WASHINGTON, July 26 (Reuters) — The U.S. Senate could vote again this week on whether to begin debating a key piece of President Joe Biden's agenda, a $1.2 trillion bipartisan infrastructure plan to rebuild the nation's roads and bridges, if negotiators can finalize the details of the measure.

Senators from both parties worked over the weekend to try to finish the deal so that Senate Majority Leader Chuck Schumer could try again as early as Monday to open floor debate on the measure. Republicans blocked the Democrat's effort to start floor action last week, complaining they lacked the details of the deal.

Although negotiators and the Biden administration expressed optimism on Sunday, it was unclear how soon they could finalize the fine print of a complex measure in a tense political atmosphere.

The framework the senators and Biden announced a month ago, with $1.2 trillion in funding over five years, includes about $579 billion in new spending on roads, bridges, broadband and other public works projects.

"It's going to happen. ... This is what the American people want," Commerce Secretary Gina Raimondo said Sunday on CBS' "Face the Nation."

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Democrat Biden has said the plan is essential, but he also wants it to be followed by a much larger $3.5 trillion budget framework that would allow for spending on some of his other priorities, including climate measures and social spending. Republicans say they won't support the larger measure.

U.S. Senate Majority Leader Chuck Schumer, D-N.Y., walks to waiting car as he departs the U.S. Capitol in Washington on July 21, 2021. REUTERS/Elizabeth Frantz
U.S. Senate Majority Leader Chuck Schumer, D-N.Y., walks to waiting car as he departs the U.S. Capitol in Washington on July 21, 2021. REUTERS/Elizabeth Frantz

Sen. Rob Portman, the lead Republican negotiator on the bipartisan infrastructure plan, said Sunday on ABC's "This Week" that spending on mass transit was the only issue outstanding, and agreement could be reached this week.

"We're about 90% of the way there," he said.

Democrat Mark Warner, also a negotiator, told Fox News Sunday the text of the infrastructure proposal could be ready on Monday.

But a Democratic source close to the talks, speaking on condition of anonymity, said that in addition to mass transit, the two sides also remained apart on ensuring safe drinking water, expanding broadband internet access, repairing highways and bridges, and using unspent COVID-19 relief money to pay for the program. Another unresolved issue was a provision to lift workers' wages.

Other stresses continued to bedevil the process. Portman warned that House of Representatives Speaker Nancy Pelosi could sink the entire effort with her insistence, which she repeated on Sunday, that the Senate also pass the larger, $3.5 trillion spending measure before the House even takes up the bipartisan infrastructure bill.

"What she has just said is counter to what President Biden has committed to. ... It's the way we ought to be doing things here in Washington to get stuff done, and I can’t believe the speaker of the House would be blocking it," Portman told ABC.

(Reporting by Susan Cornwell; additional reporting by Richard Cowan; editing by Jonathan Oatis)