Fuel Leak Prompts NASA to Scrub Launch of Shuttle : Space: Engineers notice the problem when they begin pumping liquid hydrogen into Columbia. A new liftoff time could be announced today.

The launch of the space shuttle Columbia was scrubbed Tuesday when liquid hydrogen began leaking into the craft’s engine compartment shortly after engineers started pumping the highly explosive fuel into the shuttle’s main tank in preparation for a night launch.

The launch, already two weeks behind schedule, was postponed for at least 24 hours, but it probably will be delayed longer than that because it could take some time for engineers to determine the cause of the leakage, officials said.

Although liquid hydrogen is explosive when it comes into contact with liquid oxygen--the other component in the shuttle’s main fuel system--engineers insisted Tuesday that the vehicle was not in danger of exploding because the problem was detected when only a trace amount of vapor was found in the engine compartment.

“They shut it down to be safe,” said Patricia Phillips, a spokeswoman for the National Aeronautics and Space Administration. “You simply cannot have excess hydrogen in what amounts to a controlled explosion at liftoff.”

Engineers were to work through the night to try to determine the nature of the problem, and a new launch date was expected to be announced sometime today.

The launch had been set for 9:38 p.m. PDT. The 10-day mission is the first to be devoted to a single scientific discipline. The crew had not boarded Columbia when the launch was scrubbed at 3:25 p.m.

Manned by seven astronauts, the largest crew since the January, 1986, Challenger explosion, Columbia will be carrying the Astro observatory: three ultraviolet telescopes and one X-ray telescope that will photograph the universe at wavelengths normally obscured by the Earth’s atmosphere.

The astronauts will operate the four telescopes around the clock for nine days, and perhaps 10 if their maneuvering fuel holds out, before packing them up and bringing them home for reuse on a later shuttle mission.

Over the course of their mission, the astronauts are scheduled to make as many as 300 separate observations of objects ranging from Comet Austin, which last week made its closest approach to Earth, to quasars at the edge of the universe--and all at wavelengths that, because they are absorbed by the atmosphere, have rarely been studied by astronomers in the past.

On this fourth shuttle mission of 1990 and the 36th overall, the astronauts also will conduct an astronomy lesson from space for high school students, and payload specialist Ronald A. Parise will use a ham radio to attempt to make contact with cosmonauts aboard the Soviet space station Mir.

The two spacecraft will have to be within 2,400 miles of each other for Parise to make contact. If the attempt is successful, it will mark the first time that astronauts and cosmonauts have had a direct radio link. In the historic 1975 Apollo-Soyuz linkup, all communications between the two craft were handled through ground communications centers.

Columbia commander Vance D. Brand, who was a crew member on that linkup, has been brushing up on his Russian for the occasion.

Brand, 58, a former aviator in the Marine Corps, will be making his fourth space flight. In addition to the Apollo-Soyuz mission, he was commander of the fifth shuttle mission in 1982, which was the first to launch a commercial satellite, and commander of a 1984 mission.

Pilot Guy S. Gardner, 42, is an Air Force officer who flew 177 combat missions in Southeast Asia in 1972 before becoming a test pilot instructor. This will be his second shuttle flight; he was pilot of a Defense Department mission in December, 1988.

Mission specialist John M. (Mike) Lounge, 43, is chief of the Space Station Support Office, which is designing the Freedom space station. He will be making his third shuttle flight. He was a mission specialist on an August, 1985, flight in which an Australian communications satellite was launched and an American satellite repaired.

The remaining four crew members all have doctorates in astronomy or astrophysics.

Mission specialist Jeffrey Hoffman, 45, will be making his second flight. In April, 1985, he made the first unscheduled spacewalk in an unsuccessful attempt to rescue the malfunctioning Syncom IV-3 communications satellite.

Parker, 53, also will be making his second flight. A Caltech graduate, he worked on the first Spacelab mission in November, 1983.

Parise, 38, and Samuel T. Durrance, 46, will be the first non-astronauts to fly on the shuttle since the Challenger accident. Parise is an employee of Computer Sciences Corp. of Silver Spring, Md. Durrance is a faculty member at Johns Hopkins University in Baltimore.

Maugh reported from Kennedy Space Center and Dye from Los Angeles.