Biden said he was convinced the group could come up with an agreement that increases the so-called debt limit and makes significant headway on President Obama's promise to cut the deficit by $4 trillion over the next decade or so.
"It ain't over till it's over," Biden said, "but I'm convinced we can come up with an agreement that gets the debt limit passed and makes some real serious down payment on the commitment for 4 trillion bucks over the next 10 or 12 years."
At the same time, however, Biden's Democratic allies in the Senate vowed that any deal this summer to cut the deficit won't cut back benefits for people enrolled in Medicare.
"We will not allow cuts to seniors' benefits," said Sen. Charles E. Schumer (D., N.Y.).
The Biden-led talks are aimed at producing an agreement that would pass in concert with an increase in the nation's $14.3 trillion debt limit. Republicans want a borrowing increase - and a commensurate level of cuts - that would provide enough borrowing room so that there would need to be only one vote on the politically toxic topic before next year's elections.
"You hate to have to come back and do it in pieces," said Sen. Jon Kyl of Arizona, who is representing Senate Republicans in the talks.
Federal Reserve Chairman Ben S. Bernanke on Tuesday urged Republicans to support raising the borrowing limit. He said that threatening to block the increase to gain deeper federal spending cuts could backfire and worsen the economy.
Even a short delay in making payments on the nation's debt would cause severe disruptions in financial markets, damage the dollar, and raise serious doubts about the nation's creditworthiness, Bernanke said.