Atlantis may be ready for launch on a secret military mission as early as Nov. 15, no more than six days behind schedule, if work to fix problems with the ship's spy satellite payload goes well, sources say.

In addition, NASA managers are leaning toward waiving an internal agency rule requiring three weeks between shuttle flights, a move that would allow the recently repaired shuttle Columbia to take off on schedule around Nov. 30.One usually reliable source said agency officials decided Thursday to waive the rule, but that could not be immediately confirmed.

Atlantis and its five-man all-military crew were cleared Tuesday for blastoff on the 37th shuttle mission the night of Nov. 9 to carry a Pentagon spy satellite into orbit. But the Air Force announced an indefinite delay Wednesday, citing problems with the classified payload.

Sources initially said the flight faced a delay of at least a week to 10 days and possibly more than two weeks. Officials who asked not to be named said Thursday, however, that the problem did not appear to be as serious as they first believed and that Atlantis might be ready for flight as early as Nov. 15.

But under a Pentagon-imposed security blanket, NASA officials refused to discuss possible launch dates Thursday, saying when Atlantis takes off is up to the Air Force.

Engineers at nearby launch pad 39B, meanwhile, are readying the shuttle Columbia for blastoff on a 10-day astronomy mission that has been delayed since May by a series of hyrogen fuel leaks.

Before Atlantis was grounded, NASA managers hoped to launch Columbia around Nov. 30 in line with an internal space agency rule requiring three weeks between shuttle missions so data from one flight can be analyzed before launching the next.

But if NASA officials waive the three-week rule - and Atlantis takes off Nov. 15 - engineers at the Kennedy Space Center would be faced with launching two space shuttles within 15 days. But because Atlantis's mission is a classified Department of Defense flight, details about scheduling are difficult to confirm.

Even so, shuttle program director Robert Crippen said in a statement Thursday that Atlantis - mission STS-38 - still has priority over Columbia.

"At this time, we are continuing to proceed with the schedule to fly STS-38 before (Columbia)," he said. "I am optimistic about flying (Columbia) sometime in December."

Crippen did not address the three-week rule, saying only that Columbia would not be launched on mission STS-35 until data from Atlantis's flight can be studied.