Discovery at launch pad 39B following its rollout last month. Photo: NASA/KSC

Less than a day after NASA finally set a date for launch of its first shuttle mission since July, a new problem has cropped up that could force another delay.

Managers have ordered a re-inspection of a crucial area between the orbiter and its external fuel tank. The work, which can be done at the launch pad, will require technicians to disconnect ordnance devices and re-open an area already closed out for flight.

The reason for the re-inspection is a paperwork snafu. NASA officials, reviewing paperwork documenting the wiring inspections and repairs that have been under way for months, could not find evidence that one wire in particular which had been flagged for inspection, had been worked on, said NASA spokesman Bruce Buckingham.

"There's no paperwork to show that it had been inspected," said Buckingham.

Re-opening the compartment to check the wire will eat up all the extra time NASA had built into the schedule which culminated with the shuttle's launching at 12:13 a.m. ET on Dec. 11.

The flight, which is crucial to revive the dormant Hubble Space Telescope, could face additional delays. NASA has said it will not launch the mission after Dec. 14 to avoid flying over the Christmas holiday. In addition, officials do not want to have the shuttle in orbit during the transition to the year 2000 to avoid any potential problems with computer software.

Buckingham said workers will begin the re-inspection over the weekend and managers should be able to determine early next week if Discovery will be ready for flight on the 11th.

Meanwhile, shuttle managers decided Friday to replace one of Endeavour's three main engines because of concerns the powerplant was damaged during routine testing.

Space Shuttle Endeavour was moved to the Kennedy Space Center's Vehicle Assembly Building this week. Photo: NASA/KSC

A similar engine was found to have delamination on the wall of its main combustion chamber after undergoing the same testing procedures.

So as a precaution, the suspect engine will be removed from Endeavour and replaced with a spare. Endeavour's other two engines were not cited for concern.

The engine swap will occur inside the Vehicle Assembly Building. Endeavour was moved from its hangar to the 52-story building on Thursday to be attached to an external fuel tank and twin solid rocket boosters.

The extra work will delay Endeavour's rollout to launch pad 39A from December 7 to December 13.

The shuttle is slated to launch in mid-January on an 11-day mission to map the Earth's surface with radar.