Flooded runways at California's Edwards Air Force Base may force the space shuttle Columbia to land instead at the White Sands Missile Range in southern New Mexico at the end of the shuttle's maiden flight next month.

"We'll just hope that the lake bed at Edwards dries out, and if it doesn't we'll have to go to White Sands," Space Shuttle Commander John W. Young said yesterday at a news conference at the Johnson Space Center in Houston. "It's something that has to be watched in a real time."

A spokesman for the National Aeronautics and Space Administration at Edwards said that an inspection of the runways last Friday suggested it might take at least four weeks for the shuttle runway to dry out after a torrential rain flooded it last week. The spokesman said there is at least an inch of water still covering most of the runway, which could force the Columbia to skid and crash when it lands at 200 miles an hour next month.

Young and co-pilot Robert Crippen are to take Columbia into orbit for the first time April 7, launching from Cape Canaveral, Fla., then returning to Earth and landing the space shuttle like an airplane April 10. The runway at Edwards designated for the landing is a normally dry lake bed 300 feet wide and 5.2 miles long located at the northern end of an Air Force reservation used for years to land rocket-powdered test aircraft.

The astronauts have practiced landing countless times in jet aircraft at both Edwards and White Sands, where there is at least one dry lake bed as wide and almost as long as the runway at Edwards. The runway at White Sands is located in a huge valley between two mountains and is not as hard as the one at Edwards.

The astronauts also have practiced landing at a three-mile-long concrete runway at the Kennedy Space Center, a runway they will use only if they lose an engine during their first four minutes of flight from Cape Canaveral. They can also make emergency landings at Rota Naval Base in Spain, at Hickam Field in Honolulu and at Kadena Air Force Base on Okinawa should they fail to reach orbit or should they have to return to Earth in a hurry.

"If we lose an engine and have to land in Spain, that will be the fastest transatlantic crossing you've ever seen," Young said jokingly. "Once in orbit scarely an orbit will go by when we don't have a chance to come down at one of these contingency sites."

NASA said that it hopes to know 10 days before Columbia takes off if the landing will have to be rerouted to White Sands so support equipment can be moved there from Edwards, but a spokesman said a decision could be made as late as 36 hours before the landing.

Even then, Young said, he could retarget Columbia's landing site 30 minutes before starting its descent to Earth. Said Young: "We plan to have good weather for this flight but if there were a thick overcast layer at one of the lake beds, we'd just take it in to the other lake bed."