(CNN) - A mere two weeks before the congressional budget super committee's November 23 deadline, GOP members of the deficit-reduction panel have signaled a willingness to accept tax increases as part of a broader deficit reduction package, CNN learned Tuesday.
The development has the potential to break a deadlock within the sharply polarized 12-member group, as top Republicans have long been adamantly opposed to any tax hikes. A Senate GOP leadership aide called the shift a "significant concession" on the part of Republicans.
Democrats immediately rejected the offer, characterizing it as political gamesmanship.
The Republican proposal is based primarily on new limits on itemized tax deductions and credits for individuals, according to a Republican aide close to the discussions. The deduction for mortgage interest on second homes - a provision of the tax code used primarily by wealthier Americans - is one possible example, the aide said.
Sen. Patrick Toomey, R-Pennsylvania, helped to push the proposal during talks with Senate Finance Committee Chairman Max Baucus, D-Montana, aides said.
In exchange for the new revenue generated by closing the loophole, Republicans want Democrats to agree to lower the top marginal income tax rate for individuals from 35% to 28% according to two Democratic sources. Republicans are also looking for significant changes to entitlement programs, including Medicare, Medicaid and Social Security.
One GOP aide asserted the Republican offer would generate hundreds of billions of dollars in new revenue, but refused to offer a specific figure.
"We are committed to doing what is needed to help avoid" automatic cuts, the aide said. "Their demand is tax increases have to be on the table, (and) that's something we're willing to look at."
Democrats quickly dismissed the offer, with aides calling it "not serious" and "a joke." Democrats accused their Republican counterparts of trying to shift blame for the stalled negotiations and disputed Republican claims their proposal would generate billions of dollars in new revenue.
"This plan would provide the very wealthiest American with one of the largest tax rate cuts ever. It's a shell game," one Democratic aide close to the committee told CNN. It is "a thinly veiled attempt to appear to put revenue on the table while simultaneously removing far more with massive tax cuts for wealthy Americans. This plan is not a solution Democrats or middle class Americans would ever be willing to accept."
"I've yet to see a real credible plan that raises revenue in a significant way to bring us to a fair and balanced proposal," said super committee co-chair Sen. Patty Murray, D-Washington.
Senate Minority Leader Mitch McConnell, R-Kentucky, avoided directly addressing the question of new revenue.
"I can tell you with certainty that the six Republicans on the (super committee) want an outcome, do not believe failure is an option and we're working toward that end as diligently as we can," McConnell insisted.
The Republican leader said he suspects "folks down at the White House are pulling for failure."
"If the (super committee) succeeds, it steps on the story line that they have been peddling, which is that you can't do anything with the Republicans in Congress," he said.
The 12-member super committee is tasked with finding at least $1.2 trillion deficit savings over the next 10 years. Assuming a majority on the panel can reach an agreement by November 23, Congress will vote on its recommendations by December 23.
–CNN's Deirdre Walsh, Alan Silverleib and Ted Barrett contributed to this story.