For weeks, it had looked as if the year-long effort to reach a debt deal by the so-called Gang of Six in the Senate was defunct, a victim of the polarization in Washington, especially when it comes to taxes.

But looks can be deceiving.

“We were never as dead as the press thought we were,” Senator Mark R. Warner, a freshman Democrat from Virginia, said in an interview.

Mr. Warner, a centrist former governor, has made reaching a deal to reduce the nation’s deficit the primary goal of his early tenure in the Senate. He started nearly as soon as soon as he arrived in Washington, leading the “gang” with Senator Saxby Chamblis, Republican of Georgia.

“There have been some long nights where I wanted to pull out my hair,” he said Tuesday evening, adding that in recent weeks, finding a way to a deal had become an “obsession.”

That obsession appears to have paid off.

With the deadline for raising the nation’s debt ceiling just 14 days away, Mr. Warner and the other five senators — three Republicans and three Democrats in all — appear to have given new life to a grand bargain with President Obama that could reduce the nation’s deficit by about $4 trillion over the next decade.

In an early afternoon news briefing, Mr. Obama called the proposals unveiled by the senators on Tuesday morning “good news” and a “very significant step.”

Senators from both parties appeared optimistic as well. Forty-nine of them, from both parties, attended a briefing by Mr. Warner and his group’s members on Tuesday morning. Mr. Warner said the reaction had been positive.

“You could almost feel a sigh of relief as people said, ‘Oh my gosh, here’s something that we could be for,’” Mr. Warner said.

But Mr. Warner, a veteran of high-stakes negotiations with Republicans from his time in Virginia’s executive mansion, remains wary and nervous that the entire thing could fall apart at any moment during the next two weeks.

There are, he predicted, many ways it could unravel.

Republicans in the House, who have stated their opposition to any tax increases, could continue to balk at the proposals, which raise nearly $1 trillion in new revenue by lowering rates while closing tax loopholes.

Republican members of the “gang” are trying to persuade House members to support the plan, he said. “There are a number of our Republican colleagues who are working hard on this,” Mr. Warner said.

Democrats, too, will need to be brought along to support the idea that entitlement programs like Medicare and Social Security can be modified without sacrificing their basic nature. A deal could be scuttled if Democratic opposition to some of those proposals develops.

Time is also a problem.

The nine-page document that Mr. Warner and his Senate partners released on Tuesday is far from finished legislation, and there is just not time to finalize it before the debt ceiling deadline of Aug. 2. Lawmakers could conclude it’s a road too far, he conceded.

“I’ve been up and down on this,” he said. “There are still so many hurdles.”

Mr. Warner is no stranger to such obstacles. In 2004, he led a year-long effort to pass a tax reform plan in Virginia that addressed what he called at the time the state’s “structural deficit.” His plan involved a series of tax changes that he said would mean that 95 percent of Virginians would pay less, over all, in taxes.

But it also proposed raising $1.2 billion in new revenue for the state, drawing intense opposition from the Republican-controlled majorities in the state House and Senate.

To overcome those odds, Mr. Warner targeted 17 moderate Republican House delegates, wooing and pressuring them for months until they all broke away from their leadership to support the tax plan. For their efforts, those Republicans earned a place on a “Least Wanted” poster distributed by Grover Norquist’s Americans’ for Tax Reform. The poster predicted that “a posse of taxpayers may send them away.”

Mr. Warner on Tuesday recalled his success — however difficult — in Virginia, and predicted a similar result in Washington.

“Just remember 2004,” he said in the interview. Later, Mr. Warner told Virginia reporters that the fight in Washington was “2004 on steroids.”

Last month, it looked like Mr. Warner’s efforts in Washington would amount to little when Senator Tom Coburn, Republican of Oklahoma, dropped out of the group, saying he could not support the idea of tax increases being discussed.

The effort appeared over. The focus of attention shifted quickly, first to talks being hosted by Vice President Joseph R. Biden Jr. and then to brief discussions between Mr. Obama and House Speaker John A. Boehner at the White House.

Even as the clock ticked away, and testy negotiations at the White House continued day after day, Mr. Warner’s effort seemed to sink further into irrelevance.

But Mr. Coburn announced Tuesday morning that he had rejoined the Gang of Six, and Mr. Warner said he was circulating a letter he hoped would be signed by the 49 other senators who attended the briefing.

“This is, I hope, a major step forward toward a bipartisan, comprehensive and bold approach to take on this question about our nation’s debt and deficit,” he told the Virginia reporters.

But for Mr. Warner, a former tech executive who made millions co-founding Nextel, optimism is fleeting.

“Nothing’s a deal until everything’s a deal,” he said in the interview.

Asked whether he thought a deal would be reached, he paused and added, “I’ve been so down, I don’t want to get too up today.”