Defaulting on its debt would be much more serious for the United States than any fiscal cliff or government shutdown, former Wells Fargo Chairman and CEO Dick Kovacevich said Monday.

"Obviously we have the resources to pay our bill, but we don't have the political will to do so, and that's just a tragedy," he said. "We just can't have a default. It would horrendous if we did."

On CNBC's "Fast Money," the Wells Fargo chairman emeritus said that the world's confidence would be shaken in the United States as the reserve currency if Congress failed to authorize payment on U.S. debt.

(Read more: Debt default damage already unfolding)

"Of course, default is much more serious than the fiscal cliffs we've had or the shutdown of the government," he said. "We just cannot let this happen."

Kovacevich said that the crisis was unprecedented.

"We've never had this before," he said. "If you really start getting into the details of this, you get very, very scared of what could happen."

Wells Fargo, whose third-quarter earnings beat Wall Street estimates, had seen declines in its mortgage business.

(Read more: Dark (but familiar) clouds float above earnings season)

Kovacevich said that an increase in interest rates would slow rising housing prices and lead fewer homeowners to refinance their mortgages.

"You're going to see housing prices either stop or stay steady," he said. "They may even fall in the future, and you're already seeing some incentives ... by new-home builders. If we can keep our economy reasonably strong, the purchase side of the mortgage side will still be good. We just won't have the refinances that we got in the past."

—By CNBC's Bruno J. Navarro. Follow him on Twitter @Bruno_J_Navarro.

—CNBC's Torrey Kleinman contributed reporting to this article.