The leak-plagued shuttle Columbia will be grounded until at least late November, after the Oct. 5 launch of the shuttle Discovery and after a flight by Atlantis around Nov. 7, NASA officials say.

"Both Discovery and Atlantis are operational orbiters with no known or suspected defects," said William Lenoir, NASA's associate administrator for space flight. "Our highest priority is going to be to resume flights with Discovery and Atlantis as scheduled."In the meantime, "Columbia is grounded," Lenoir said. "The highest priority in working on Columbia is to find the leak, fix same and verify that they're fixed. Then and only then will we look at returning to flight."

Originally scheduled for launch May 30, Columbia was grounded Monday, the night before its fourth takeoff try, when explosive hydrogen began building up in the shuttle's engine compartment.

Later, during a series of tests, a fuel line valve leading to main engine No. 2 refused to close properly on command, a failure that likely would have delayed launch regardless of any leakage.

A replacement valve from the shuttle Endeavour cannot be delivered to the Kennedy Space Center until Sept. 28. Given Discovery's planned Oct. 5 launch target, it is unlikely another fueling test to pinpoint the leak can be conducted with Columbia until after its sistership is off pad 39B.