Astronaut Sally Ride, a polite smile frozen on her face but her fingers drumming with agitation, threw questions like stilettos throughout the three days of hearings held this week by the presidential commission in- vestigating the explosion of the space shuttle Challenger.

Sometimes, smiling tightly, she shook her head in amazement at what she was hearing from NASA witnesses. Once or twice a response moved her and former astronaut Neil Armstrong to lean back in their chairs, on either side of panel chairman William P. Rogers, and look at each other with raised eyebrows.

In the probe of the first American deaths after liftoff, the first human being to step on the moon and the first American woman in space had became interrogators of the men who run the agency that put them up there. The astronauts, no less than the public, had held certain favorable assumptions about the methods behind two decades of space miracles.

But by the end of the week, those assumptions appeared to have crumbled, and NASA employes were braced for what one called "a major reorganization" under a new leader. Sources said former agency head James C. Fletcher was the front-runner for the post of administrator and was interviewed this week by White House chief of staff Donald T. Regan.

Longtime supporters of the National Aeronautics and Space Administration, on Capitol Hill and elsewhere, expressed shock and incredulity as the three days of hearings exposed, layer by layer, what Rogers called the "flawed" process that led up to the final, fatal launch decision on the morning of Jan. 28.

The Watergate-like televised spectacle produced by the commission featured an increasingly indignant Rogers, a former assistant district attorney and attorney general as well as a former secretary of state, who emerged with unexpected force in the prosecutorial role of Sam Ervin, repeatedly asking officials where they had left their "common sense."

The hearings were a study in contrasts between image and reality. Instead of the crisp "Go" or "No-Go," safety-first image NASA has long sustained, the hearings revealed decision-makers who spoke in muddy "rationales" that, as they traveled up or down the chain of command, were transformed as if in an old-fashioned parlor game of "gossip."

Thus, a statement the morning of the launch by Rocco A. Petrone, president of the shuttle division of Rockwell International Corp. and a top NASA manager during the Apollo moon shot days, that "we cannot recommend launching," passed through subordinates and came out, "Rockwell could not assure the safety of flight." NASA officials said they took this to be "a concern," not a recommendation against launch. (Rockwell's concern was that icicles up to four feet long that draped the launch pad structure might damage the Challenger's heat-resistent tiles, which prevent the orbiter from burning up during reentry.)

Such discussions led repeatedly to mistaken or, some suggested, expedient misinterpretation on possible life-and-death matters.

"This illustrates one of the things that obviously has to be corrected," Rogers said. "There are a lot of maybes. A lot of people have been voting 'Maybe' or 'I don't vote.' It would seem to me this decision-making process should require people to take stands and you should have a record on it. . . . "

Though NASA has prided itself on an open, "bubble-up" style of management, the commission repeatedly caught NASA officials, as well as top managers at contractor Morton Thiokol Inc., in a syndrome that became familiar to Americans through the Pentagon Papers revelations about the military bureaucracy during the Vietnam war: Mid-level personnel didn't tell higher-ups bad news.

The investigation opened in a completely different atmosphere early last month. Then, in the immediate aftermath of the disaster, some commission members seemed openly sympathetic to the space agency.

But this week, in a State Department auditorium, after bringing 56 manned missions back safely, the agency was on trial for the one that failed, and the relatively anonymous men who run it were confronting the light of public scrutiny.

The NASA "can-do" tradition of unflappability was personified in solid-rocket booster project manager Lawrence B. Mulloy and rocket engineer George B. Hardy, mid-level managers at Marshall Space Flight Center in Huntsville, Ala. Questioned for several hours on Wednesday morning, they appeared cool and confident. Moving through the lunch line at the State Department cafeteria, they chatted easily and met strangers' stares unflinchingly.

They have steadfastly denied that they pressured the solid-rocket boosters' contractor, Morton Thiokol, to change its initial recommendation against a launch that day, and that they had reversed NASA's traditional approach that demands proof that it is safe to fly, rather than proof that it is not.

Mulloy testified that he always challenges his engineers to support their recommendations, whatever they are, with logic. He said he found a lack of logic in Thiokol engineers' warnings that unusually cold temperatures at the Kennedy Space Center about launch time could threaten the crucial seals on the rocket boosters.

In contrast, Thiokol managers seemed shaken during their appearances.

Robert Lund, mild-mannered chief engineer for Thiokol, apparently did not fully appreciate Mulloy's Socratic approach. He first supported his engineers when they recommended against launch on the night before the scheduled liftoff. But he folded under what he considered pressure from Mulloy, and finally from his own boss, Thiokol vice president Joe C. Kilminster, who asked him to "take off your engineering hat and put on your management hat." In the end, he switched sides, joining Kilminster in overruling his own engineers and recommending a "Go."

Lund was the target of some of Rogers' most withering remarks. "Mr. Lund, how do you explain the fact that you seemed to change your mind when you changed your hat?" Rogers asked. Later, Rogers referred to Lund as "chicken."

Ride zeroed in on NASA officials' apparent departure from "the book," asking repeatedly how officials could sit around late on the night before a launch debating the engineers' warnings about the effects of cold on the seals when NASA's rules, she thought, clearly labeled the rocket booster seal a "criticality 1." That means there is no backup system and if the item fails, the crew, vehicle and mission are lost.

No one had a satisfactory answer for the often-asked question: "Why not wait a day or two?"