Updated: 11:25 p.m.

Senate Majority Leader Harry Reid (D-Nev.) postponed a procedural vote on his budget plan Saturday night, just hours after Congressional Republicans announced they had re-entered negotiations with the White House and three days before a Treasury deadline to avoid government default.

The Senate is now slated to vote on the Reid plan, which lost significant momentum Saturday, on Sunday at 1 p.m.

“There are negotiations going on at the White House to avert a catastrophic default on the nation’s debt. There are many elements to be finalized and there is still a distance to go before any agreement can be completed, but I believe we should give everyone as much room as possible to do their work,” Reid said late Saturday night on the floor. He said that in several conversations with the White House throughout the evening, he was asked to give negotiators more time for a deal to be reached.

The new deal being discussed between the White House and Congressional leaders is strikingly similar to existing offerings from both Reid and Boehner, with approximately $1 trillion in immediate discretionary cuts and additional savings to be negotiated by a new Congressional committee tasked with producing a framework by year’s end.

The key sticking point yet again appears to be on a so-called “trigger,” or a built-in mechanism in the agreement that would pressure the newly created panel to actually produce the savings lawmakers seek.

“The trigger is the most important part of it right now. There’s a new approach to it, different approach, which I think will work. Key parts of its are unresolved. But it appears that both sides actively are trying to make it work,” Senate Majority Whip Dick Durbin (D-Ill.) said late Saturday.

“Sequestration is part of it obviously. They would have to have it. What we’re trying to do is how to make sequestration painful for both sides,” Durbin added, referring to mandatory across-the-board cuts, including to entitlements and defense spending, that would be enacted if the panel fails to produce the extra trillions in savings. Durbin denied earlier reports of a link between the expatriation of the Bush-era tax cuts and the second round of savings

Such a mechanism, however, is sure to raise ire from rank-and-file Democrats who would not want the added pressure of those types of cuts to be associated with the second phase of negotiations later this year. Democrats have for months insisted that any trigger or final deal include revenues in addition to spending cuts. But by bundling defense and Medicare cuts, Democrats could increase the pressure on Republicans in an election year to negotiate in good faith lest they appear to be favoring the wealthy at the expense of seniors or the troops.

Earlier Saturday, the original Reid plan, which would cut $2.4 trillion over the next 10 years in addition to establishing a panel to find more savings by the end of 2011, was voted down in the House.

Across the Capitol, 43 Senate Republicans sent a letter to Reid indicating they could not support the majority leader’s framework. Nevertheless, Congress is running out of time to dispatch legislation to President Barack Obama’s desk. Given Senate procedure, any single Senator could filibuster a vote on Reid’s plan, forcing the Nevada Democrat to use 30 hours at a time before moving on to the next phase of voting and requiring him to find 60 votes to proceed on the measure.

The news that McConnell and Speaker John Boehner were again in talks with the White House, after Boehner pulled back twice from such talks, seemed to catch Hill Democrats off guard. Democratic sources said that at the time, Republicans had not been engaging directly and that Kentucky Republican’s pronouncement set off Democratic leaders.

Reid and House Minority Leader Nancy Pelosi (D-Calif.) met with Obama at the White House Saturday, as McConnell and Boehner told reporters they were working with the administration and were “confident” a solution would be found to raise the debt ceiling and avert default.

Reid had secured the White House’s blessing earlier for his plan, but Saturday’s developments seemed to indicate he was at risk of being edged out of talks yet again. Late Saturday night, Senate Democratic aides pointed to Reid’s closing remarks as indication of his willingness to find an agreement, saying that he is actively participating in discussions and that any agreement reached will include a long-term extension of the debt ceiling, a requirement that has united Democrats even when they have diverged from the White House position on trickier issues like entitlements.

Reid and McConnell engaged in a series of uncomfortable exchanges on the Senate floor Saturday, with the most tense sparring match coming after he had returned from the White House. Reid had requested the presence of all Senators to the floor, only to say that McConnell’s characterization of a deal being “close” between the GOP and the White House were “untrue.”

McConnell fired back: “I might say, I actually cut short a conversation with the vice president to come out here for this live quorum. I’d like to get back to work so we can hopefully solve this problem.”

Even Republican rank and file leaving the floor seemed to be projecting conflicting messages. Sen. Saxby Chambliss (R-Ga.) told a small group of reporters, when asked whether an agreement was closer, that talks had gone “the other way.” Moments later, Sen. Tom Coburn (R-Okla.) said that he had just talked to McConnell and got “good vibes” about an imminent deal.

The swiftly changing tides, both political and legislative, come against the backdrop of a ticking clock that is adding pressure to all sides to broker a deal. But it’s possible Obama alienated Democrats Saturday by again working around them to try to find a solution with Republicans, especially if he put entitlements back on the table without also including revenues, which long has been the Democratic demand.

Alan K. Ota contributed to this report.