WASHINGTON -- NASA's top administrator, Sean O'Keefe, said Friday he rejects the idea that nothing could have been done in orbit to help the crippled space shuttle Columbia and possibly save its seven astronauts.

Raising his voice, O'Keefe told reporters that NASA has a long history of responding to orbital emergencies and would have done so again had it been clear that Columbia was in trouble.

"To suggest that we would have done nothing is fallacious," O'Keefe said. "If there had been a clear indication, there would have been no end to the efforts."

O'Keefe was responding to a questioner who cited statements by shuttle program director Ron Dittemore that nothing could have been done to help Columbia and its crew even if Mission Control had been certain that thermal protection tiles on the space shuttle had been damaged.

One theory of the cause of the accident is that tiles damaged during launch allowed the superheated gases of re-entry to penetrate and destroy the hollow wing.

"I completely reject the proposition that nothing could have been done," O'Keefe said.

In remarks at a news conference on Feb. 1, the day of the Columbia disaster, Dittemore said that there was no way to minimize the torrid heat of re-entry in order to allow for missing or damaged tiles.

"And so once you get to orbit, you're there, and you have your tile insulation, and that's all you have for protection on the way home from the extreme thermal heat heating during re-entry," Dittemore said.

But O'Keefe heatedly dismissed on Friday the notion of doing nothing.

"I reject the premise that there was nothing that could have been done on orbit," said the administrator.

O'Keefe cited the response of Mission Control engineers to the Apollo 13 accident in 1970. Engineers devised a way for that mission's three astronauts to return safely to Earth after an oxygen tank exploded while the spacecraft was on its way to the moon.

The administrator acknowledged, however, that he knew of no formal plan that would have covered the case of Columbia, in which a space shuttle in orbit was suspected to have damaged thermal protection tiles, but there was no certainty of such damage.

He said trying to investigate the tiles using ground-based Department of Defense cameras was rejected because past efforts by the cameras had not produced useful images for objects as small as the tiles on Columbia's underside.

Columbia broke up during the final minutes of re-entry, killing all seven of the astronauts. Engineers have said sensors in the shuttle's left wing suggest that broken or damaged heat protection tiles allowed the 2,500-degree plasmas of re-entry to penetrate the wing's interior. Films of the shuttle's launch show insulation peeling from the craft's external tank and smashing into tiles on the underside of the left wing.

Meanwhile, retired Adm. Harold Gehman, head of the Columbia Accident Investigation Board, sent a letter to NASA expressing misgivings that NASA employees were participating too closely in the independent investigation, according to board spokeswoman Laura Brown.

Some Democratic members of Congress have expressed concern about the independence of the investigation board and have urged that a Presidential commission be appointed to replace the board. That would follow the pattern used by President Reagan to investigate the Challenger explosion in 1986.

O'Keefe insists the board is independent of influence by the space agency, and NASA personnel are cooperating fully.

Some Republican lawmakers have quoted Gehman as saying the board is "completely independent and will remain so."

In Friday's meeting with reporters, O'Keefe and William Readdy, NASA's chief of spaceflight, continued to defend how NASA dealt with an internal debate among engineers worried that the broken tiles could spell disaster for Columbia. E-mails released this week show that some engineers feared that the crew and the spacecraft could be destroyed if heat inside the wing damaged the left landing gear and its tires.

O'Keefe said he found the spirited discussion among the engineers extremely reassuring, and he would worry if there had been complacency.

"An absence of any debate would have been disconcerting," he said.

The debate never reached the highest levels of NASA, but O'Keefe said the best way to handle complex engineering questions was to let lower-level experts decide.

Calling himself the "most incompetent person" to handle such technological issues, O'Keefe said he preferred to allow people lower in management take responsibility for evaluating engineering risks and to make decisions.

"People then feel responsible at every level," he said. "I don't think you want to mess with that."

Even if he had been told of the debate among engineers, Readdy said, "I don't think that it would have affected the outcome."

Readdy said he would have consulted with Dittemore and probably have learned of the opinion of Mission Control engineers that the broken tile did not represent a catastrophic threat to the shuttle or its crew.

O'Keefe said he was pleased that the e-mails showed such a spirited debate among the engineers, but he worried that making the messages public may cause the engineers in the future to be more careful in what they say and less vigorous in their opinions.

"That is a concern," he said.

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On the Net: NASA on Columbia: www.ksc.nasa.gov/columbia/