The National Aeronautics and Space Administration, long the most exotic and glamorous of federal bureaucracies, is deep in painful soul-searching about how, and why, the 25th launch of a space shuttle ended in fiery death and destruction.

The self-appraisal at NASA has been etched sharply into the national consciousness by the finding of a presidential commission investigating the Challenger explosion that the decision to launch the flight Jan. 28 "may have been flawed."

Tentative and carefully couched, that phrase has raised the most painful and disturbing question of all: Was the disaster a result of blind chance, or could the lives of the seven astronauts have been spared if men and women on the ground had done their jobs better?

The question is made more compelling by the presence aboard Challenger of Christa McAuliffe, 37, the New Hampshire school teacher who would have been the first of what NASA called "citizen passengers" to ride a shuttle.

Last night, a presidential commission member was at Cape Canaveral to investigate reports that unusually low temperatures had been recorded shortly before liftoff on a solid rocket booster thought to be at fault in the explosion.

The sense of anguish is unmistakable at NASA's white marble headquarters at the foot of the Capitol, where black crepe drapes displays of photographs of the crew and Challenger Flight 51L's colorful shoulder-patch emblem.

It was disclosed last week that, for at least three years, some senior NASA managers were troubled that the joints of the shuttle's massive, segmented solid rocket boosters were not being sealed properly on previous flights. Post-flight inspecions had shown that hot exhaust gases could penetrate the joint's rubberlike O-ring sealers, threatening a catastrophic rocket failure.

Since no provision is in place for the crew's escape while the SRBs blaze the craft toward orbit, the sealing problem was extremely grave. Yet, even as they sought a solution, NASA officials stepped up the pace of flights and began suggesting that the shuttle was about to be pronounced fully operational.

A burn-through of the right booster is thought to be the primary cause of the explosion that destroyed Challenger after 73 seconds of flight. Photographs released last week by NASA show a puff of black smoke emerging from the side of the booster at liftoff and, 58 seconds later, a jet of white-hot fire erupting near one of its joints.

The unpleasant implications of this coincidence were strengthened when the booster's manufacturer, Morton Thiokol Inc., reported that the O-ring sealers do not function well in temperatures below the low 40s and said that it initially recommended delaying the Challenger launch because of the unusual cold that morning at Cape Canaveral.

[CBS News, quoting anonymous sources, reported last night that Thiokol engineers, the night before liftoff, were unanimous in emphatically advising NASA not to launch.]

The space agency seems headed for rough moments as the commission, headed by former secretary of state William P. Rogers, probes these questions.

At the same time, the ban announced Saturday by Rogers on participation in the inquiry by any NASA officials involved in the launch decision has left some agency professionals dismayed about the probe's long-term impact.

"Half the senior staff at Johnson [Space Center in Houston] is eligible for early retirement," said one veteran agency official. "I would think a lot of guys may be leaving very soon." Shuttle launches are controlled by Kennedy Space Center in Cape Canaveral and, as the craft clears the launch tower, mission control switches to Houston.

The commission has not singled out or named individuals and may never do so. Nor is there any suggestion that NASA has withheld information. "The cooperation from NASA is top-notch," said Dr. Eugene C. Covert, one of 13 commission members. But as a general principle, he said, "You shouldn't put somebody in charge of investigating themselves."

The commission's interest centers on learning which senior program directors and officials at several NASA space centers participated in flight-readiness conferences before the launch and what they did. The temperature near the pad was 38 degrees Fahrenheit, 13 degrees colder than during any previous launch involving the fleet of four $1.4 billion shuttles.

Intense preflight conferences begin several weeks before any launch and end with what is called the "L-minus-one-day conference," the day before liftoff. If the launch is approved at that time, workers begin "tanking" -- filling the shuttle's massive external fuel tank with liquid hydrogen and liquid oxygen.

Power generated by that tank is crucial because the two SRBs provide only 71 percent of thrust at liftoff. The external tank and both boosters are cut free of the shuttle before it enters orbit.

Once "tanking" occurs, the shuttle is so dangerous that at launch, the only humans within three miles of the pad are those strapped into the orbiter. This danger and the pressure of coordinating computer hardware and software in the most complex machine ever flown transforms the decision-making process into a tense blur of orders until the split-second before ignition.

Covert, a Massachusetts Institute of Technology physicist who helped design the shuttle's main engines, said the commission heard during closed sessions last week with Kennedy Space Center officials at Cape Canaveral "differing descriptions of the situation" preceding Challenger's liftoff.

These preparations unfolded as NASA attempted the second of 15 shuttle flights scheduled this year. Delays in early January involving the shuttle Columbia were so disruptive that the usual five-day-a-week teleconferences of senior officials at Houston, Cape Canaveral, Hunstville, Ala., and NASA headquarters were increased to seven days a week. Workers preparing shuttles at the Cape frequently put in 70- and 80-hour weeks.

The agency's outside safety board, established after the 1967 Apollo capsule fire, had warned repeatedly of dangers in moving from a more leisurely research schedule on the shuttle to the "operational" schedule envisioned by NASA.

The agency is also faced with high-level reshuffling as Dr. William R. Graham moves to consolidate his grip on NASA after barely two months as acting administrator. Some senior agency staffers have said Graham may have responded tardily to in-house suggestions that NASA appoint a Challenger board of inquiry headed by an outsider.

After previous mishaps, NASA had used such in-house boards. Some NASA veterans said they had hoped this would be true with the Challenger inquiry.

Groping for explanations and guidance, NASA's rocketeers have ruefully recalled the agency's watchwords during countdowns preceding the Apollo moon missions: "When in doubt, don't."