Inspectors found a 5-inch-long crack in the foam insulation covering the shuttle Discovery's external fuel tank, and NASA managers were deciding Monday whether to call off the scheduled Fourth of July launch.

The Space Shuttle Discovery is pictured on Pad 39B at the Kennedy Space Center in Cape Canaveral, Fla., on Sunday, July 2, 2006. NASA officials scrubbed the planned launch of mission STS-121 Sunday because of weather. The mission, which was also scrubbed on Saturday, is now scheduled for Tuesday, July 4, 2006.¡¡[AP]

The crack was spotted during an overnight inspection. NASA had scrubbed launch plans Saturday and Sunday because of poor weather and had removed fuel from the tank.

The inspectors found the crack, which was an eighth of an inch deep, in the foam on a bracket near the top of the external fuel tank.

"We don't know if it's a problem or not," NASA spokesman George Diller said Monday.

Officials were meeting to determine whether it could be fixed for a Tuesday liftoff.

If NASA decides to go ahead with the launch Tuesday, it would be the first manned launch by the United States on the nation's birthday, and only the second liftoff of a space shuttle since the 2003 Columbia disaster.

Concerns about cracks in the fuel tank's foam insulation have dogged the program since Columbia exploded over Texas on Feb. 1, 2003. A chunk of flyaway foam had damaged Columbia's wing during liftoff, allowing superheated gas to penetrate the shuttle when it re-entered the atmosphere.

NASA tried to fix the problem before trying another launch, but more foam broke off Discovery's redesigned tank last July, barely missing the shuttle.

NASA Administrator Michael Griffin decided the shuttle should go into orbit despite the concerns of two top agency managers who wanted additional repairs to the foam insulation.

The mission for Discovery's crew this time is to test shuttle-inspection techniques, deliver supplies to the international space station and drop off German astronaut Thomas Reiter for a six-month stay.

The weather forecast for a Tuesday liftoff was better than it was on Sunday or Monday, with a 40 percent chance that storms at launch time would prevent liftoff, said U.S. Air Force 1st Lt. Kaleb Nordgren, a shuttle weather forecaster. NASA planned to make launch attempts on Tuesday and on Wednesday if necessary.