NASA's top priorities are a replacement for the space shuttle and completing the international space station, and some other programs are being cut or deferred to concentrate the agency's resources, NASA Administrator Michael D. Griffin (search) said Thursday.

"NASA cannot afford to do everything on its plate today," he told the House Science Committee. Funding priorities required the agency to cancel several programs that "we either did not need or did not need right now," Griffin said.

For example, it seemed like putting the cart before the horse to continue life science studies about how people respond to being in space before the agency was sure it could put people back in space, he said.

In addition to life sciences, another affected program is nuclear systems technology, Griffin said.

That program is designed to provide power to an outpost planned for the surface of the moon. But that won't be needed until after 2018, so the work is currently being deferred, he said.

The agency has adopted a "go-as-you-can-pay" approach, Griffin said.

That focus on two primary areas should serve as a warning of potential cuts for the rest of NASA, Rep. Bart Gordon (search), D-Tenn., commented.

Committee Chairman Sherwood Boehlert (search), R-N.Y., expressed support for Griffin but added that "NASA cannot use aeronautics and science as a piggy bank to fund human space flight."

Griffin said the next flight of the space shuttle is still planned for spring, adding that while the agency was surprised by problems with the foam insulation on the last flight, a lot has been learned from that.

NASA has been developing the new crew exploration vehicle, which is intended to fly to the moon but also can replace the space shuttle when it goes out of service.

Delaying that work could result in the United States being out of the manned spaceflight business for a few years after the shuttle is retired, at the same time other nations are increasing their space programs, Griffin said.

In addition, he said, NASA is encouraging private industry to submit proposals to carry cargo and crew to the space station.