At an air show in 1956, a black youngster from Southeast Washington stood on the concrete apron of Andrews Air Force base, craning his neck and shielding his eyes to watch jets streak into the sky.

Frederick Drew Gregory's dream, like that of a million other 15-year-olds, was to fly. Having not yet heard segregation's implicit message that such aspirations were not for him, he walked up to one of the pilots and asked: "How can I become a pilot just like you?"

With that question, Gregory started on a course that has brought him to the eve of a flight at the helm of the space shuttle Challenger, scheduled to lift off tomorrow.

Gregory will become the third black American in space, and the first black astronaut to fly a spacecraft in the 24 years of manned space flight.

"I just thank God I had a marvelous family and an opportunity to do this," Gregory, an Air Force colonel and Anacostia High School graduate, said recently. "I'm lucky to be me."

Unassuming and low-key, Gregory, 44, is a man who appears comfortable with himself, his career and his life choices.

In the vastness of Johnson Space Center's Building 9A, where Gregory has trained for the mission, wingless plywood and sheet-rock mock-ups of the shuttle lie open for tests and training. NASA technicians hardly noticed Gregory as he strolled up to one of the models and climbed inside with a child's eagerness and ease.

Wearing gray cords, a polo shirt and a weathered, brown leather jacket, he squeezed behind the array of instruments on the shuttle's flight deck, saying he likes the privacy of the small space.

"I'm doing exactly what I always wanted to do, and that is to fly and do something that's a little different with my life," said Gregory. Married to his high school sweetheart, the former Barbara Archer, and the father of two children, he lives with his family on a cul-de-sac in suburban Clear Lake, 10 minutes from the space center. "I am very happy I have been able to progress this way . . . . I don't have a big head or anything."

Gregory, product of two prominent Washington black families, comes from a long line of achievers that included educators, ministers, lawyers, engineers, scientists, politicians and even an aviator.

His most famous relative was on his mother's side of the family -- his uncle Charles R. Drew, a pioneering surgeon who helped develop blood plasma and blood banks in the early years of World War II. City Council member Charlene Drew Jarvis (D-Ward 4), Drew's daughter, is a cousin.

Educated in the best of universities since before the turn of the century and trained to excel in their professions, the Drews and the Gregorys always had aimed high, but none had ever literally set their sights on the stars.

Gregory's mission is the second in which space scientists will conduct experiments from within Spacelab, a 23-foot-long laboratory that fits inside the shuttle's cargo bay. NASA officials said the flight will concentrate on processing materials in low gravity that could lead to breakthroughs in the production of special medicines and alloys.

NASA spokesman Leon Perry added, however, that Gregory's selection as shuttle pilot, which places him in line for command on his next flight, represents a breakthough of its own kind -- "another clear indication to the people of this country that black Americans can participate in all endeavors, fully, if allowed the opportunity."

"When you look at the shuttle program," Gregory said, "it looks essentially lily white. And it is, essentially because we have not been in the schools to study the proper kinds of courses and go to the military schools . . . and get in the pipeline." Gregory was selected in 1978 to be one of 35 new shuttle astronauts, including two other blacks and six women, from more than 8,000 applicants. The only black in the class of 1964 at the U.S. Air Force Academy, Gregory entered pilot training school after graduation and received his wings as a helicopter pilot. He served a stint in Vietnam in 1966 and 1967 flying rescue helicopters, and then was retrained as a jet fighter pilot.

A short time later he told his mother he wanted to be a test pilot.

"I was not surprised," said his mother, Nora Drew Gregory, a widow who still lives in the handsome, two-story brick house in the Fort Dupont area of Southeast Washington where her only son was raised. "When you have a child who grew up the way he grew up, you learn to grow up with him."

Gregory said he flew more than 40 different types of aircraft, from massive troop transports to one-man gliders, as a research-engineering test pilot, first for the Air Force and later for NASA.

"After doing that for a while, it was time to move on to something else," he said. "The next logical step was space."

Shortly after he decided to apply for the shuttle program, he received a phone call from a group called the Tuskegee Airmen, founded by a historic band of black aviators who were then urging young black fliers to help end the segregation of outer space.

Gregory said the group's name, at first unfamiliar, brought back boyhood memories of proud men who came to his home to reminisce with his father, Francis, who once taught at Alabama's Tuskegee Institute. They talked about the special magic of flying and their exploits high over Europe during World War II.

"Gen. Benjamin O. Davis and a lot of people talked about being in this flying unit and what they did in the Second World War," Gregory said. "I didn't realize that the services were segregated and that there was a unique black flying organization."

When Gregory was named an astronaut candidate in 1978, he joined the Tuskegee Airmen. And after his space flight, he said, he is looking forward to meeting with some of its members. "Maybe I'll have something to contribute," he said.

Arrington Dixon, former D.C. City Council chairman and a lifelong friend of Gregory's, said Gregory always had an understated air, all the way back their days as Boy Scouts.

"He was a serious kind of person even then," Dixon said. "He would put together model airplanes and had a dry wit I think he got from his father."

Some of his fellow cadets at the Air Force Academy said they never really noticed Gregory, even though he was one of a small number of blacks attending the school.

"I didn't know Fred personally while there," said Col. John Hoffman, director of tests at Andrews Air Force Base. "He was not one of those kind of guys that you would say, 'Gee, he's going to be a general or an astronaut someday.' "

But Frederick Douglass Maise, a retired Boy Scout official in the Washington area, said recently that he remembered Gregory as "the kind of person you would like to be or like your kid to be."

"His upbringing was top drawer," Maise reflected. "He came from well-educated people . . . . he grew up in a family in which he was the only child and he got all kinds of consideration."

An MIT-trained electrical engineer, Francis Gregory, who died in 1977, could not get work in his profession because of his race. So he turned to teaching, eventually becoming the assistant D.C. school superintendent for vocational education. Friends and relatives said he channeled much of his ambition into his son.

Fred Gregory's childhood environment was a protective one. "We lived in a kind of cocoon," said Gregory's wife Barbara. "We had everything white society had, but no one knew it but us."

"He didn't grow up with bitterness," Nora Gregory said of her son. "I'm sure [racial] things happened to him, but he rolled with the punches . . . . We told him to learn and prepare yourself. Read and be able to express your thoughts, and someday your day is coming." It was a creed of families like the Drews and the Gregorys: If not for you, then for the children.

Gregory said he worries that many black children grow up believing their horizons are limited. Until more blacks begin seeking careers in space travel, Gregory said, "I am feeling like a dinosaur up here. If blacks don't decide to come in this program, we are just going to be extinct." On a chilly February day, Fred Gregory left his astronaut chores in Houston and boarded a commerical jetliner for Washington. Soon after landing, he was President Reagan's guest at a White house luncheon honoring the founding of the Boy Scouts of America 75 years ago.

The White House was fine, but Gregory was happy just to relax in his childhood home, built by his parents when he was 6 months old. "Growing up here you were aware you could be an achiever if you wanted to," said Gregory. "I think it's whatever you want to make of it."

Fred Gregory was born Jan. 7, 1941, at the old Freedmen's Hospital. "He was a most welcomed baby," Nora Gregory said of her son. "We wanted a big family, but we got all the best things in one little boy."

The Drews and the Gregorys belonged to a stable, well-educated black middle-class, a group that bought homes and sent its children to college, even if that meant someone had to take multiple jobs to make ends meet.

"We were just gentle people growing up in Washington," recalled Nora Gregory, "trying to make sure our children had as many advantages . . . so they could be happy, move up and bring their family up with them."

If the schools were to be segregated, the black schools would be among the best. If black Boy Scouts, segregated in the early 1950s, didn't have a campground, their parents would carve one out of the woods. And if Fred Gregory wanted to be a pilot and needed to go to the Air Force Academy to accomplish it, his father Francis would walk the halls of Congress until he found a legislator willing to sponsor his son.

Parents had to become masters of compensation, they said. For example, Francis Gregory became concerned that his son's college preparatory curriculum did not include shop classes. A firm believer that every man should know how to use his hands, he took to the back yard with his son after school, building a garage that still stands.

City Council member Jarvis said Gregory was fortunate to have his father's full attention when he was growing up.

In almost anything he wanted to do with his life, Gregory said, "my parents said, 'Go for it, and we'll be right there to help you out.' "

That attention included a succession of collies named Ricky. It also included a speedboat that the Gregorys kept in the garage.

"I wanted to race boats," Gregory said. "We got probably the cheapest boat that was possible to be bought." He said he and his father "got this boat fast enough to compete in any race I wanted to.

Gregory added, "My father allowed me to go on Boy Scout trips to California and New Mexico when we really couldn't afford to do it. It was just the kind of support he gave me."

While it lent to the development of leaders and achievers, that kind of support also put the family in what was deemed a privileged class, set apart from many black Americans who had fewer opportunities.

Fred Gregory recalls that the family often went to Highland Beach, a Chesapeake Bay resort established by a son of abolitionist Frederick Douglass and frequented by educated, upwardly mobile families like the Drews and the Gregorys.

But Nora Gregory said, "I don't like this thing about a black elite. There was no elite." Friends of the family remember the Gregorys' home being open to all kinds of people.

"Freddie and his family transcended that in a very sensitive way," said former City Council chairman Dixon. "His mother and dad and Freddie, too, were part of all communities -- black and white and incomes all across the board."

In 1872, Gregory's great-grandfather, James Monroe Gregory, was a member of Howard University's first graduating class, which consisted of himself and two women. He became a professor of Latin and mathematics at Howard and pushed for greater civil rights for blacks, according to university records.

The Gregory family became middle-class, but not wealthy. "My father's father was . . . . a very successful carpet layer and became active in the union," Fred Gregory said. "My mother's father was a Peoples Congregational minister. He went to Amherst and Yale divinity. But again [it was done with] essentially no money, borrowing money, working very hard to go through school."

Gregory said he felt "pressured" to attend a prestigious New England college because many of his relatives had, and so he enrolled first at Amherst. But he dropped out after a year because he "never really fit," came home, and became interested in flying and the Air Force Academy.

Getting into the academy required a letter of recommendation from a congressman, and the District of Columbia had none. "There were six to eight black congressmen, and we went to each one of them," Gregory said of his and his father's efforts.

Finally, New York Rep. Adam Clayton Powell recommended Gregory for an alternate slot, giving his principal support to a New York youngster. But it was enough to get Gregory in the 1960 freshman class at the academy. Upon graduation he took additional training, earning his wings and decorations for his flying in Vietnam.

Shortly before he became an astronaut, Gregory received a master's degree in information systems from George Washington University.

His wife, Barbara, has recently completed her master's degree in psychology. With both their children in college, the two said they lead a quiet life.

And yet, Gregory's mother, like most mothers, said she still worries about her son.

"When I actually look at the shuttle and watch all the fire when it goes up in the sky, I say 'God take care of him,' " Nora Gregory said. "That's what I've been saying since the day he was born."