Euphoric NASA engineers, hailing the "rebirth" of America's space program, stood by Wednesday to begin attaching the shuttle Discovery to its external tank and boosters for the first post-Challenger flight.

Discovery, cheered on by hundreds of proud NASA workers, was towed Tuesday to the Vehicle Assembly Building, the first movement for the orbiter since it was put in its hangar Oct. 30, 1986 - exactly 600 days ago. Its next stop: launch pad 39B for blastoff on the 26th shuttle mission late this summer."This was like a rebirth," said John "Tip" Talone, the NASA engineer in charge of Discovery's ground processing. "This was like saying we're back in business again and we mean to stay in business."

Discovery's crawl from its hangar to the assembly building was a clear sign of the growing pace of launch processing and NASA's determination to resume American manned space flights late this summer, after a 21/2-year hiatus caused by the January 1986 Challenger disaster.

"That's the cleanest orbiter we've ever moved, and it's just in great shape," said Forrest McCartney, director of the Kennedy Space Center. "I don't know of any single thing about that orbiter that we're concerned about."

Engineers planned to pick up the orbiter Wednesday with a pair of overhead cranes to begin the process of bolting Discovery to its external tank and Morton Thiokol-made boosters. The roll out to the launch pad is expected around the end of the month.

Under that schedule, Discovery would blast off around Sept. 3, but NASA hopes to make up time later in the processing "flow," and the launch could slip back into August.