With partisan squabbling increasing ahead of a vote to raise the nation's borrowing limit, aides to a bipartisan "gang of six" lawmakers in the Senate are working through a holiday recess on a deal to slash the country's skyrocketing debt and deficit.

Staffers for the group tell Fox News that their goal is to produce an agreement by May 2 to present to Congress when lawmakers return from their Easter break.

And with Monday's blunt warning from the credit rating agency Standard & Poor's about U.S. debt, and the financial markets' subsequent drop, the pressure is growing more intense.

"This is one more warning sign that the financial markets are paying close attention to see if we are serious about addressing our budget deficits and long-term debt," said Sen. Mark Warner, D-Va., a former governor and lead organizer of the so-called "gang of six," in a statement released by his office.

S&P, which downgraded its outlook on the U.S. from "stable" to "negative" for the first time since World War II, based its pessimism on doubts that Congress could overcome partisan gridlock to tackle the problem.

Fox News has learned that aides to the senators are working overtime to have a plan ready when lawmakers return to the Capitol, which will be less than two weeks from when the Obama administration estimates the government will have exhausted its $14.3 trillion debt limit.

The plan is expected to mirror one put forward by the president's own deficit commission, of which all six lawmakers were a part. The commission plan would cut the debt by roughly $4 trillion over 10 years, touching every area of the budget, including entitlements, taxes, and defense spending.

"They're working like mad. There's definitely a lot of pressure, but who knows if they'll get to a place that everyone can support. I think there's a growing feeling that they just have to," said one senior staffer close to the talks who requested anonymity, because of the sensitivity of the negotiations.

With Republicans promising to hold up Obama's request for a debt limit increase without major spending reductions and the White House warning of a "global economic calamity" if the ceiling isn't raised, the pressure on the negotiators is intense.

"The talks have almost collapsed a few times," according to another source familiar with the negotiations who also asked to remain anonymous in order not to jeopardize the deal. The source said the group is "in a much better place now."

"All the members are optimistic about getting a deal. It's been rough going at times, but they've stuck with it. It's too big a problem not to try to solve," said the staffer.

Gang members include Democratic Sens. Dick Durbin of Illinois, number two in his party's leadership, Warner, and Budget Committee Chairman Kent Conrad of North Dakota. On the Republican side are Sens. Tom Coburn, dubbed "Dr. No" for his fiscal hawk status, Saxby Chambliss of Georgia and Mike Crapo of Idaho.

While the other five are well-known figures in the Senate, Crapo has toiled outside the spotlight since he first came to Congress in 1998. In a chamber of headline-seekers, Crapo rarely attends news conferences and is not often seen in gaggles with reporters. But he is, perhaps, one of the most well-liked among his colleagues.

No one in the gang of six is up for re-election, a factor that no doubt aids in their potential success, though the similarities between the Republicans and Democrats pretty much stops there.

But given the severity of the U.S debt picture, the group appears to have checked partisan hats at the door, imbued with a sense of urgency. And it faces many obstacles, not the least of which is a looming presidential election year, during which little substantive legislation is likely to be achieved.

It certainly helps that the group, according to firsthand accounts, gets along well behind closed doors. Many meetings take place in Warner's fourth floor Russell Senate Office Building, mostly outside the path of reporters and cameras. The meetings typically switch off between members-only and staff. There usually is some kind of anteroom set up, according to a source, and the members and staff move back and forth conferring between the two.

One essential ingredient to the group's recipe for success? "They always have a big spread of food," said a source.

At one morning meeting, one budget expert baked homemade scones for the group. Sometimes, for the evening meetings, lawmakers meet over a glass of wine, according to the source. A little "gentle teasing" goes on between the members (Coburn and Durbin are especially known for this), but the members take the substance "quite seriously," said the source, adding, "There isn't really a single person pushing the talks along, it's a real group effort. You know, they frankly didn't know each other particularly well before this started, and they've grown pretty close over the last five months."

The good humor will serve the group well when and if they can produce a package. At least 20 senators, Republican and Democrat, are waiting for the finished product, anxious to support some kind of deficit and debt reform package ahead of any debt ceiling increase.

But there are many others who have cast a gloomy eye on the bipartisan work of the group. With Social Security reform on the table, according to Warner, the group is poised to run headlong into the powerful Senate Majority Leader, Harry Reid of Nevada, who told reporters recently, "Social Security has not contributed one penny to the deficit. Leave Social Security alone."

Then there's Mitch McConnell of Kentucky, Reid's GOP counterpart, and House Speaker John Boehner, R-Ohio, who have said, emphatically, that tax increases are off the table, a position long a part of GOP orthodoxy. But Chambliss, along with Coburn and Crapo, has said that times have changed and that, most definitely, tax hikes will be in the final product, likely in the form of eliminated tax deductions in favor of personal and corporate tax rate reductions.

"I'm taking arrows from some on the far right," Chambliss told the Rotary Club of Atlanta in a recent appearance with Warner, adding, "Are some people going to pay more in taxes? You bet."

That will, no doubt, mobilize the influential anti-tax advocacy group Americans for Tax Reform, run by Grover Norquist, who doggedly holds lawmakers to their no-tax-increase pledge.

Already, Coburn has been at loggerheads with Norquist merely for voicing support for a compromise on revenue measures, and the senator's spokesman now labels Norquist the "chief cleric of sharia tax law." And the arrows have continued in GOP circles, with one conservative blogger, Erick Erickson of Redstate.com, recently asking in a recent post, "Is Saxby Chambliss Becoming a Democrat?"

Still, even in the face of so much bipartisan opposition, gang members are increasingly signaling that a deal is near.

"I think there's a good chance that we'll be able to come up with a bipartisan agreement that people can swallow," Coburn predicted on "Fox News Sunday."

"Nobody is going to like what we come up with," Coburn added, "The left isn't going to like it, and the right isn't going to like it. And that's one thing that would be an indicator that is probably the best compromise we're going to be able to get. So, I think there's a good likelihood that we can get there. It's not a sure thing."

And Warner warned, "If we fail to take this seriously, and if our deficit and debt discussions turn into just another game of political brinksmanship, this could result in the most predictable economic crisis in our history."