NASA managers Friday debated launch dates for the shuttle Discovery's blastoff later this month on the first post-Challenger mission amid work to prove a small hydrogen leak will not occur during flight.

The Johnson Space Center near Houston remained closed Friday because of the threat of Hurricane Gilbert, but the giant storm appeared to be heading for landfall well away from the shuttle mission control center.NASA hopes to launch Discovery the week of Sept. 26, but managers decided Wednesday to put off announcing an official launch date until after the hydrogen leak was resolved and after the impact of Gilbert was known.

It was possible a launch date announcement could be made by late Friday, but a key test to isolate the leak was not scheduled to be completed until Saturday and the announcement likely would be delayed to next week.

In the meantime, sources said Discovery could not be ready for blastoff before Sept. 27.

The hydrogen leak was discovered during a recent test in which the fuel line system in Discovery's engine compartment was pressurized with an inert gas. By monitoring how fast the pressure dropped off, or decayed, engineers could determine if any leaks were present.

During two test runs, pressure dropped off faster than allowed, and engineers worked through the week to pin down the source of the presumed leak.

A NASA spokeswoman said it was believed the pressure drop was caused by a hydrogen "fill and drain" valve that did not close tightly in the absence of hydraulic pressure.