Billy McGuire, a 17-year-old of better-than-average intelligence, was graduated this month from Prince George's prestigious Eleanor Roosevelt High School's science and technology center.

According to his parents and teachers, Billy worked hard, "did everything the teacher told him to" and got up a 5 most mornings to do the extra homework problems in the back of his textbooks. He scored higher than the national average on college board exams and plans to attend the University of Maryland this fall, perhaps to study computer science.

In Billy's case, however, appearances are indeed deceiving. When he was 2, doctors told John and Barbara McGuire their second child suffered from histidinemia, a rare genetic disorder in which the body is unable to produce an enzyme that is critical to normal development. One neurologist predicted that Billy would never learn to walk or talk, said his mother.

Today, the chief outward manifestations of Billy's disease are a palsied gait, thick speech and involuntary spasms of his neck and face muscles. Neither his older sister nor his younger brother has the disease, and doctors say it is not hereditary.

Billy says he feels not bitterness toward the people who still talk down to him because of the way he looks and speaks, or toward the teen-aged boys who telephone him and "say nasty things," according to his mother, or just hang up.

But Billy has been watching, reading and thinking about what is right and wrong and cruel in the world. Sometimes his feelings spill out in a rush of words.

"It gets me angry," he says. "I tell them about it sometimes. Or sometimes I just ignore them. I hate the word predjudice. It's unfair. They label people -- like religion, race, sex . . . 'handicapped.'"

Billy's mother says the effects of his harsh social experiences may prove more crippling, in the long run, than his disease.

"yi felt very depressed about it," says Barbara McGuire. "Naturally, you wish the best for your child."

After his condition was diagnosed, Billy's problem had a name but the doctors admitted they knew little about the prognosis, even less about a cure.

"No one could advise us," said his mother. "The doctors at Johns Hopkins said, 'use your own best judgment.'"

Billy's parents were determined not to institutionalize him, and to help him achieve his full potential. But his mother said she had no idea what to expect when she took Billy at age 4 unable to walk or speak, to what is now called the Ardmore Developmental Center.

In 1968 Ardmore was called Prince George's County Retarded Day Care Center. Today it is a private institution offering vocational training for handicapped adults, but then, recalled John McGuire, "It was the kind of place where you'd walk in and a 40-year-old man with the mind of a 4-year-old would run up to you and kiss you on the cheek. Sometimes after I dropped him off I'd go back to the car and cry."

But the next year, Billy was discovered by the Prince George's County public school system which, according to Billy's father, periodically reviewed records at the daycare center in search of young children who could benefit from public education programs. Though he still could not speak, the school authorities felt Billy could benefit from training at the Lincoln Special Center, now called the Glendale Special Center.

Billy has arm memories of the Lincoln center, where he finally learned to speak at age 7. It was there that he first knew he was different from the other handicapped children, some of whom were severely retarded.

"I could do more things than they could. Certain activities, like throwing the ball," he remembers.

His mother says he tried to tell her that he was like other children at a very early age.

Barbara McGuire's favorite story recalls the day Billy, at age 3, spelled the word "book" with his sister's alphabet blocks, pointed to a book and tugged at her skirt for attention. Later, at age 6, he wore a bracelet bearing the words "can't talk." His mother said one of Billy's earliest sentences was, "'I want this off now.' It was a matter of pride with him."

When he was 8, Billy left the Lincoln center and was enrolled in a special-education class at Bladensburg Elementary School. But after 3 months he insisted he could handle a regular classroom. The first thing he did there was win the spelling bee.

"It was the first contest I'd ever been in. It had special meaning. It meant I could do anything that other people could," said Billy, during an interview in his family's comfortable Cheverly home.

Billy never looked back after that first victory. His graduation from Eleanor Roosevelt, however, has brought hi a lot of "embarrassing" attention from the media.

The county school board presented him with the Outstanding Student Award of the Disabled American Veterans in a ceremony that brought tears to the eyes of school board president Jo Ann Bell.

Billy sees his graduation as the triumph of a self-made man. "No!" he shouted when asked if anyone pushed him in his studies. "I was pushing myself. It was self-instinct," he said, drawing his thick brows together in a frown.

"It's like being independent. If you intend to have a job and support yourself, you have to be independent," he said firmly.

When he was 11 and 12, during the recession of 1974-76, Billy read the newspapers and watched television news report about severe unemployment combined with inflation. He says he feared then that he "might never get money, might never get a job."

Billy kept these and other fears to himself, but his father says he was a target of abuse from some of his classmates.

"At Lincoln center he had an open, trusting face," said John McGuire, looking at a picture of Billy taken during those years. "He was sheltered. Once he left, the world started to change. It was hard to keep track of him all the time. He drew into himself in junior high school.He sort of kept his own counsel."

Once Billy stunned his father by asking for steel-toed construction shoes to wear to his seventh-grade classes.

"Apparently, some kid would grab him every day, step on his toes and rock up and down on them," said his father, who did buy him the protective shoes. "It is not going to do much for your opinion of mankind. God knows what else I never found out about."

Billy's parents say he made just one friend in high school, a star player on the school baseball team who will enter the U.S. Naval Academy at Annapolis this fall. They say he was only a good acquaintance, someone who treated Billy decently when they rode the school bus together. But his father says Billy has made his own world through reading.

"He does obscure things, like read the world almanac," said John McGuire. "A couple of years ago he memorized the five-year calendar. You'd give him a date and he'd tell you what day of the week it fell on.

"He has an egalitarian outlook toward life. It's strange. There's a lot of (published material) coming into my house. I have to assume he reads much of it," Billy's father said. The publications include Life, Look, The Economist, Fortune and computer trade magazines. "He doesn't say much," his father added, "but when he makes a comment, he goes right to the heart of something."

What does Billy think about?

"I think church is kind of boring. It's not like the house of God. All you do is stand up and sit down.Then you have to listen to a sermon on the most boring topic he (the minister) could think of.

"My father says I'm not religious because I don't go to church. But I am religious. I really like books about God," Billy continued.

"I'm not sure I'm gong to have kids. Inflation is going to eat up all our money by the year 2000. After I graduate from college I want to get a job. Then I might get married -- and move out of this town. It's the people, they're always bothering me."

Billy said when he gets to the College Park campus he may try to pursue a childhood dream -- a career in sports announcing. Why does he want to do the one thing his handicap may never let him do?

"To communicate with other people, tell them to be kind to one another."