As the space shuttle Columbia touched down on a California runway yesterday morning, the men who run things at Mission Control in Houston took off their headphones and applauded the successful conclusion of one more voyage into space But, for at least one of these men, the cheering signaled far more than just relief. With the end of the Columbia's fifth space flight, astronaut Jeffrey A Hoffman moved one step closer to his long-awaited first day in space.

The 38-year-old Hoffman, who received a Ph.D. in Astrophysics from Harvard in 1971, is believed to be the only one of the 79 U.S. astronauts with a Harvard background. Selected in 1978 as a mission specialist for the shuttle program. Hoffman belongs to a new breed of space scientist--a generation of astronauts quite distinct from the toughened test pilots who grabbed the world's attention during the pioneering Mercury. Gemini and Apollo programs

Hoffman and the other 19 mission specialists selected with him in 1978 are scientists and engineers--not pilots--by training As such, they have been trained to take care of everything except actually flying the ship, which is left to shuttle pilots. And for Hoffman and his colleagues, the shuttle flight which touched down yesterday morning marked a special hurdle Astronauts Joseph Allen and William Lenoir--who launched the shuttle's cargo of two commercial satellites were the first two mission specialists ever to fly in space

Hoffman and his colleagues differ from their predecessors in another, perhaps even more important, way When the National Aeronautics and Space Administration (NASA) in 1978 announced the selection of the astronaut group that included Hoffman, a reporter asked the director of the Manned Space Flight Center in Houston to comment on his new charges Christopher C. Kraft Jr. said the new astronauts--the first picked by NASA in more than eight years--were "extremely highly qualified and motivated, because, unlike previous applicants, many have wanted to become as turnouts since they were 10 or 12 years old."

In Hoffman's case, Kraft was a few years off

"I was basically interested in space since I was six," Hoffman says. "Rockets were the neatest things around." He recalls having a avid interest in science fiction, and being fascinated by the stars when he visited the planetarium or peered through his father's telescope.

But because the early astronauts were of the test-pilot school and a little closer to American hero status then he ever dreamed of being, the Brooklyn-born Hoffman says he "didn't relate to the space program personally." The astronaut recalls that he never talked about his ambition, keeping it secret even from his parents "because it seemed sort of frivolous." Nevertheless, he adds, "I was dead serious about it."

In 1962, just as the space program was beginning to mature--and the same year that John H. Glenn Jr. became the first American to orbit the earth--Hoffman graduated from Scars dale High School. At Amherst College, Hoffman followed his scientific bent, majoring in Astronomy, and graduating first in his class,summa cum laude. Then, without skipping a beat, Hoffman arrived at Harvard to embark on three years of gamma ray research. This work took him as far away as Argentina, where he experimented with a balloon-borne gamma-ray observatory that he designed and built.

Giovanni G. Fazio, a lecturer on Astronomy who worked with Hoffman at Harvard, says that Hoffman was "very energetic" in his desire to find sources of certain cosmic rays The balloon experiments, he adds, were designed to lift instruments above those levels of the atmosphere that could interfere with the "search for radiation from celestial objects."

Following his Ph.D. Hoffman received a string of fellowships that began with more gamma ray research at the Harvard-Smithsonian Astrophysical Observatory, and eventually led to a three-year stint with a prestigious astronomical organization in England, where he met his wife, Barbara.

From his post in England, where he participated in a satellite project. Hoffman was invited in 1975 to work in MIT's Center for Space Research. As MIT scientist Walter Lewin recalls. Hoffman's work there with two astronomical satellites helped lay the groundwork for an important new theory on the source of X- rays in space

"Those were incredibly exciting years." Hoffman says of his time at MIT, where he actually helped control and monitor one of the satellites be worked on.

"Jeffrey is one of the most conscientious people," Lewin says of his former colleague adding that he is "happy, as a taxpayer, to know that people like him are working in the government."

For a while however. Hoffman never thought be would have a chance to work for the government --or at least for NASA. But in 1977, Hoffman saw a poster in an MIT lab announcing NASA's recruiting drive.

"Given an opportunity to apply there was no way i could say no, Hoffman says. But the odds were not encouraging: out of 8079 applicants for pilot and mission specialist openings, NASA selected 20 mission specialists and 15 pilots. After first making the finalists group of 208, Hoffman was flown to Houston for a week of interviews and medical exams. Shortly thereafter, many of Hoffman's relatives, friends and colleagues started getting calls from the FBI, inquiring about all the personal details that NASA needed to know before putting someone in the back seat of their billion-dollar space plane.