Hours before his scheduled keynote at the Republican National Convention on Tuesday, New Jersey Gov. Chris Christie slammed a New York Post report that suggested he turned down an offer to be Mitt Romney's running mate because he doesn't think Romney can win.

"It's just complete garbage," Christie said on the "Today" show. "The two reporters who wrote the story know me and have my phone number, and neither one of them ever called me to ask me about the story, to verify or debunk it. They just wanted to put something good on the front page."

"I've been working hard for Mitt Romney for nearly a year, traveling to 15 states across the country," Christie continued. "I absolutely believe he can win and will win.''

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Beth Myers, who led Romney's search for a running mate, would not comment on the Post report during the Yahoo!/ABC News "Newsmakers" discussion at the convention on Tuesday.

Christie also downplayed the notion that his prime-time convention speech could be a stepping stone to his own presidential campaign.

"I think Mitt Romney will be at the next convention in 2016 being renominated for his second term,'' he said. "Then you're talking about 2020--that's long, long way away."

[Video: Chris Matthews accuses Romney, GOP of playing 'race card']

Christie defended Romney's decision not to release his tax returns and dismissed the controversy surrounding the Romneys' off-shore bank accounts, but added that he can't really relate.

"Here's the good news: I don't have enough money to send to tax havens, so I never had to confront that issue," Christie said. "I hope someday to have enough money to go to tax havens, but I don't now."

Matt Lauer also asked Christie about a joke Romney made last week ("no one's ever asked to see my birth certificate") which made light of the so-called "birther" controversy.

"I think if he had to do it over again, he wouldn't make the joke," Christie said. "But you know what, when you're on camera 12, 14 hours a day, and you're at a big rallies and you're just going off the cuff, there are going to be times you're going to say stuff you wish you could take back. Believe me, I could put together a catalog of things [I said] I wish I could take back."

He added: "If you get a chance to talk to Governor Romney, I think he'd tell you that he wishes he could take that one back."