Treasury Secretary Tim Geithner said Sunday that he did not initially think lawmakers would bring the debt-ceiling negotiations "this close to the edge," appearing taken aback by the lingering distance between the two sides with an Aug. 2 deadline looming.

Geithner told "Fox News Sunday" that he remains confident lawmakers will lift the $14.3 trillion debt cap and avoid a national default.

"We're not going to end up there," he insisted. The treasury secretary, pressed repeatedly, would not explain what kinds of contingency plans might be in place in case Congress does not approve an increase by Aug. 2, saying there's "no other option" but to lift the cap.

At the same time, he warned that the negotiations have dragged on without a deal for far longer than he anticipated.

"We're running out of runway. We're almost at the edge. I never thought they would take it this close to the edge," Geithner said.

Though House Speaker John Boehner broke off talks with the White House late Friday, Geithner appeared to hold out hope for a large-scale deal -- such a deal, as envisioned, would raise the debt ceiling, while cutting spending and reforming the tax code and entitlements.

As a second option, Geithner pointed to a fallback plan in the Senate that would enact smaller cuts now and entrust a special committee to craft broader deficit reduction in the future.

Though Republicans have pressed for something short-term, Geithner said Sunday that a debt-ceiling increase that only brings the country into early 2012 "makes no sense."

He said the administration wants a deal that lasts "through the election."