"In all my years of my involvement," Blomberg testified, "I have never been as worried for space shuttle safety as I am right now. All of my instincts suggest that the current approach is planting the seeds for future danger."

Bush released yesterday his proposed 2004 budget that would provide $15.5 billion for NASA, a $500 million increase - or about 3 percent - over what he asked for in 2003. The budget, completed before Saturday's catastrophe, includes a $600 million boost for the shuttle program.

"NASA's budget numbers are now entirely meaningless. There's going to have to be a major re-examination of all those numbers," said Heidi Tringe, a spokeswoman for the House Science Committee.

Mitchell E. Daniels Jr., Bush's budget director, said it is too early to say whether the Columbia disaster will affect NASA's funding. Bush has increased the agency's budget since taking office, Daniels said, and there is no guarantee that more funding would improve safety or prevent disasters.

"If there's a lesson in the last couple days, it's, I suppose, another sad example that more money alone can't always avoid very sad setbacks," Daniels told reporters yesterday.

The administration's budget documents, meanwhile, contained some criticism of NASA: "Shuttle operations are well managed but investments to improve the shuttle suffer from inadequate planning and poor cost management."

Congress has not completed negotiations on the budget for the current fiscal year. Nelson said Congress should include at least "a few tens of millions" for shuttle upgrades as part of a midyear supplemental spending measure it is expected to pass this spring. Daniels suggested that is unlikely.

One issue lawmakers are certain to probe is NASA's response to evidence it found shortly after liftoff showing that a piece of insulating foam had fallen from Columbia's big external fuel tank, hitting the orbiter and possibly damaging thermal tiles on its left wing. The problem had occurred before on other missions, NASA has said.

"One of the first things we need to ask is, if it did happen before, how could it possibly have happened again?" Rohrabacher said.

The Senate unanimously passed a resolution yesterday to honor the shuttle mission, saying it "commemorates, with deep sorrow and regret, the fate of the Columbia."