WASHINGTON (Reuters) -The Democratic-led U.S. Senate is due to vote later on Wednesday to try to advance security assistance for Ukraine and Israel, despite Republicans’ determination to block the bill in a battle over immigration policy.

“The question before the Senate today is simple, yet momentous: will Senators agree to begin debate – just a debate – on legislation to defend America’s national security, on an issue so important it goes to the actual preservation of Western and democratic values in the world?” Democratic Majority Leader Chuck Schumer said in remarks opening the Senate.

But Republicans said they would vote on the procedural measure paving the way for the start of debate on the $110 billion security assistance bill.

“Today’s vote is what it takes for the Democratic leader to recognize that Senate Republicans mean what we say. Then let’s vote. And then let’s finally start meeting America’s national security priorities, including right here at home,” Senate Republican Leader Mitch McConnell said in a floor speech.

Congressional Republicans and Democrats have been debating for months how to address Democratic President Joe Biden’s request for billions of dollars in funding for Ukraine as it fights Russian invaders, Israel after the Oct. 7 attacks by Islamist Hamas militants, U.S. interests in the Indo-Pacific and international humanitarian relief.

But the White House’s two requests for Congress to pass spending bills have failed to advance, and tempers have become increasingly frayed on Capitol Hill as the impasse threatens to stretch into 2024. Democrats argue that aid for allies is essential to support global democracy and ward off autocracy.

“Make no mistake, today’s vote is going to be long remembered. History is going to be judged harshly … we can’t let (Russian President Vladimir) Putin win,” Biden said in remarks at the White House.

A group of Senate Democrats called a press conference to argue that the failure of the test vote would send a message to both U.S. adversaries and allies that the United States does not stand with its international partners.

“This is running out. We have but a few days for us to make clear, positive progress toward working out the final details necessary for us to show that the United States is a reliable ally,” Senator Chris Coons said.

Republicans contend that excessive illegal immigration across the southern border with Mexico is a hugely important security concern, and say they want more accountability than they are getting from the Biden administration for U.S. taxpayer funds that go abroad.

Schumer said on Tuesday he would try to break the impasse by offering Republicans the chance to add an amendment on border policy on legislation including aid to Ukraine and Israel to the $110.5 billion bill announced on Tuesday.

No such amendment had been announced by Wednesday afternoon.

(Reporting by Patricia Zengerle, additional reporting by Steve Holland and David Morgan; Editing by Alison Williams and Grant McCool)

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