Washington wants to place a radar station in the Czech Republic as part of a missile-defense system it says is aimed at countering potential threats from countries like Iran.
But polls show some two-thirds of Czechs oppose the plan.
In an interview today with RFE/RL, Klaus said that was in part because people did not feel a clear enough threat.
"I think this opposition should be respected," Klaus said. "It is real. No one has invented it. No one is faking the polls that are being taken. So the first point is that this is the reality."
The plans have prompted strong opposition from Moscow, which has described them as a threat to Russia.
AN RFE/RL VIDEO PRESENTATION: The Czech Republic responds to the U.S. missile-defense proposal.