Originally Published: 21 JUL 21 05:00 ET

Updated: 21 JUL 21 16:23 ET

By Alex Rogers and Manu Raju, CNN

(CNN) -- Senate Republicans blocked a vote Wednesday to start debate on a $1.2 trillion bipartisan infrastructure bill, as they push for more time to strike a deal with Democrats and write the legislation.

The vote was 49-51, short of the 60 votes needed to advance the measure.

But lawmakers said their negotiations will intensify over the next few days with the goal of trying again to advance the measure by early next week.

A group of 22 Democratic and Republican senators said after the vote that they are "close to a final agreement" and are "are optimistic that we will finalize, and be prepared to advance, this historic bipartisan proposal to strengthen America's infrastructure and create good-paying jobs in the coming days."

Senate Majority Leader Chuck Schumer defended his decision to set up the vote despite Republican opposition, pointing out that the bipartisan group has spent more than a month negotiating. He said Wednesday that bipartisan negotiators are "close to finalizing their product" and that GOP senators "should feel comfortable voting to move forward today."

"We all want the same thing here: to pass a bipartisan infrastructure bill," said Schumer. "But in order to finish the bill, we first need to start."

Senate Minority Leader Mitch McConnell said the push to advance the bill was a "stunt" that is "set to fail" because negotiators have not finalized an agreement.

"Around here, we typically write the bills before we vote on them," the Kentucky Republican said on the Senate floor. "That's the custom."

In June, the White House and a bipartisan Senate group agreed to a $579 billion in new spending to build roads, bridges, railroads and airports, along with water, power and broadband infrastructure projects.

But lawmakers have since struggled over how to pay for the massive investment. They made their task even harder by agreeing to scrap a provision that would have strengthened the Internal Revenue Service's ability to collect unpaid taxes, which would've raised up to $100 billion in government revenue. They also struggled to resolve other issues, including how much transit funding to provide, according to a Senate GOP source.

Utah Sen. Mitt Romney, one of the Republican negotiators, said Tuesday that senators had "resolved probably three-quarters" of their issues in the last two days, and predicted that they could work out the rest "by the end of the week."

Romney said that he wanted the vote to be pushed back to the beginning of next week.

"I am hoping that Sen. Schumer will have the vote on Monday when we've had a chance to resolve any remaining, outstanding issues," Romney said.

The bipartisan effort is one part of a two-track strategy to advance the White House's sweeping economic agenda, as Democrats lay the groundwork to advance a $3.5 trillion package expanding the social safety net. Democrats have suggested that some elements of the bipartisan plan could be rolled into the Democrat-only package if they can't advance the narrower measure.

But some moderate Democrats are already wary of the eye-popping price tag.

West Virginia Sen. Joe Manchin has balked at adding trillions more to the debt, and at some of the provisions addressing the production of fossil fuels.

Pressed on his concerns with the climate portions of the proposal, Manchin emphasized Wednesday that other nations are and will become the major contributors to climate change. He also said that he was worried that "we're hitting big, big debt."

Vermont Sen. Bernie Sanders predicted, however, that all 50 Democratic senators will ultimately support the budget resolution that would instruct committees to draft the $3.5 trillion legislation.

"At the end of the day, we will have all 50 on board for the most consequential piece of legislation for the families in the modern history," Sanders said.

This story and headline have been updated with additional developments Wednesday.