality of his situation because he knows that he can never go home," says Shirley McClafferty.

"I don't know how he survived," she says.

What Son says he likes most about America is what he calls his "second family."

A short, slim youth, he will not speak with strangers about his past and the McClaffertys say that he is just beginning to talk to them openly.

"He knows that if he goes back, he'll be killed. He has no hope that his parents will ever be allowed to leave. . . . He's more realistic than some of us would be in his situation," said Dan McClafferty, who manages a trucking company.

Hunt says that Virginia gives $203 a month to refugee children, with the sole stipulation that they have some adult supervision.

In the Northern Virginia area, the seven families who have accepted refugee children since the program began in March also are given special counseling and guidance to help them meet the children's needs.

In addition, translators can be provided to help communications between the youngsters and their new families.

"Sometimes, on the surface, they are adjusting beautifully. . . ," Hunt said. "We have several straight A students. . . but they still have nightmares and wake up screaming."

Shirley McClafferty said that, although Son no longer has the nightmares he had after his arrival in the country, he still mentions a fear that the Communists will find him and take him away.

"I don't think it's ever very far away from him," she said.