Glenn, the first American to orbit Earth and a former Ohio senator, said U.S. experiments in the low gravity of space have produced "some of the most unique, cutting-edge research in the history of the whole world."
The Bush administration has said future U.S. research projects on the station would focus on helping achieve its proposed moon and Mars missions.
Glenn said cutting back on the space station would be "breaking our promises to our own scientists ... and I think we're breaking our promises to the 15 nations" that are participating in the space station program.
Space station research has produced tangible results, including better medicines and more productive rice harvests, Glenn said. Eliminating that kind of research would enable other nations to fill the void and benefit from new technologies, the Democrat said.
"I just don't think that's right," he said, adding that space exploration and research go hand in hand. "I think you should do both. I don't think you cut out one to do the other."
The Dayton hearing at the U.S. Air Force Museum is the second of five being held around the country as the President's Commission on Moon, Mars and Beyond prepares a report to be presented to President Bush in June.
Glenn also questioned the wisdom of building up a moon base as a staging base for an expedition to Mars. That would take "dozens" of flights from Earth, and probably use up most of the money earmarked for the Mars trip.
"I hope we don't chew up all our money on the moon and never get to Mars," he said.
Earlier Thursday, Air Force generals told the commission the military plays an important role in U.S. space exploration and should continue to partner with NASA.
The generals defended the military's role in space exploration when commissioner Carleton Fiorina asked why the military is involved.
"Although we would like space to be a peaceful medium, the fact of the matter is history says that it may not always be that way," said Martin, commander of the Air Force Materiel Command. "We should be prepared for that."
The military helps conduct space-related research projects, and Gen. Gregory Martin said military equipment in space helps prevent conflicts on Earth. For example, military satellites can detect buildups of armies on the ground.
Lt. Gen. Dan Leaf of the Air Force Space Command said excluding the military from U.S. space efforts would decrease the chances of detecting and heading off conflicts on Earth and increase the likelihood that a U.S. response to an attack would be less precise and more destructive.
"That's in nobody's interest — not ours, not our adversaries," Leaf said. "We don't want to wage war in space. There is a peaceful place for the military to participate in space."