Diverting money from the orbiting research outpost to President Bush's goal of sending astronauts back to the moon and eventually on to Mars is preventing some scientific experiments on the space station, Glenn told an audience of about 300 high school students and space enthusiasts at the COSI Columbus science center.
"To not utilize that station the way I think it ought to be utilized is just wrong," said Glenn, 85, also a former U.S. senator.
Glenn made three trips around the planet inside his Friendship 7 capsule on Feb. 20, 1962, making him a national hero and proving that the nascent NASA space program was competitive with the Soviet Union, which had accomplished a manned orbital flight a year earlier.
In 1998, Glenn, then 77, flew on the shuttle Discovery and became the oldest person ever in space.
He said he supports the president's moon and Mars goals but not at the expense of the space station, which is only two-thirds complete.
NASA and its international partners, including Canada, Japan and Russia, hope to finish the space station in 2010, but no decision has been made to extend its operation past 2016.
Glenn, a Democrat who represented Ohio from 1975 to 1999, said the station shouldn't be abandoned, especially after costing taxpayers billions of dollars.
"We will not even begin to realize its potential," he said.
A White House spokesman said Tuesday night that officials were not prepared to comment. Messages were left after business hours at NASA headquarters."