NASA hopes to hold the latest space shuttle Discovery launch delay to no more than two days, but won't set a new date until Wednesday, after a new electronic part has been checked.

The liftoff, which had been set for Saturday after three earlier postponements, now will occur no earlier than 8:08 a.m. EST March 13.The latest setback occurred Monday when a prelaunch test disclosed the failure of a "Master Events Controller," a vital system that commands separation of the booster rockets and the external fuel tank from the shuttle in flight.

Engineers replaced the failed unit with one borrowed from sister ship Columbia and were to test it on the launch pad Tuesday afternoon. The testing was delayed so that explosive devices throughout the spaceship could be disarmed to avoid an accidental firing.

The explosives are fired in flight to separate such things as the spacecraft from the launch pad and the booster rockets and external fuel tank from the spaceship.

Officials were worried that any extended delay could affect the launch period for the high-priority Atlantis mission that is to propel the Magellan probe out of Earth orbit toward Venus.

NASA has said if Discovery, which is to carry five astronauts, could not be launched by March 18, it might have to yield the pad to Atlantis, set for liftoff April 28. If Magellan can't be launched between that date and May 23, the planet will not be in proper position again until 1991.

Discovery is to make the third shuttle flight since the Challenger explosion killed seven astronauts more than three years ago.