This item has been updated.

A bipartisan budget agreement already passed overwhelmingly by the House now appears to have sufficient support to survive a key procedural test vote in the U.S. Senate later this week.

Final passage of the bill with a simple majority of senators doesn't appear in doubt -- but the legislation written by House Budget Committee Chairman Paul Ryan (R-Wis.) and Senate Budget Committee Chairman Patty Murray (D-Wash.) must first clear a procedural hurdle to end formal debate and proceed to final passage.

Supporters must garner at least 60 votes to proceed to final passage of the legislation. Assuming all 55 members of the Senate Democratic caucus vote "yes," they will need at least five Republicans to join them.

And on Monday, Sen. Orrin G. Hatch (R-Utah) appeared to deliver the critical fifth Republican vote. In a statement, he said that the budget agreement "isn’t everything I’d hoped it would be, and it isn’t what I would have written. But sometimes the answer has to be yes. The reality is that Republicans only control one-half of one-third of government. Ultimately, this agreement upholds the principles conservatives stand for and, with Democrats controlling the White House and the Senate, it is the best we could hope for."

Senators of both parties had hinted in recent days that the vote could be close, because Republicans who are usually inclined to join Democrats in pushing along key pieces of legislation, including Sens. John McCain (R-Ariz.), Susan Collins (R-Maine) and Lisa Murkowski (R-Alaska), remain upset with how Democrats have changed procedural rules regarding the confirmation of most presidential nominees. Several liberal Democrats also are unhappy that the budget agreement fails to extend unemployment insurance to millions of out-of-work Americans.

Much of the focus for this vote is on Republicans who usually vote with Democrats on cloture; some Republicans who might otherwise oppose the bipartisan budget deal, but have said in recent days that they are eager to avoid a government shutdown; and Democrats concerned that the legislation fails to extend unemployment insurance.

Here's a running tally of support for and against ending debate and final passage of the budget measure:

Support cloture and the budget agreement:

Sen. Saxby Chambliss (R-Ga.): He told reporters Monday evening that he's on board in both instances.

Sen. Susan Collins (R-Maine): She will vote to end debate and for the budget, a spokesman said Monday.

Sen. Orrin G. Hatch (R-Utah): "Ultimately, this agreement upholds the principles conservatives stand for and, with Democrats controlling the White House and the Senate, it is the best we could hope for," he said in a statement Monday.

Sen. Johnny Isakson (R-Ga.): He told the Atlanta Journal-Constitution Monday that he'll vote to approve the budget because "it finally gives America a budget to operate under and averts government shutdowns through 2015."

Sen. Ron Johnson (R-Wis.): "Although I disagree with a number of provisions in the bill, on balance the good outweighs the bad," Johnson said in a statement Sunday evening. "As long as the Senate does nothing to worsen the bill, I intend to support it."

Sen. John McCain (R-Ariz.): “I think it’s important that we have this agreement,” he told CBS’s “Face the Nation" on Sunday.

Supports cloture; undecided on the budget bill:

Sen. Jeff Flake (R-Ariz.): This is based on comments he made to reporters Friday.

Undecided on cloture; doesn't support the budget bill:

Sen. Charles E. Grassley (R-Iowa): A spokeswoman said Monday that he'll vote against the final budget agreement, but is unsure whether he'll vote for cloture.

Democrat who might have voted against the budget because it doesn't extend unemployment benefits:

Sen. Kirsten Gillibrand (D-N.Y.): The Empire State's junior senator will vote for the budget bill, despite being a vocal advocate for continuing the unemployment insurance.

Other key undecided senators:

Sen. Bernie Sanders (I-Vt.): One of the chamber's most liberal members remains undecided. A spokesman says he's concerned that the agreement doesn't extend unemployment insurance and that House Republicans quickly added the so-called "Doc Fix" before approving it last week.

Sen. Lisa Murkowski (R-Alaska): She usually votes with other Republicans to advance key legislation or nominees, but a spokesman says she's still undecided.

Sen. Sherrod Brown (D-Ohio): He hinted to reporters Friday that he has concerns about the lack of unemployment insurance.

Sen. Jack Reed (D-R.I.): With his state's high unemployment rate, he remains an advocate for extending unemployment insurance.

UPDATE: Sen. Richard Burr (R-N.C.): After initially suggesting through a spokesman that he'd vote to proceed to final debate, the senator said in a statement Monday afternoon that "I have decided upon further review to oppose allowing this bill to move forward. After reviewing in detail the significant changes made to the Senate budget rules that would allow Senate Democrats to circumvent the 60-vote threshold in order to pass a tax increase or increase spending, I have determined I cannot support cloture on the agreement."

Updated 6:41 p.m.