NASA's administrator rejected a formal request by the accident board looking into the Columbia disaster to reassign top agency officials from participating in the investigation, the first serious dispute over the integrity of the probe since the space shuttle's breakup killed seven astronauts.

Administrator Sean O'Keefe, promised instead that over the next several days NASA will make changes so that professionals outside shuttle management lead cooperative efforts with the investigating board. O'Keefe said reassigning managers would be viewed as prejudging whether they were culpable in Columbia's loss, and he wrote, "I will not submit anyone to this treatment."

The investigating board, led by retired Adm. Harold Gehman, disclosed the correspondence on its Web site Saturday. A board spokeswoman, Laura Brown, said Gehman interpreted O'Keefe's promises as responsive to the board's concerns. The board's members, including Gehman, were appointed by O'Keefe to investigate incidents before Columbia came apart in the skies over the Southwest.

Gehman wrote to O'Keefe on Tuesday asking him to remove top shuttle managers from managing or supporting the board's investigation into the accident. "We believe it is in the best interest of these key people, NASA and the effective progress of the investigation if they were to be replaced by other knowledgeable people to manage the response and investigative support," Gehman wrote.

In a strongly worded response sent Friday, O'Keefe wrote that he feared reassigning shuttle managers "will be viewed as prejudging the facts before the investigation is complete," and that even replacements could suffer "the same appearance of conflict in the future."

"Simply reassigning personnel will not accomplish your goal," O'Keefe wrote.

O'Keefe's response drew criticism from Rep. Anthony Weiner, D-N.Y., a member of the House Science Committee, which has oversight responsibilities over NASA.

"If O'Keefe wanted to give the impression he was more interested in circling the wagons than exposing the truth, he's done everything this week to do that," Weiner said. "The more outsiders we have looking at this information without the interference or filter of what could be self-interested NASA employees, the better.

"Many Americans are concerned about having an information flow that is being directed at key points by the various people who may have been shown to have some responsibility for the accident or shown to have been decision-makers and not acting on subordinates' warnings," Weiner added.

Among others, Ronald Dittemore, the shuttle program manager, has appeared active in the search for the cause of Columbia's disaster in the weeks since its breakup on Feb. 1. In an internal message sent to a colleague Feb. 11, Dittemore sought copies of e-mails among senior engineers expressing concerns about the safety of the shuttle during the mission.

O'Keefe did promise changes the board accepted, saying that NASA's task force will be changed over the next several days to assist the board in its investigation, and that the agency's group will be led by people not associated with management of the shuttle program.

"It is apparent that our original structure to support the investigation needs to transition," O'Keefe said.

Some members of Congress have expressed misgivings about a lack of independence of the investigation board and have urged President Bush to appoint a commission, following the pattern set by President Reagan to investigate the Challenger explosion in 1986.

In response, NASA and the board several times have changed the rules by which the board operates. Among those changes, deadlines were removed for the board's final report, new members were added to the board and the board was instructed to publicly release its findings. Under earlier rules, the board was to have provided its final report directly to NASA within 60 days.