Washington ? NASA’s top official said Thursday that engineers’ dire speculations while Columbia was still in orbit were evaluated at the proper level below top management but that the space agency would review the decision-making process.

Speaking before the House Science Committee, Sean O’Keefe, administrator of the space agency, vigorously defended the way NASA dealt with a flurry of e-mails among engineers about the possible destruction of Columbia during its return to Earth. He said experts considered the issues and decided the space shuttle would be safe.

O’Keefe also announced that because the Columbia accident forced grounding of the space shuttle fleet, Russian spacecraft would be used to exchange crew members aboard the International Space Station.

A debate among engineers about the risks Columbia faced during its re-entry never reached top NASA officials, but O’Keefe said the space agency management system expected lower-level experts to evaluate risks and make decisions about mission operations.

“I certainly am not privy to every single one of those deliberations that go on across an agency of 18,000 people and another 100,000 folks who engage in launch operations and the continued activities of the agency,” O’Keefe said in a heated exchange with Rep. Anthony Weiner, D-N.Y.

Weiner, who apologized at one point for getting “hot under the collar,” said it was “stunning” that serious safety concerns were never shared with NASA’s top management. He said it should be O’Keefe’s priority to keep up with discussions of space shuttle safety although the administrator learned of the debate among the engineers only when NASA released the e-mails Wednesday.

“Why was it that even if there was hint of a footnote of a memo on a scrap of an envelope that was within this investigation’s scope, that it only made its way to you yesterday, at the same time it made its way to everyone else?” Weiner asked.

“It looks like that dialogue went on at exactly the right level,” O’Keefe responded. He said senior engineers made the decision. How NASA handles such engineering decisions, among other issues, will be considered by the Columbia Accident Investigation Board, he said.