The White House and House of Representatives Speaker John Boehner have exchanged new proposals in "fiscal cliff" talks, congressional aides said on Tuesday, in a possible sign of progress ahead of the end-of-year deadline.

The exchange of at least some new details over the last two days came as private talks quickened in the effort to avert the automatic steep tax hikes and spending cuts set for January 1 unless Congress intervenes.

Economists have warned the fragile economy could slip back into recession without a deal.

Despite the new proposals, Republican Boehner repeated his call for President Barack Obama to offer more details on spending cuts to be included in any final deal.

"We're still waiting for the White House to identify what spending cuts the president is willing to make as part of the balanced approach that he promised the American people," Boehner said on the House floor after seeing the Obama offer.

The White House fired back that the administration had submitted extensive proposals to reduce spending but Republicans had not offered specifics on increasing revenues.

"There is a deal out there that's possible," White House spokesman Jay Carney told reporters. It could include reduced spending, more revenues and tax reform as long as Republicans accepted higher tax rates on the wealthiest Americans, he said.

"We do believe the parameters of a compromise are pretty clear," Carney said.

Obama and Boehner had previously exchanged opening proposals aimed at cutting deficits by more than $4 trillion over the next 10 years, but they differ on how to get there.

Obama and Democrats demand that tax rates rise for the wealthiest 2 percent of Americans. Republicans want existing lower rates continued for all brackets and prefer to raise more revenue by eliminating tax loopholes and reducing deductions.

Republicans also want deeper spending cuts than those sought by Obama and fellow Democrats, particularly on social entitlement programs like the government-funded Medicare and Medicaid healthcare plans.

Earlier on Tuesday, Boehner said: "I'm an optimist. I'm hopeful we can reach an agreement."

But Senate Democratic leader Harry Reid said it would be difficult to reach an agreement before Christmas.

"Until we hear something from Republicans, there's nothing to draft," Reid told reporters, referring to writing legislation based on a deal. "It's going to be extremely difficult to get it done before Christmas."

Boehner spokesman Michael Steel said the counteroffer from Boehner would achieve tax and entitlement reforms that would solve the looming debt crisis, but offered no more details

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