A weekend accident that damaged a redesigned booster rocket may force yet another delay in the shuttle launch, now scheduled for early September.

But NASA and Morton Thiokol officers are still assessing the damage to the booster, which was scheduled to be tested July 25.Morton Thiokol spokesman Rocky Raab said the booster was damaged over the weekend when a worker mistakenly put too much pressure in its O-ring seals during a routine procedure.

"During leak test operations on the center field joint of the assembled test motor, the joint was inadvertently over-pressurized. Two pressurization lines were switched and 1,000 psi pressure was applied between the capture feature and the primary O-rings instead of 100 psi," Raab said.

"An examination inside the motor showed that bonded J-seal insulation had separated as a result of the over-pressure. Additional tests are being conducted to determine the condition of the joint."

Raab said the center joint of the motor was already deliberately flawed as part of the testing procedure.

He said a new test firing date can't be set until the examinations are complete, although officials believe the motor can be fired sometime before the end of August.

Completion of the test is critical in order for the Space Shuttle Discovery, now being readied for launch at the Kennedy Space Center, to fly. Discovery currently is mounted on it launch pad undergoing tests before a planned flight readiness firing of its three liquid-fueled main engines.

Discovery's launch will mark the first shuttle flight since an O-ring failure caused the Challenger to explode into a giant fireball in Jan. 28, 1986.

NASA managers scheduled a teleconference Monday afternoon to discuss the incident and its impact on the flight of Discovery. There is speculation the accident could delay Discovery's launch by as much as two weeks.

The trouble comes on the heels of another accident at Morton Thiokol's plant in recent weeks in which the test booster's nozzle steering mechanism was damaged when an engineer mistakenly applied high pressure to a low-pressure inlet in the hydraulic system.

The mistake ruptured a hydraulic accumulator, and as a result, engineers had to replace the booster's aft skirt, which houses the steering mechanism, with one used in an earlier booster test firing.