WASHINGTON (AFP) - The US Senate on Saturday gave itself four additional days to pass a US$1.1 trillion (S$1.4 trillion) federal spending Bill, easing the threat of a government shutdown that was looming at midnight.

Amid deep divisions between Republicans and Democrats over how to proceed on funding government through September, feuding lawmakers unanimously passed a measure that extends funds to late Wednesday.

The extension had already been approved by the House of Representatives, and it now goes to President Barack Obama for his signature.

It is the second extension passed by Congress in as many days as leaders struggle to finalize the spending Bill and bid farewell to the 113th Congress, one of the least productive sessions in modern history.

Senate Majority Leader Harry Reid and Minority Leader Mitch McConnell had expressed hope that a deal would be reached for a final vote Friday on the Bill funding nearly all federal operations through the end of fiscal 2015.

But that collapsed when conservatives, furious that the legislation failed to roll back Obama's recent unilateral immigration action to shield millions from deportation, refused to oblige.

The spending Bill faces a procedural test vote scheduled for about 1am (2pm Singapore time) Sunday - unless lawmakers agree to hold it earlier.

If no timing agreement is reached, a vote on final passage could come at 7am (8pm Singapore time) Monday at the earliest.

The Senate is also contending with up to 20 Obama nominations, including for the surgeon general position, that Democrats want to confirm before Republicans take full control of Congress in January.