To reduce government red ink, Republicans are willing to raise government revenues, but not increase taxes. Congressional Democrats would accept reductions in Medicare spending, yet no cuts in benefits.
Parsing these distinctions appears to be key to the deficit reduction talks headed by Vice President Joe Biden, particularly with Republicans eager to protect their anti-tax credentials in 2012 and Democrats ready to campaign aggressively against a House GOP plan to remake Medicare.
In recent days, Senate Republicans have voted to end the government's subsidy of ethanol, raising questions about other tax breaks that might be eliminated as a way to reduce deficits.
On the other side of the aisle, Democrats are prodding President Barack Obama to rule out Medicare benefit cuts as part of any agreement. In private meetings, he has yet to do so, according to numerous officials.
The negotiators met on Tuesday as they accelerated efforts to line up a deficit-cutting deal that would accompany legislation raising the nation's $14.3 trillion debt limit.
"We are meeting every day for the remainder of this week," Treasury Secretary Tim Geithner told business executives before heading to the Capitol.
Geithner has warned that the government could be forced into its first-ever default on obligations if there is no increase in the debt limit by Aug. 2, with catastrophic consequences for a struggling economy.
Increasingly in recent days, officials in both parties say that rather than a formal agreement, the Biden-led talks are likely to result in a consensus list of options for cutting deficits. The negotiations would then largely, if not entirely, be turned over to President Barack Obama, House Speaker John Boehner, Senate Majority Leader Harry Reid, House Democratic leader Nancy Pelosi and Senate Republican leader Mitch McConnell, perhaps as soon as the end of the week.
The administration has told lawmakers that a $2.4 trillion increase in borrowing authority is needed to get through the 2012 elections, and Boehner has said deficit cuts must be higher than any debt limit increase.
In the interim, House Republicans also have discussed the possibility of drafting and passing their own package of cuts, coupling it with a debt limit increase of unknown size and sending it to the Democratic-controlled Senate.
As described by officials, any such move would mirror the strategy Boehner and the GOP leadership employed earlier this year while negotiations with the White House remained unresolved over a catch-all spending bill. At the time, the House approved a pair of bills to keep the government in operation for a brief period while cutting spending by a few billion dollars.
In that case, Republicans wanted to demonstrate that they opposed a government shutdown despite persistent Democratic claims to the contrary.
Separately, McConnell said that without changes to benefit programs, "we'll probably end up with a very short-term proposal over, you know, a few months. And we'll be back having the same discussion again in the fall."
Several officials have said the chances for a sweeping agreement likely will hinge on a trade-off in which Democrats accept cuts in benefit programs, including Medicare, while Republicans acquiesce in increased revenues.
The administration wants roughly equal amounts of deficit reductions from each category, according to numerous Democratic officials.
Republicans are pushing back.
"Some Democrats are insisting that they'll only agree to cuts if Republicans agree to raise revenue," McConnell, R-Ky., said in remarks on the Senate floor shortly before the day's negotiating session began. "That's Washington speak for tax hikes, and it's absurd."
But 33 of the Senate's 47 Republicans joined in a vote last week to eliminate the federal subsidy for ethanol, suggesting some flexibility on the issue.
Sen. Lindsey Graham, R-S.C., said over the weekend that additional changes might be possible along the same lines.
"No one on the Republican side's going to vote to raise taxes, but I think many of us would look at flattening the tax code, do away with deductions and exemptions, and take that revenue to help pay off the debt," he said.
But Sen. Orrin Hatch of Utah, said his vote to end the subsidy was an exception that "should not be viewed as a precedent for increasing taxes."
"Tax reform should be kept separate from the debt reduction negotiations," he said. "If not, then fixing our broken tax system won't be the goal _ raising taxes will be."
If the Republican position on taxes is somewhat ambiguous, so, too, is the Democratic stance when it comes to Medicare.
The party's leaders in Congress say they oppose any cuts in Medicare benefits, and express concern that Obama might accept them in a final trade-off with Republicans.
At a private meeting at the White House this month, Pelosi and Rep. Henry Waxman of California were among several lawmakers who pressed the president on the subject without success, according to participants in the session.
Publicly, Democrats use the issue to attack Republicans, although some of their comments seem directed at Obama, as well.
"We want to make our position on Medicare perfectly clear: No matter what we do in these debt limit talks, we must preserve the program in its current form, and we will not allow cuts to seniors' benefits," Sen. Chuck Schumer, D-N.Y. said at a news conference last week.
In a speech earlier this spring, Obama called for additional Medicare savings, but he provided only sketchy details.
An accompanying White House document said the cuts should come from "excessive spending on prescription drugs" and slowing the increase in the per-patient cost.
Associated Press writers Ricardo Alonso-Zaldivar, Martin Crutsinger, Jim Kuhnhenn and Andrew Taylor contributed to this report.