Florida ? NASA is repairing a leaky hydrogen gas line on Endeavour’s fuel tank in hopes of launching the shuttle on its space station construction mission Wednesday, four days after the first try was called off.

But another NASA mission, involving a pair of science spacecraft bound for the moon, is scheduled to blast off Wednesday. Top space agency officials will decide today whether to bump the moon mission to make way for Endeavour.

The same kind of leak postponed a shuttle launch in March. Technicians replaced the vent line hookup and a pair of Teflon seals back then, and the leak did not recur. NASA is hoping for similar results this time. The hookup and seal replacements on Endeavour’s tank were expected to be completed this morning.