President Bush vowed Monday that American astronauts would return to space, even as he expressed sadness at the loss of the space shuttle Columbia and its seven-astronaut crew.

"The seven brave men and women from the Columbia will be remembered for their achievements, their heroism and their sense of wonder. Our prayers are with their families and loved ones," Bush said at the National Institutes of Health where he was promoting Project BioShield, a program to speed up the distribution of drugs to combat bio-terror attacks.

"Their 16-day mission held the promise of answering scientific problems that elude us here on Earth," the president said.

Earlier in the day, Bush met with NASA Director Sean O'Keefe, who promised that his agency will look at every aspect of the space shuttle mission to determine what may have caused the disintegration of Columbia on its return to Earth last Saturday, the White House said Monday.

O'Keefe briefed the president on the chain of events that led up to the disaster and the ongoing nature of the investigation. He also made clear his intention to get back into space as fully as possible, said White House Press Secretary Ari Fleischer.  

But Fleischer said, "It's important to allow the independent panel, to allow the internal panel at NASA" to do the job of investigating the cause of the accident.

Fleischer said the president believes the independent panel and a NASA group investigating the shuttle disaster should be sufficient, and it was unlikely that the White House would conduct a separate probe. There is currently a "coordinated group" at the White House monitoring the various investigations.

"This country owes it to the people who lost their lives, to the families who were left behind and to the astronauts who stand ready to go on the next mission to make sure we explore" every potential contributor to the accident, said Fleischer.

O'Keefe's meeting with the president at the White House lasted 45 minutes. O'Keefe began by talking about the fallen astronauts' families and how their needs were being taken care of by NASA, Fleischer said.

Prior to his visit, O'Keefe said in a television interview that he planned to tell the president that NASA is doing everything possible "to secure the evidence" to determine what caused the accident and would "make corrections and get back to flight."

The president asked O'Keefe about the families and morale at NASA, Fleischer said.

The president and first lady will travel to Houston Tuesday to attend to a memorial service for the shuttle crew. They are expected to meet with family members of the lost astronauts.

Bush juggled his schedule Monday and Tuesday to make room for the meeting with O'Keefe and the memorial service. He scheduled for Monday night a meeting with the King of Bahrain.

On Monday, the president submitted his annual budget proposal to Congress, which called for a $469 million increase for NASA in 2004, up from its current funding of $15 billion. He also proposed increasing funding for the space shuttle $3.2 billion to $3.9 billion, a 23.9 percent increase.

The budget, which was prepared by White House budget director Mitch Daniels prior to the Columbia accident, proposed the increase because funding for the agency had been flat for the last decade, according to Fleischer. NASA had also suffered several delays in the development of reusable launch vehicles, which will require the shuttles to operate longer than planned, said Fleischer. Columbia was the oldest shuttle in service.

"Past management of shuttle investments suffered from unclear planning and cost overruns," the budget says. It calls on NASA to reform its shuttle investment and planning management.

"Inevitably, there will be a discussion out of this about how much NASA should be funded, should there be another orbiter built, and in fact, has it been so poorly funded in recent years that maybe, just maybe, it wasn't as safe as it should be?" Sen. Bill Nelson, D-Fla., who flew aboard Columbia in 1986 as a House member, said Monday.

Fleischer said that the president was making no conclusions about whether the funding decreases in the last had anything to do with the shuttle accident.

"It would be premature and unwise to make any judgments about that at this time," Fleischer said.

"It is a belief in the importance of the space shuttle mission," Fleischer said in explaining the increased funding. "The president is committed to the future of space exploration. He is committed to the astronauts" who are waiting on the ground as well as the nations that have contributed to the International Space Station.

"Having said that, I don't know if anyone can make any conclusions about funding at this point," Fleischer added.

The Associated Press contributed to this report.