By Makini Brice and Richard Cowan

WASHINGTON (Reuters) -The U.S. Congress on Wednesday has three days to avert a partial government shutdown, as leading lawmakers and their aides worked behind closed doors to overcome disagreements between the two parties and within the fractious House Republican majority over budget and policy priorities.

Senate Majority Leader Chuck Schumer, a Democrat, opened the Senate declaring that “we are very close” to an agreement on legislation funding a handful of government agencies through Sept. 30, the end of the current fiscal year.

Referring to the meeting he attended at the White House on Tuesday with President Joe Biden and the other three top bipartisan leaders of Congress, Schumer said: “We all agree a shutdown is a loser for the American people.”

But Schumer provided no details on the deal he said was imminent.

Meanwhile, House of Representatives Speaker Mike Johnson, a Republican, has offered Democrats the possibility of a fourth short-term stopgap measure to avert a government shutdown this weekend. But first, Democrats and Republicans would have to cut a deal on a number of fiscal 2024 appropriations bills that face staggered deadlines of March 1 and March 8 for the array of government agencies.

A continuing resolution, or “CR,” could extend the shutdown deadlines to March 8 and March 22.

“Any CR would be part of a larger agreement to finish a number of appropriations bills, ensuring adequate time for drafting text and for members to review prior to casting votes,” Johnson spokesperson Athina Lawson said in a statement.

Without passage of some sort of legislation by early Saturday, operations within the departments of Agriculture, Energy, Veterans Affairs, Transportation, and Housing and Urban Development could be curtailed. Construction at some U.S. military installations also could be stalled.

Schumer and Johnson have traded blame despite an agreement reached last month on $1.59 trillion in discretionary spending for the fiscal year.

Hardliners within Johnson’s thin Republican majority in the House have sought spending cuts and policy changes, including some related to abortion and food aid, on the funding bills, which Democrats have balked at.

A second deadline on a larger group of federal agencies, including the massive Defense Department and Department of Health and Human Services, which would run out of funding on March 8, also looms.

The furious closed-door negotiating comes as the current national debt stands at $34.3 trillion and is rapidly rising. Rating agency Moody’s said in September a government shutdown would hurt the country’s credit rating.

In addition to the government funding bills, Congress is also struggling to pass a $95 billion national security funding bill, including new aid for Ukraine and Israel, which Biden has urged. The Senate passed a bill, but it has been held up in the House.

“The situation in Ukraine is getting increasingly dire,” Schumer warned, as Kyiv runs out of ammunition and other weaponry in its battle against Russia, which invaded its neighbor two years ago.

“Speaker Johnson said he wants to continue to think it over,” Schumer said, referring to Tuesday’s White House meeting that included a spirited discussion of U.S. aid to Ukraine.

(Reporting by Makini Brice, Richard Cowan and David Morgan; Editing by Scott Malone, Lincoln Feast and Jonathan Oatis)