The space shuttle Challenger's solid rocket boosters were not examined by any NASA engineer in the 38 days it spent on the launch pad until liftoff Jan. 28, an official said today.

Thomas Utsman, deputy director of the Kennedy Space Center, said that although no previous shuttle sat through colder weather for a longer time, the National Aeronautics and Space Administration did not attempt to make a special structural inspection of the boosters, thought to have played a role in the craft's explosion.

"Once it is moved to the pad, it is considered a structurally safe vehicle," Utsman said in a briefing on quality control. "There are no more physical tests, to my knowledge."

Utsman also reported that the number of NASA quality control inspectors assigned to examine shuttle hardware has fallen from 59 at the end of 1983 to 48 now.

The briefing, first of its kind since the explosion, reflected a relaxation of NASA's policy of withholding information pending conclusion of the investigation of the accident. NASA also plans on Wednesday to release "several hundred pages" of documents relating to the shuttle's booster rockets, signaling a possible change in its decision to "impound" all engineering data relating to the flight.

Agency sources said the new approach demonstrated NASA's increasing concern that its reticence since the accident has contributed to negative news stories.

Although Utsman and other NASA officials said that it is not necessary to inspect a shuttle's solid rocket boosters while the craft sits on the pad and that the agency has never done so, a U.S. rocket expert said that unusual cold in Florida last month should have made engineers examine their assumptions.

"To leave it for that length of time at those temperatures ought to be a great concern," said Gary Flandro, a professor at the Georgia Institute of Technology. "It should have worried NASA."

The space agency released today a record of temperature at the Shuttle Landing Facility, about four miles from the launch pad.

It showed that the weather was far colder when Challenger lifted off than for any of the previous 24 shuttle flights. The average temperature at launch for those missions was 73 degrees, according to NASA. It was 38 degrees when Challenger lifted off.

In discussing the reduction of NASA quality control inspectors, Utsman said the shuttle's prime contractor, the Lockheed Space Operations Co., has increased the number of its quality control inspectors who examine flight hardware from 262 in 1983 to 295 now.

He said the change reflects a transfer of a certain amount of responsibility for inspection to the contractor. And he listed retirement and attrition as the main reasons for the decrease in NASA quality control officers.

Utsman also addressed reports that frequent overtime and fatigue among key technicians could have contributed to problems with the shuttle's quality control. "The overtime is higher than we would like it to be," he said, citing an average overtime rate among Lockheed employes of 15 percent, or 46 hours worked each week.

But he added that he did not think there "was a fatigue factor" that could have contributed to the Challenger explosion. "We don't run a sweat factory out here," he said.

A spokesman for Lockheed said that the overtime figures resulted from unusually heavy work schedules. "We'd like to get ourselves into a position where we could reduce the overtime," said John Williams, the Lockheed public affairs officer at here. "But when we have overtime, it is inevitable, and it is caused by the workload out there."

In another development today, CBS News showed tapes of shuttle launches in November 1985 and August 1984 in which unusual plumes appeared to be coming from the crafts' solid rocket boosters.

A plume from Challenger's right booster is being investigated in connection with its explosion.

CBS said NASA was examining similar tapes. An agency spokesman said tonight that both of the earlier launches were normal.