With just one day left before launch, NASA scrambled Wednesday to investigate a potential problem with the landing gear on space shuttle Columbia, poised to take off for a service call to the Hubble Space Telescope.

The space agency also braced for unusually cold weather that could force a flight delay. Temperatures were expected to drop to 38 degrees at the time of Columbia's planned 6:48 a.m. launch on Thursday.

The landing gear issue arose during a high-level meeting of mission managers on Tuesday afternoon. By Wednesday morning, three engineering teams were working on the problem in hopes of getting "comfortable" with it in time for Thursday's launch, said NASA spokesman George Diller.

Eight wheel bearings in Columbia's main landing gear evidently were treated with 300-degree heat before installation, rather than the 500 degrees intended to keep them from breaking during touchdown, Diller said. Engineers were trying to determine if the temperature difference may have weakened the bearings.

"They're starting to get comfortable with it, but there's still a lot more data analysis to do," Diller said.

Shuttle program manager Ron Dittemore said a wheel bearing failure during landing could be disastrous.

"If you lose the bearing, its ability to take the load in the bearing, then your wheel isn't going to turn very well and it could lock up under heat or friction and then you've got a real problem going down the runway at landing at 200 mph," Dittemore said. "The wheel doesn't roll, it starts to skid. That would be a real bad day."

Replacing the bearings, if necessary, would require weeks of work back in the shuttle hangar.

Meanwhile, forecasters said there was a 40 percent chance that Thursday's cold could delay the launch. Warmer weather is expected Friday.

Extreme cold could damage some shuttle systems, including the extensive fuel plumbing, and could increase the buildup of ice on the external fuel tank. The concern is that chunks of ice could fall off during liftoff and strike Columbia.

NASA has been wary of cold weather ever since the 1986 Challenger disaster. The temperature was 36 degrees on the January morning when Challenger lifted off, and had been well below freezing during the night. The cold caused O-ring seals to fail in the right solid-fuel booster rocket and allowed blazing hot gas to leak.

However, redesigned booster rockets now have heaters to prevent the rubbery O-rings from deteriorating in cold weather.

Once they arrive at Hubble, Columbia's astronauts will install an advanced camera, a refrigerator system to resuscitate a disabled infrared camera, new steering mechanism and power-control unit, and stronger solar wings for generating even more electricity. The flight will last 11 days.