WASHINGTON -- Top NASA officials who gave the go-ahead to launch the ill-fated Challenger mission were never told of a low temperature reading of 7 to 9 degrees on the shuttle's right booster rocket prior to liftoff, according to the space agency.

Jesse Moore, head of the space shuttle program and the top-ranking official involved in the launch decision, told a Senate hearing Tuesday that if he had known of the reading, "I would have asked more questions."

The temperature on the morning of the Jan. 28 launch has been a focus of a presidential commission's investigation into the shuttle accident because of concern that the cold might have affected the performance of critical O-ring seals between segments of the shuttle's two rocket boosters.

At the time of the launch the air temperature had risen to 38 degrees, but a dramatically lower temperature on the surface of the booster might have been an indication that supercold liquid hydrogen was leaking from the huge external fuel tank, investigators say.

Richard Feynman, a physicist on the presidential commission, said he does not believe the low temperature readings were caused by a cold hydrogen leak. In Wednesday's editions of the Washington Post, he said the readings could have been a result of breezes blowing past the cold external fuel tank onto the booster rocket.

The Post also said that, "at the urging of the National Aeronautics and Space Administration," officials of booster manufacturer Morton Thiokol agreed to the cold-weather launch on the eve of liftoff after twice recommending against it.

"Even at that point, however, a senior Thiokol official at Cape Canaveral refused to endorse the recommendation," the Post quoted an unidentified commission member as saying. "This shook us to the socks. We were unprepared for it. It changed the whole tone of the investigation."

The Post source said after hearing about that last week in a closed session at the launch site, "We threw everybody out of the room and decided we had to tell the president."

William Rogers, chairman of the presidential commission investigating the accident, called Donald T. Regan, the White House chief of staff, and said he was "appalled" to learn that key information about the shuttle's condition hadn't reached top NASA officials, according to the Post.

Moore told the space subcommittee of the Senate Commerce Committee that the reading was recorded on a hand-held infrared scanner used by workers examining the shuttle for ice contamination on the morning of the launch. No word of the low temperature reading was ever relayed to officials charged with deciding whether to go ahead with the launch, he said.

"Would that have caused you to have a material concern?" asked Sen. Donald Riegle (D-Mich).

"I believe I would have asked some more questions about what the reading indicated," Moore responded.

But Moore cautioned several times that the instruments making the low temperature readings are difficult to operate and he said the liklihood of error could be "quite substantial."

Nevertheless, several senators indicated concern about the breakdown in communications and asked Rogers whether such breakdowns had led him to conclude that the National Aeronautics and Space Administration's launch decision-making process was "flawed."

Rogers, however, would say only that the commission intends to elaborate on the "flawed" remark -- which was made last week -- at a future public meeting.

Even so, several senators suggested enough questions had been raised to cast a cloud over NASA's reputation for safety and efficiency.

"At this junction it seems to have been an avoidable accident, rather than an unavoidable one," said Sen. Ernest Hollings (D-S.C.).

Sen. Albert Gore Jr. (D-Tenn.), citing the low temperature reading and the space agency's long concern about the problems with the O-ring seals, declared, "Something has one wrong as far as NASA quality assurance."

While Rogers insisted that "it would be a mistake" to concentrate on any one possible cause, he said the right-side solidbooster pocket "appears to be the area where the trouble started."