Frustrated NASA engineers are leaning toward replacing a sluggish 1-inch fuel valve that derailed the shuttle Discovery's main engine test firing, a move that would delay the crucial test about a week, officials said Friday.

But officials emphasized that no final decisions had been made and that the issue was on the agenda for a meeting of NASA's management council, made up of top agency officials, including shuttle chief Richard Truly and Frederick Hauck, commander of the first post-Challenger mission.The council began meeting at 9:30 a.m. and a decision on the engine valve issue was expected late Friday. In the meantime, engineers proceeded with readying Discovery for an engine firing attempt Sunday should managers elect to proceed without replacing the suspect valve.

The first attempt to fire Discovery's three hydrogen-fueled engines was aborted Thursday at 7:30 a.m. an instant before flight computers were to issue ignition commands at the T-minus 6.6-second mark in an otherwise smooth-running countdown.

The culprit was a small hydrogen "bleed valve" in main engine No. 2 that did not close before the engine start command as fast as the engine's control computer was programmed to expect.

Engineers ran tests overnight to find out if the valve's performance could have been affected by exposure to liquid hydrogen fuel at 423 degrees below zero. If so, computer programs could be changed that would permit the engine to operate, despite a slow-moving valve.

Under that scenario, Discovery could be ready for a second engine firing attempt Sunday at 7:30 a.m. - a full week behind schedule.

While the software option had its supporters, engineers early today were leaning toward replacing the valve with a unit already on hand.

Boyce Mix, a top NASA engine expert, said replacement would take about five days: one day to get into Discovery's engine compartment, three days to replace and test the valve and another day to close the engine room. The countdown then could resume for an engine firing late next week.