Six waivers specifically allowing space shuttles to fly despite unsolved problems with faulty rocket joints were nothing more than a routine way to ensure problems were being addressed, according to the person who signed those waivers, NASA official Lawrence B. Mulloy.

The waivers were the focus of a closed meeting Friday of the presidential commission investigating the Jan. 28 Challenger disaster. Commissioners apparently only recently learned of the waivers. A source said they were concerned about them, viewing them as another example of a "flawed" process at the agency that led to the launch.

A failure of a joint on the right solid-rocket booster has been identified as the primary cause of the destruction of Challenger and the death of its crew.

Mulloy, head of NASA's solid-rocket booster program at the Marshall Space Flight Center in Huntsville, Ala., said the waivers were nothing more than an acknowledgment that a problem existed and needed to be fixed. The waiver process specifically required that before each of six launches after July 1985, engineers had to justify continuing to fly despite the problem.

Mulloy, said in a telephone interview yesterday that he could have stopped shuttle launches -- by refusing to sign the waivers -- because of problems with leaky rocket joints, but that he and everyone else concerned thought the problem was being properly addressed and was not serious enough to suspend flights.

"A whole lot of people concurred in that decision to keep flying," Mulloy said.

He said the waivers were required when one joint on the booster -- the nozzle joint at the end of the rocket -- failed to seal completely during a flight in 1985. A task force was set up to resolve the nozzle joint problem, and until changes were made, the nozzle joint was designated a "launch constraint."

Before every flight, including the launch of Challenger, Mulloy was required to sign a waiver that supplied the reasoning behind continuing to fly despite the problem. He said the waiver process provided an opportunity for various internal panels to review that reasoning as well as progress toward resolving the problem, before approving a launch.

"It's a tracking thing," Mulloy said. "When there is an open problem like that, that is unresolved, it requires the project manager to concur in the rationale for continuing to fly given that the problem is still open."

The nozzle joints are slightly different from joints for the upper portion of the rockets, but those joints were experiencing similar, though apparently less serious, problems.

Mulloy said commissioners questioned him, other NASA officials and representatives of Morton Thiokol Inc. "aggressively" about the waivers at Friday's session, the commission's last.

He said commissioners seemed surprised to learn of the documents, but he added that he didn't know why commissioners didn't learn of them earlier. Given the other information the commission had received that showed that NASA officials realized the joints were a problem, he said, the waivers have little significance.

"It was a new document that contained the same information" as previous documents, Mulloy said