“This represents moving away from political posturing, which has dominated since the election, to a proposal that will cause serious negotiations to start,” said Bruce Josten, vice president and chief lobbyist for the influential U.S. Chamber of Commerce, whose members have much at stake in any eventual deal.

A second stage of the Obama plan presented Thursday would involve overhauling the tax code and unspecific changes in Medicare and other entitlement programs totaling $400 billion.

The White House vigorously defended its proposal.

"Right now, the only thing preventing us from reaching a deal that averts the fiscal cliff and avoids a tax hike on 98 percent of Americans is the refusal of congressional Republicans to ask the very wealthiest individuals to pay higher tax rates,’’ said spokeswoman Amy Brundage.

Republicans were unimpressed. After meeting with Geithner Thursday and talking to Obama by phone Wednesday night, Boehner questioned if Obama and the Democrats are serious about cutting federal entitlement program spending.

“I’m disappointed in where we are, and disappointed in what’s happened over the last couple weeks,” Boehner said. “But going over the fiscal cliff is serious business. And I’m here seriously trying to resolve it. And I would hope the White House would get serious as well.”

Senate Minority Leader McConnell agreed.

“To date, the administration has remained focused on raising taxes and attending campaign-style events with no specific plans to protect Medicare and Social Security or reduce our national debt in a meaningful way,” McConnell said.

Democrats, though, insisted Republicans have come up with no serious plan of their own. After his meeting with Geithner, Senate Majority Leader Harry Reid, D-Nev., defended Obama and congressional Democrats.

“Really, now is the time for the Republicans to move past this happy talk about revenues, ill-defined, of course, and put specifics on the table. The president has made his proposal; we need a proposal from them,” Reid said.

William Douglas and Lesley Clark contributed.