WASHINGTON, Feb 4 (Reuters) - The U.S. Senate on Sunday unveiled a $118 billion bipartisan border security bill that would also provide aid to Ukraine and Israel following months of negotiations, but the measure faces an uncertain future amid opposition by Donald Trump and hardline Republicans.

Senate Majority Leader Chuck Schumer said he would take steps to hold an initial vote on the bill on Wednesday. If the bill were to become law, it would mark the most significant changes in U.S. immigration and border security in decades.

Independent U.S. Senator Kyrsten Sinema told reporters the legislation would secure the U.S. southern border, including by requiring the Department of Homeland Security to "shut down" the frontier to migrants if there are an average of more than 5,000 crossing attempts per day over seven days.

In addition to $20.23 billion for border security, the bill included $60.06 billion to support Ukraine in its war with Russia, $14.1 billion in security assistance for Israel, $2.44 billion to U.S. Central Command and the conflict in the Red Sea, and $4.83 billion to support U.S. partners in the Indo-Pacific facing aggression from China, according to figures from U.S. Senator Patty Murray.

An additional $10 billion would provide humanitarian assistance for civilians in Gaza, the West Bank and Ukraine.

The U.S. would provide $4.83 billion to support key regional partners in the Indo-Pacific where tensions have risen between Taiwan and China, as well as $2.33 billion for Ukrainians displaced by Russia's invasion and other refugees fleeing persecution.

"The priorities in this bill are too important to ignore and too vital to allow politics to get in the way," Schumer said in a statement. “The United States and our allies are facing multiple, complex and, in places, coordinated challenges from adversaries who seek to disrupt democracy and expand authoritarian influence around the globe."

The key overseas security provisions of the bill largely match what President Joe Biden requested from Congress in October, when he asked for additional funds for aid for Ukraine, Israel and Taiwan.

That request was stalled by House Republicans' insistence that it be tied to a shift in immigration policy.

"I urge Congress to come together and swiftly pass this bipartisan agreement," Biden said, also praising the migration measures in the bill.

Schumer said the agreement would provide more frontline personnel and asylum officers and provide "faster and fair" immigration decisions.

Mitch McConnell, the top Senate Republican, has supported the negotiations, saying Republicans would not get a better deal under a Republican White House.

"The Senate must carefully consider the opportunity in front of us and prepare to act,” McConnell said in a statement.

Schumer said in a news conference that he had never worked so closely with long-term Senate colleague McConnell as on the bill.

"At many occasions we thought the negotiations had fallen apart," Schumer said.

Other congressional Republicans have said Biden can enact many of the changes they want to immigration policy through executive action, though they had previously called for legislative action.

Immigration is the second largest concern for Americans, according to a Reuters/Ipsos poll published on Wednesday and is a top issue for Republicans specifically. The U.S. Border Patrol arrested about 2 million migrants at the border in fiscal year 2023.

Trump, the frontrunner for the Republican nomination to challenge Biden in the November election, has campaigned heavily on opposition to immigration. House Republicans are also pushing ahead with an effort toa impeach Biden's top border official, Homeland Security Secretary Alejandro Mayorkas.