NASA has decided to remove and inspect engine pumps aboard the shuttle Discovery, revising the launch processing schedule and making it virtually impossible to meet an Aug. 4 target date for the first post-Challenger launch, sources say.

While Aug. 4 remains the official target, the launch schedule has been so severely compressed there are no "contingency" days left in the processing flow to handle unexpected problems, including weekends.A NASA management council meeting April 14 at the Johnson Space Center in Houston is expected to result in a new internal launch target date and sources said Friday that Aug. 11 was one possibility.

But they said launch would not be rescheduled for the week of Aug. 15 to avoid a conflict with the Republican national convention, despite NASA Administrator James Fletcher's previous claims that election-year politics would not play a role in any launch decision.

Under the new launch processing schedule at the Kennedy Space Center, Discovery will be attached to its external fuel tank and redesigned solid-fuel boosters May 22, a week behind schedule. The shuttle, mounted atop a squat mobile launch platform, then will be rolled to launch pad 39B around June 1.

Once at the pad, engineers will prepare the spaceship for a crucial flight readiness firing, or FRF, on June 22 in which all three of the orbiter's liquid-fueled main engines will be fired for about 20 seconds in an overall test of the shuttle system.