Lawrence Mulloy, the NASA official most criticized for his role in the Challenger space shuttle tragedy, told agitated House committee members yesterday that, "in hindsight," the launch decision grew out of a misguided "group think" that relied on inadequate data in accepting what turned out to be an unnacceptable risk.

The appearance by Mulloy and other NASA officials from Marshall Space Flight Center was the first in public since the release nine days ago of a report by the presidential commission that investigated the Challenger disaster.

The report blamed the Jan. 28 accident on failure of a joint in a solid rocket booster developed under the supervision of the Marshall center in Huntsville, Ala.

The hearings before the House Science and Technology Committee were part of a continuing flurry of congressional activity related to the crippled space program as members of Congress grope for direction on the issue.

Sen. Jim Sasser (D-Tenn.) urged the Defense Department yesterday to abandon plans to launch shuttles from its newly built launch pad at Vandenberg Air Force Base in California and rely on unmanned rockets instead.

According to a congressional report, the Vandenberg pad is poorly designed because the shuttle's main-engine exhaust ducts "could fill with hydrogen gas and result in a detonation during launch."

Sasser also asked congressional investigators to determine whether a fourth orbiter to replace Challenger should be considered unnecessary if Vandenberg is shut down.

Meanwhile, in a Senate subcommittee hearing, some panel members continued to criticize the presidential commission for not placing individual blame for the shuttle disaster more directly.

NASA Administrator James C. Fletcher told the science, technology and space subcommittee that agency officials responsible for the tragedy "have been removed from the chain of command and they will be disciplined in accordance with the procedures that we always follow . . . . I think that's about as far as the civil service allows us to go."

Fletcher also said the National Aeronautics and Space Administration has decided to comply with the commission's recommendation that it create a powerful safety office, independent of the rest of the agency, to report directly to him.

During several hours in which House panel members retraced the commission investigation, Mulloy, head held high, more than once referred members to the opening passage in the report's chapter titled "An Accident Rooted in History."

It stated that the fatal problem "began with the faulty design of the joint and increased as both NASA and contractor management first failed to recognize it as a problem, then failed to fix it and finally treated it as an acceptable flight risk."

Responding to criticism of Marshall's tendency to withhold vital information from top shuttle program officials, Mulloy and Marshall director William Lucas told the panel they felt that they had repeatedly informed higher levels of NASA management of concern about the joints.

William R. Graham, acting NASA administrator at the time of the accident, told the panel that, although Marshall could have presented the matter more forcefully, "it's unfair to focus all the criticism on Marshall . . . . The problem lies in more than one location."

Graham said NASA is conducting a "review" to find out which top agency officials attended readiness reviews at which Marshall officials discussed the joint problems.

Earlier, Allan McDonald, the engineer for booster contractor Morton Thiokol Inc. who warned against launching Challenger in such cold weather, testified that NASA's written specifications for the boosters failed to state clearly in what weather the shuttle should be able to fly.

After repeated questioning on conflicts between NASA and Thiokol about what the specifications called for, McDonald said, "I think the specification for this motor is a lousy one."

Joe C. Kilminster, one of the Thiokol vice presidents who overruled their engineers' recommendation against launching, told the panel:

"Obviously we were wrong. We did not have the safety margin necessary to cover some things we were not aware of," such as the low temperatures.

"In hindsight, we all wish we could reverse the judgment . . . . The decision we made that night has been constantly on my mind since the morning of Jan. 28th."