NASA discovered a fuel-line crack in its newest space shuttle Wednesday, the same potentially dangerous problem affecting the rest of the fleet.

The small crack was found in the metal liner of a hydrogen-fuel line inside Endeavour, which returned from orbit just last month. Similar cracks have been found in the same parts on the three other shuttles, Atlantis, Discovery and Columbia.

Engineers are still inspecting Endeavour, which first flew in 1992, and more cracks are anticipated.

"We've got it on the other three, so we're not necessarily surprised to see that Endeavour has cracks, too," said NASA spokesman Bruce Buckingham.

Buckingham said there is no way to know, with certainty, when or how the cracks occurred. "But I think a reasonable person can assume we've been flying with these cracks," he added.

The problem was first detected three weeks ago on Atlantis. Inspections quickly turned up cracks on Discovery and then Columbia. The work on Endeavour had to wait until the shuttle returned from Edwards Air Force Base in California, where it landed June 19 following a space station visit.

Columbia's science research flight with the first Israeli astronaut, which had been scheduled for a July 19 liftoff, is on indefinite hold. The launch dates of all other shuttle flights this year are also in question.

The concern is not that the 12-inch-diameter fuel lines might leak, but that the cracks might grow and that metal chips might break off and end up in an engine. That could lead to an engine shutdown during launch, with possibly catastrophic results.

The cracks are up to three-tenths of an inch in length and are located in liners used to direct the flow of hydrogen fuel to the main engines.

Buckingham said NASA does not consider the shuttle fleet grounded — at least not yet. There is a possibility that engineers may conclude that the spaceships can fly safely with the cracks and that no repairs are needed, he said. But if the cracked liners need to be replaced, it could take months to manufacture new parts.

Seven engineering teams, involving workers around the country, are working practically nonstop to determine the severity of the problem and devise possible ways to fix it.

Despite the problem, NASA is still working toward a late August launch of Atlantis and an October launch of Endeavour. Both are space station missions.