CAPE CANAVERAL, Fla. (AP) _ NASA forged ahead today toward its second launch attempt for space shuttle Discovery and its double-satellite cargo.

Discovery is scheduled to blast off at 9:27 a.m. EDT Saturday, one week later than planned. Forecasters called for a 90 percent chance of good weather.

''We're sitting in good shape,'' shuttle test director Mike Leinbach said this morning. ''We're not working any problems.''

An abbreviated countdown was to start this evening at the 11-hour mark.

The first launch attempt was thwarted in the final two hours of the countdown last Saturday by a failed electronics switch that is supposed to activate the booster release system just before liftoff. The system turned on far too early.

Technicians replaced the 10- to 12-year-old switch earlier this week.

''It's just one of those things. Sometimes the hardware's good, sometimes it's not,'' Leinbach said.

''I suspect if you take all the launch attempts over the last three or four years, it probably averages out to launching on the first attempt about half the time,'' he said.

Discovery's nine-day flight features two satellite releases, the retrieval of one of those satellites, and a spacewalk by two of the five crewmen to test tools needed for the Hubble Space Telescope repair mission this winter.