There is a small chance that the space shuttle Atlantis, grounded 2 1/2 weeks ago by a leak in its fuel system, could be repaired on the pad and launched as early as Aug. 10, a NASA official said yesterday.

"We're going back to flight," William Lenoir, the agency's associate administrator for space flight, said at a news conference.

But Lenoir also said he is skeptical that Atlantis will be ready by then, because the system may be leaking for reasons too complex to be fixed on the launch pad. If so, the shuttle and its fuel tank will have to be taken back to the hangar and the defective fuel line will have to be dismantled.

"In all honesty we do not expect what we can do on the pad {to be enough} to fix the problem," he said.

The leak is in a 17-inch diameter pipe that carries supercold liquid hydrogen from the external tank to the orbiter's main engines. The pipe is in two halves that must disconnect in flight when the empty tank is jettisoned. Lenoir said NASA workers will inspect the bolts and welding on the pipe's flange, the part that was leaking, in the next few days. They plan to retest the system for leaks on July 25, after making whatever repairs are possible on the pad. If the shuttle passes the test, it will probably be launched between Aug. 10 and 12.

The shuttle Columbia, which was scheduled to lift off in May but was grounded after a different type of fuel leak was detected, is now set to take off between Sept. 10 and 15. NASA officials say they are confident Columbia is ready for liftoff because the part of its fuel supply system that was leaking was replaced with hardware from the shuttle Endeavour, which is still under construction, that passed a leakage test earlier this year.

But if the quick repairs don't fix Atlantis's leak, its launch would have to be delayed until after the Oct. 5 liftoff of Discovery, carrying the Ulysses spacecraft on a mission to study the sun. Columbia would still be launched in early September.

If Atlantis passes the test, "that sequence of events would permit two flights before Ulysses," Lenoir said. "It requires us to be lucky twice. In the first case, it requires what we intend to do to fix it on the pad to work. And it requires that we not be unlucky with unforeseen work on either Atlantis or Columbia and that we not see an excessive amount of bad weather on the pad."

"While we consider it unlikely, we want to see if it works," he added.

NASA officials announced last Friday that the leak in Atlantis's fuel system was unrelated to the one in Columbia's fuel system. While the leak on Atlantis was traced to the flange, the one on Columbia is in either of two small seals in a shaft entering the pipe.

Lenoir said he doesn't anticipate a leak in Discovery's fuel-supply system, since the Atlantis and Columbia leaks are unrelated. "We do not have a generic problem," he said.

Much of the schedule juggling is intended to protect the Ulysses launch date. The scientific spacecraft can only be launched during a brief "window" in October because the planets must be aligned in a certain configuration for its mission to work. If Ulysses is not launched in October, NASA would have to wait more than a year before trying again.

At another news conference yesterday, President Bush said he had "great confidence" in NASA Administrator Richard H. Truly, who has come under fire recently for the problems with the shuttle and the Hubble Space Telescope. On Monday, the White House ordered an outside review of the space agency.

"It's such a complex organization that it is appropriate that the administrator now call on the best minds he can find to see how we're going to meet these goals," Bush said.

NASA also announced formation of a 10-member panel of optics experts to work on ways of improving the images sent to Earth by the $1.6 billion telescope.

Staff writer Ann Devroy contributed to this report.