By Richard Cowan and David Morgan

WASHINGTON The U.S. Senate on Thursday was set to take up a bill to lift the government's $31.4 trillion debt ceiling, with just four days left to pass the measure and send it to Democratic President Joe Biden to sign, averting a catastrophic default.

The top Democrat and Republican in chamber vowed to do all they could to speed along the bill negotiated by Biden and Republican House of Representatives Speaker Kevin McCarthy, which would suspend the debt limit until Jan. 1, 2025 in exchange for a cap on spending.

It remained to be seen whether any members of their respective caucuses, particularly hardline Republicans angry the bill did not include deeper spending cuts, would use the Senate's arcane rules to try to slow down its passage.

The Treasury Department warned it will be unable to pay all its bills on June 5 if Congress fails to act.

The Republican-controlled House passed the bill on Wednesday evening in a 314-117 vote. McCarthy lost the support of dozens of his fellow Republicans.

"Once this bill reaches the Senate, I will move to bring it to the floor as soon as possible," Majority Leader Chuck Schumer said on Wednesday.

His counterpart, Senate Republican Leader Mitch McConnell, also signaled that he would work for fast passage, saying, "I'll be proud to support it without delay."

Biden's Democrats control the Senate by a thin 51-49 margin. The chamber's rules require 60 votes to advance most legislation, meaning at least nine Republican votes are needed to pass most bills, including the debt ceiling deal.

The measure faces opposition from the right, with some Republicans angry the spending cuts weren't deeper, and left, with some Democrats opposed to new work requirements imposed on some antipoverty programs. But most lawmakers acknowledged they could not stomach the prospect of barreling ahead into default.

Schumer and McConnell were working behind the scenes to dissuade opponents from erecting procedural barriers that would delay passage.

Typically on important, contentious bills such as this one, the two Senate leaders find a way to allow just a couple rebelling senators from each party to offer amendments under fast-track procedures, knowing they will lack the votes for passage.

"Unless you want to stay here through the weekend, I think some of our guys are going to need to get their votes" on their amendments, said Senator John Thune, the chamber's No. 2 Republican.

Any Senate changes to the bill at this stage would mean it would have to go back to the House for final passage, a delay that could make the first-ever U.S. government default a reality.

Republican Senator Rand Paul who regularly seeks such last-minute amendments, told CBS News on Wednesday he will not employ parliamentary procedures to delay action.

But another Republican, Mike Lee, has said he may try to slow it down. On Wednesday he vowed to vote against the bill, but did not reiterate his threat to try to delay it. Chastising House Republican negotiators for agreeing to what he sees as a weak compromise with Democrats, Lee lamented, "With Republicans like these, who needs Democrats?"

The bill was cobbled together over weeks of intensive negotiations between surrogates for Biden and House Speaker Kevin McCarthy. The main argument was over spending for the next couple years on "discretionary" programs, such as housing, education and medical research that Republicans wanted to cut deeply while seeking increases in funding for the military, veterans and possibly border security.

The nonpartisan Congressional Budget Office estimates would save $1.5 trillion over 10 years. That is below the $4.8 trillion in savings that Republicans aimed for in a bill they passed through the House in April, and also below the $3 trillion in deficit that Biden's proposed budget would have reduced the deficit over that time through new taxes.

The last time the United States came this close to default was in 2011. That standoff hammered financial markets, led to the first-ever downgrade of the government's credit rating and pushed up the nation's borrowing costs.

A default would trigger widespread financial consequences, triggering a recession that would hit everyone from poor people reliant on government aid to senior citizens expecting Social Security retirement checks and even wealthy Wall Street investors with fat portfolios in stocks and bonds.

(Reporting by Richard Cowan and David Morgan; Editing by Scott Malone and Lincoln Feast.)