In a taped interview in Washington on CBS's "The Early Show," Rice said she remains convinced her upcoming trip to the Middle East with U.S. President George Bush will push the process forward. The trip begins Tuesday.
"Well, if the parties want to do this and will put the energy and the will into it, I think they can do it (reach a peace agreement)," Rice said.
She added: "A conflict like this has gone on for decades. It would have been resolved had it been easy. It would have been resolved a long time ago. We've been close a couple times; couldn't get it done.
"But I'm also a big believer that nothing's really impossible. It might be improbable but it's not impossible."
Bush will meet with the leaders of Israel, Saudi Arabia and Egypt during his five-day trip, the second by Bush to the region this year.