NASA officials, acknowledging they made mistakes because of schedule pressures, yesterday discussed their new plan to get the space shuttles flying again, beginning in early October, after five months of launchless torment while engineers played hide and seek with a series of hydrogen leaks.

The shuttle Columbia, which since May has sprung leaks apparently in three locations, will be grounded indefinitely while a special team of experts, detailed to the Kennedy Space Center for the duration, has found and fixed all the holes.

"We've bought them all one-way tickets to the Cape," said William B. Lenoir, who heads NASA's office of space flight. "They don't get to come home until they've found the leak."

Shuttle chief Robert L. Crippen appointed veteran propulsion expert Robert Schwinghamer, a top engineering official at Marshall Space Flight Center in Huntsville, Ala., to head the nine-man team. Previously, officials at Johnson Space Center in Houston had directed the investigation. Most of the members of the new team were already involved with the search for the leaks but now they have been freed of all other duties and their work is to go on around the clock.

Meanwhile, Lenoir said, since there is no evidence that the shuttle Discovery has any leaks, it will be prepared for a launch as early as possible -- probably around Oct. 8 -- on a mission to deploy the Ulysses probe that will study the sun. And the shuttle Atlantis, which also sprang a leak this summer, has been repaired and will be readied to fly a secret military mission in early November.

Ulysses, a high-priority joint mission with the European Space Agency, must be launched between Oct. 5 and Oct. 23 to reach its required position, or wait another 13 months.

It was this narrow "window of opportunity" for launching Ulysses that had driven many of the shuttle managers' decisions in dealing with the hydrogen leaks, Lenoir said.

Now that there is no pressure to launch Columbia ahead of Ulysses, the investigators can do a more thorough investigation, he said. "Ulysses was the thing driving us all along."

Because of that pressure, "We more or less defaulted" into pursuing a single line of inquiry, instead of a more exhaustive investigation of all possible sources of leaks, he said. "We got rushed . . . and decided to take our best shot."

Engineers repaired what they thought was the problem but found they were dealing with several elusive leaks which showed up only when supercold liquid hydrogen was being loaded into the shuttle and not in pre-launch tests, which use different conditions. Engineers believe the leaks had at least two unrelated causes -- microscopic glass beads that may have gotten into the pipe fittings at one site, and hardware improperly assembled at another.

But Lenoir added that, given the information available at the time, he probably would make the same decisions again.

While their gamble made them prey to public embarrassment, NASA officials have emphasized that it did not jeopardize the safety of the shuttle or crew because -- as events seemed to prove -- sensors in the shuttle and other safeguards will prevent a launch if dangerous concentrations of hydrogen are present.

But the long flightless summer has embarrassed the agency and raised questions about its quality control and management at a time when the administration has called for funding increases for a much more ambitious space exploration program. The problems have also intensified doubts about the wisdom of proceeding with an already-controversial, $37 billion space station -- which relies on the shuttle for its construction and maintenance.

Officials also said they are reviewing their system of testing for leaks, which failed to catch any of those encountered this summer, as well as the procedures used by employees of outside contractors that are believed to have caused the leaks.