WASHINGTON -- Three months after the Columbia disaster, NASA Chief Sean O'Keefe faced questions from Congress on Thursday about the U.S. space agency's "skimpy" budget and the shuttle program's future. "While we investigate Columbia, longer range issues must be addressed: the future of the shuttle and its successor, an aging workforce and an aging infrastructure," Sen. Barbara Mikulski told O'keefe at a senate appropriations panel hearing. "Unfortunately, the administration's budget does not do enough to address some of these long-term needs." Mikulski, a Maryland democrat, said in a statement that NASA's budget appeared "skimpy" after this year, and Sen. Richard Shelby, an Alabama Republican, said, "most of us believe that NASA is still vastly underfunded."

Both Mikulski and Shelby have NASA space flight centers in their states, Reuters reported.

"The ripple effect of this (Columbia) tragedy inevitably will impact the future funding of the manned space program as well as other missions in the space and earth sciences programs," said Sen. Kit bond, a Missouri republican.

The Bush administration's proposed NASA budget for fiscal 2004 is $15.47 billion, an amount submitted before the Columbia tragedy. Congress has provided a "down payment" of $50 million to respond to the Columbia aftermath, and expects those costs to rise as an independent investigation proceeds.

O'Keefe defended this budget proposal as "responsible, credible and compelling," even as he noted it was prepared before the Feb. 1 disintegration of shuttle Columbia over Texas. All seven astronauts aboard were killed.

The search for pieces of the doomed shuttle was complete, O'Keefe said, with the debris fields in Texas and Louisiana having been combed for more than 11 weeks. Remnants accounting for about 40 percent of the shuttle's weight have been recovered and are destined for a hangar at the Kennedy Space Center in Florida.

The independent Columbia accident investigation board confirmed on Thursday that some live worms from a bio-experiment that had flown on Columbia had been discovered in the wreckage.

But a spokeswoman for the board said they had come from the spacehab science module that rode in the orbiter's cargo bay, not in the crew compartment, as NASA had reported.

That means the worms and their survival are likely to have little bearing on the investigation. Some investigators had hoped their survival might point toward making such accidents more survivable for the crew.

NASA said the worms were discovered last Friday at the Kennedy Space Center, where the wreckage is being analyzed. They were not the same worms, known as C elegans, that flew on the shuttle, since they have a life expectancy of just a week to 10 days, but were descendants of Those Worms.

Even as the investigation board continued its work, O'Keefe stressed the need to return to human space flight, speaking earlier on Thursday at a traditional May 1 space day ceremony at the national air and space museum.

Addressing an audience of several hundred school children and their parents and teachers, O'Keefe noted that some 1,600 teachers had applied to fly in space as part of NASA's educator astronaut program, which is going forward even though the three-ship shuttle fleet remains grounded following the Columbia accident.

NASA planned to pick three to six teachers to join the astronaut program, O'Keefe said.