WASHINGTON -- NASA Administrator Sean O'Keefe had been planning to return to Washington by Monday afternoon to brief reporters on the first NASA budget request assembled on his watch.

The briefing was canceled Saturday afternoon in wake of the worst human tragedy to befall NASA since the 1986 loss of the Space Shuttle Challenger. NASA still intends to send its 2004 budget request to Congress and release copies to the public on Monday, but without the usual fanfare and officials briefings, agency officials said Saturday.

NASA spokeswoman Sarah Keegan said the agency's 2004 request will be released at 3 p.m. Monday but that no media briefings are planned at this time. The budget documents will be posted on NASA's World Wide Web site. She said it is too early to say how or if NASA might modify its request in light of Saturday's accident.

In the request, NASA is expected to ask Congress to fund several new initiatives, including Project Prometheus, an accelerated nuclear effort to develop nuclear propulsion system for interplanetary travel and advanced nuclear power sources to provide power for robotic spacecraft. But that and other new initiatives are part of a budget that was developed under significantly different circumstances than NASA now faces.

NASA officials said in late 2002 that the agency planned to increase the shuttle flight rate to five missions per year. Funds supporting that level of flight activity are expected to be included in NASAs 2004 request to Congress.

But with NASA calling a halt to preparations for the planned March 1 shuttle mission to the international space station, it is unclear whether the agency will conduct another shuttle mission in 2003 year. How that would effect NASAs 2004 request, or the agencys 2003 budget, is not yet known.

NASA continues to operate under funding levels established for 2002. NASAs 2003 budget, like the budgets of most federal government agencies, is currently tied up in a $400 billion omnibus bill that the U.S. Senate recently sent to the House of Representatives.

Brian Chase, executive director of the National Space Society and a former congressional staffer, said NASAs decision to cancel the formal unveiling of its 2004 budget plan is to be expected.

"They obviously dont want to draw too much attention to the budget as it is because they know its going to change," he said.

Chase said he would expect NASA to continue its investment in space shuttle upgrades, perhaps accelerating the timetable for implementing those upgrades geared toward improving the overall reliability and safety of the vehicle.

At the same time, he said he would not be surprised to see NASA accelerate its investment in the Orbital Space Plane and other launch technologies that could help NASA recover the capability lost with Columbia.

Under NASAs amended 2003 budget plans, the agency intended to spend $2 billion over the next five years alone in order to field an Orbital Space Plane for crew return by 2010.

While the investigation "wont be cheap" Chase said he does not expect it to be a budget buster either. Whether the investigation identifies needs for costly changes to the three remaining orbiters is too early to say, he said.

Chase said he expects NASA will spend one to three months absorbing the implications of the loss of Columbia and submit any changes called amendment to its 2004 request late spring or early summer.

But he said he would "be surprised if NASA fundamentally changes the nature of its request" or abandons its new ambitions.

"I think in fact you may see a major push to see that those programs [like Prometheus] are preserved in the budget," he said. "Those programs really encapsulate the vision we have for the space program."

A current congressional staffer said that while NASA's new initiatives won't be treated as "dead on arrival," they will have to be scrutinized in light of present circumstances.

"Human spaceflight is the crown jewel of NASA and its on hold right now," the staffer said. "Any other new initiatives are going to take a back seat to assessing the problem we have and remedying it."

But as far as postponing the release of NASA's 2004 request, the Staffer said that is not really an option.

"It's not just NASA's budget that's coming out Monday, it's the President's request for the entire government," the staffer said.

That massive document was sent to the Government Printing Office more than a week ago, the staffer said.