Forestalled by gloomy weather at the Kennedy Space Center, flight officials waved off the space shuttle Discovery's landing Monday, deciding to wait 24 hours and try again.

Discovery had already canceled a landing attempt on its first reentry orbit and was getting ready for a second pass at 5:05 a.m. Eastern time when NASA shuttle communicator Ken Ham called mission commander Eileen Collins.

Weather over the 15,000-foot runway at the center's Shuttle Landing Facility was still "unstable" with "potential for low clouds" and low ceilings, Ham said. A landing Monday, he said, was a "no go."

The shuttle will continue in orbit Monday and attempt a landing at the space center on either of two successive orbits Tuesday, at 5:07 a.m. or 6:43 a.m. If the weather continues to frustrate a return to the space center, Mission Control will default to Edwards Air Force Base in California.

Thunderstorms and occasional torrential rains drenched the space center Sunday for much of the afternoon and evening, which is not unusual for central Florida, but skies had begun to clear markedly by early Monday.

Up in Discovery, orbiting 220 miles above Earth, Collins and the rest of the seven-member crew went through their de-orbit checklists without incident and closed the shuttle's payload bay doors at 2:26 a.m.

The critical reentry sequence begins with a "de-orbit burn" a little over an hour before landing. The shuttle, pointed in the direction of travel and flying upside down, uses the burn to adjust its trajectory and right itself until the nose is pointed forward and upward at an angle of about 40 degrees.

As burn time approached for the first landing attempt at 4:47 a.m. Monday, astronaut Kent V. Rominger took off from the space center in a shuttle training aircraft to look at nearby cloud banks, adding a first-person assessment to local weather forecasts being evaluated by Mission Control in Houston.

There, after polling his team about 20 minutes before the scheduled burn, NASA flight director Leroy Cain ordered a "wave-off" because of low broken clouds and a potential for rain showers.

At the landing facility, scattered puffs of cloud scudded over the tarmac, with a more formidable cloudbank hovering over the nearby Atlantic Ocean. In the interval between the first pass and the second, at 6:22 a.m., the weather appeared to clear.

But not enough. Cain polled his team again, and with only 10 minutes left before the scheduled burn, waved off Discovery until Tuesday, with Edwards Air Force Base, in the high desert east of Los Angeles, as the backup landing site. NASA also will open a third alternative at the White Sands Missile Range in New Mexico.

"The second opportunity was clearer than the first," Cain said of Monday's attempts, in a NASA TV interview at Mission Control. "But I couldn't get comfortable with the overall condition."

The postponed landing was the latest in a series of unplanned events that have interfered with the smooth execution of Discovery's mission.

Discovery is undamaged and functioning almost perfectly, but during launch its external fuel tank shed large pieces of foam insulation similar to those that doomed the shuttle Columbia 21/2 years ago. NASA officials have grounded the shuttle fleet until the cause of the foam loss is found and fixed.

Discovery also needed an unplanned spacewalk to remove two pieces of heat shielding protruding from its underbelly, and planners decided to bring the orbiter home despite a fraying thermal blanket on its fuselage.

Spokesman George Diller, standing next to a monitor showing cloud cover over much of Florida, explains NASA's decision to delay the landing.