Let the endgames begin.

After a Christmas holiday, President Barack Obama returned to Washington from Hawaii and the U.S. Senate reconvened Thursday as the deadline approached for going over the fiscal cliff of automatic tax hikes and spending cuts.

However, the House remained on Christmas break, with members warned they could be called back on 48 hours' notice if needed.

Hopes for a so-called grand bargain that would address the nation's chronic federal deficits and debt appeared dashed for now, with four days remaining to reach agreement on a smaller plan that would avoid the harshest effects of the fiscal cliff's tax increases and slashed spending.

With House Republicans unable to resolve the impasse, the focus shifted to the Democratic majority in the Senate to come up with a way forward that could pass the House and get signed into law by Obama.

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Negotiations on a deal to avoid the fiscal cliff got a jump-start on Monday with House Republicans offering a counter-proposal to President Barack Obama, but continuing to reject his call for higher tax rates on the wealthy.

The GOP proposal would result in $2.2 trillion in deficit savings over the next decade, including $800 billion from tax reform, $600 billion from Medicare reforms and other health savings, and $600 billion in other spending cuts, House GOP leadership aides told reporters.

House Speaker John Boehner called it a "credible plan that deserves serious consideration by the White House."

The move followed a weekend of accusations by both sides that the other was not serious about reaching a deal to avoid the automatic tax hikes and spending cuts scheduled to take effect January 1 - what is known as the fiscal cliff that economists say will damage U.S. growth.

There was no immediate response to the Republican plan, which congressional aides said would be sent in a letter to the White House.