Cheney looked over the Democratic field of potential candidates in an interview with conservative talk show host Sean Hannity.
"I think Hillary Clinton is a formidable candidate," Cheney said. "I think she could win. I hope she doesn't. I disagree with her on nearly all the issues, but nobody should underestimate her. She's a very serious candidate for president."
Cheney said Obama, an Illinois Democrat and son of a Kenyan father, was an "attractive guy. Don't know him well, met him a few times. I think at this stage, my initial take on him was, he's been two years as a senator. I think people might want a little more experience than that, given the nature of the times we live in. But certainly, he's an attractive candidate. If he decides to run, he'll be a player on the Democratic side."
Obama said Sunday he hadin 2008, backing off previous statements that he would not do so.
As for himself, Cheney said he would not budge from his often-stated decision that he will not run for president. "It's firm, final, fixed, irrevocable," the vice president said. "I don't know how else I can say it. If nominated, I will not run; if elected, I will not serve."
Cheney also said he was optimistic about Republican hopes in congressional elections on Nov. 7.
"I think we'll hold both the House and the Senate," he said. Last week, Cheney raised eyebrows when he sounded less sure about GOP prospects. "I think we'll hold the Senate, and I also think we got a good shot at holding the House," he told Rush Limbaugh.
Karl Rove, President Bush's chief political strategist, dismissed national polls and argued that based on individual polls Republicans will hold onto the House and Senate. He made the comments in an interview with National Public Radio's "All Things Considered."
"I think Iraq and the economy play a role in virtually every race. But there are also local considerations in the local contest between two individuals that at the end of the day matters for great deal of the contest," Rove said.