Gates rejects Greenspan claim war is about oil

He conceded, however, that at this point backers do not have the two-thirds majority that would be needed to override a Bush veto of the legislation.

"But that doesn't mean we shouldn't fight for what we believe in just because the president may veto it," Levin said on CBS's "Face the Nation."

"I think there's enough Republicans who believe we've got to change course but whether they'll vote that way, we just simply don't know," Levin said.

(Additional reporting by David Wiessler, Mark Felsenthal and Doug Palmer)