WASHINGTON (NewsNation Now) — It’s a consequential week for President Joe Biden’s agenda, as Democratic leaders delicately trim back his $3.5 trillion “Build Back Better” package to win over remaining lawmakers and work to quickly pass legislation to avoid a federal shutdown.

An expected Monday vote on a related $1 trillion bipartisan infrastructure package is now postponed until Thursday, amid ongoing negotiations. More immediately, the Senate has a test vote set Monday to keep the government funded and avert a federal debt default before Thursday’s fiscal year-end deadline. That package stands to run into a blockade by Republican senators — all but ensuring lawmakers will have to try again later in the week.

House of Representatives Speaker Nancy Pelosi expressed confidence Sunday that the $1 trillion infrastructure bill would pass this week.

“You cannot choose the date; you have to go when you have the votes in a reasonable time and we will,” she said. “I’m never bringing a bill to the floor that doesn’t have the votes,” she told ABC News “This Week” anchor George Stephanopoulos, walking back comments from Friday that she would bring it to the floor Monday.

“Let me just say that we’re going to pass the bill this week,” said Pelosi, a Democrat.

The measure was passed in the Senate with support from Democrats and Republicans on Aug. 10 and will help fund road, bridge, airport, school and other construction projects. It is also key to the success of President Joe Biden’s economic agenda.

Biden, asked at the White House on Sunday whether Pelosi had the votes she needed, expressed hopefulness: “I’m optimistic about this week. It’s going to take the better part of the week, I think,” he told reporters.

Pelosi also said it was “self-evident” Biden’s larger $3.5 billion social welfare and climate bill — whose massive cost has divided the Democratic Party — might shrink in size.

Democrats have so far failed to reach a consensus on the timing of the bills.

A large group of progressive lawmakers insist that the $1 trillion infrastructure bill be held back until the bigger bill is ready. Moderates want the $1 trillion bill enacted no matter the progress on the larger measure, which includes provisions for expanding healthcare for children and the elderly and for investing in steps to drastically reduce emissions blamed on climate change.

Republicans are lockstep opposed to Biden’s proposal, which would be paid for by increasing the corporate tax rate, from 21% to 26.5% on businesses earning more than $5 million a year, and raising the top rate on individuals from 37% to 39.6% for those earning more than $400,000 a year, or $450,000 for couples.

Two Democratic holdouts, Sens. Joe Manchin of West Virginia and Kyrsten Sinema of Arizona, also have said they won’t support a bill of that size. Manchin has previously proposed spending of $1 trillion to $1.5 trillion.

All this while Biden’s domestic agenda hangs in the balance, at risk of collapse and political fallout if he and Democratic leaders cannot pull their party together to deliver what could be a signature piece of legislation and the biggest overhaul of the nation’s tax and spending priorities in decades. Over the weekend, Biden personally spoke with lawmakers on the path forward, according to a White House official who requested anonymity to discuss the private conversations.

Pelosi did not specifically address how the divisions within the party would be overcome but said the final figure for the larger package would be lower than $3.5 trillion.

“That was the number that was sent to us by the Senate and by the president. Obviously, with negotiation, there has to be some changes in that the sooner the better, so that we can build our consensus to go forward,” she said.

The House Budget Committee advanced the larger bill Saturday, reporting the legislation with a favorable recommendation.

Pelosi was speaking ahead of a high-stakes week for both Democrats and Republicans in Washington. The U.S. Congress is fast approaching a Sept. 30 deadline to continue funding federal agencies or face the second partial government shutdown in three years.

In late October or early November, the U.S. Treasury will run out of money to pay its obligations, meaning the government faces the risk of a historic default if Congress does not act.

Republicans say they oppose the bill because it includes a temporary suspension of the debt limit, and while they oppose allowing the U.S. government to default, they want Democrats to suspend the debt limit without their votes.

Pelosi accused Republicans of being irresponsible and said the failure to extend the debt ceiling could have a broader impact on the U.S. economy.

“This is beyond a big deal,” she said.