WASHINGTON -- NASA is seeking nearly half a billion dollars in its budget for next year to make safety upgrades on the space shuttle to ensure that the aging craft can meet the nation's piloted space needs for the foreseeable future.

The $488.8 million request is part of a $1.6 billion program to improve almost every major area of the space shuttle system by 2005. NASA also hopes to spend an additional $630 million to upgrade the checkout and launch control operations at the Kennedy Space Center, bringing the total tab for shuttle safety upgrades in the next five years to $2.2 billion.

With the 100th shuttle flight on the launch pad, NASA is looking to build on the several hundred key safety modifications that it put in place after the 1986 Challenger accident -- the agency's 25th shuttle mission. Those improvements include redesigning the twin solid-fuel rocket boosters and installing an emergency escape hatch for the flight crew.

The space agency has argued that additional upgrades between now and 2005 are necessary in order to fly the shuttle safely until at least 2012.

"Our priorities are upgrades that can reduce risk," said Elric McHenry, NASA's manager of space shuttle program development. "Our long-term goal is making spaceflight as safe as commercial aviation."

But it is far from clear what sort of spacecraft the nation will be flying if and when space travel should ever get that safe.

There is continuing debate in the halls of Congress and within NASA just how long the space shuttle -- now almost 20 years old -- should continue to fly.

One camp believes there is no reason the shuttle can't fly until 2030 with the appropriate upgrades.

The other, which includes Rep. Dana Rohrabacher (R-California), powerful chairman of the House space subcommittee, believes the shuttle should be replaced in 2010 with a next-generation reusable launch vehicle.

A milestone decision was to have come this year, when the X-33 was supposed to have been flown 15 test flights by 2000 to demonstrate the new technology. But the trouble-plagued X-33 is grounded indefinitely and NASA's proposed Space Launch Initiative -- a new attempt to encourage successor technology to the shuttle -- will not reach maturity until 2005.

The concern by some in the aerospace community and Congress is that all the shuttle upgrades may unwittingly confer an unfair advantage to the shuttle in the future direction of piloted spaceflight.

As planned, the last of those improvements for the shuttle would be in place by the time a national decision rolls around five years from now on a shuttle successor. Congress already has decided that the shuttle will be a contender, regardless of what shape it's in by then.

"Congress supports shuttle safety and some additional investments in the shuttle, but it also is interested in seeing that the mandates of the Commercial Space Act are carried out," said Jim Muncy, who heads a space consulting firm PoliSpace in Arlington, Virginia.

"It's very important that these upgrades are related to safety and not just things to reduce the cost of flying the shuttle. A lot of times those don't make sense," he said.