The defense, humanitarian and economic funding should pass comfortably, with the two parties having reached an agreement on the details, and it will likely move quickly through Congress.

"This is a large package but the need is great and time is of the essence... The president has called on both chambers of Congress to act quickly on the Ukrainian aid package, so act quickly we must," Chuck Schumer, who leads the Senate Democratic majority, said on the floor.

Congressional leaders struck a deal Monday to release $6.8 billion more than the $33 billion previously requested by the White House to help the Eastern European nation ward off Moscow's invasion.

The financial boost would include an extra $3.4 billion for both military and humanitarian assistance on top of the funding requested by the administration.

If the package passes as planned, US spending to bolster Ukraine's defenses against Russia's invasion and address the ensuing humanitarian crisis will soar to around $54 billion.

The action comes as a top US official warned that Russian President Vladimir Putin is preparing for a long war that may not end with Russian victory in the east.

"We assess President Putin is preparing for prolonged conflict in Ukraine during which he still intends to achieve goals beyond the Donbas," Director of National Intelligence Avril Haines said at a hearing on Capitol Hill.

She added that Putin was counting on US and EU resolve to weaken as the conflict continues to cause food shortages and inflation, including spiraling energy prices.

- Covid aid complications -

Debate and a vote on the legislation is expected in the House as early as Tuesday, likely followed by the Senate at the end of the week or next week.

The Democratic leadership had hoped to tie the Ukraine money to a new round of funding for Covid-19 tests, therapeutics and vaccines, with the United States experiencing a new spike in cases as it nears one million deaths.

But they decided against the move as they were unwilling to get drawn into another fight over border control, the issue that sank the previous attempt at a Covid funding deal before Easter.

House Democratic leaders are pushing for nearly $20 billion in additional pandemic preparedness funding, in line with what the White House said it needs.

The Senate had been considering a narrower package worth around $10 billion.

Republicans stopped the Covid aid package last month, demanding an amendment vote to keep in place Title 42, the pandemic-related provision used to deny asylum requests and allow the quick expulsion of migrants.

With the policy due to end on May 23, Democrats are reluctant to allow a vote, as several of their moderate lawmakers, and those in tough re-election fights, would likely vote with Republicans.

President Joe Biden said in a statement Monday that he was prepared to accept the decoupling of Ukraine and Covid aid, with "approximately 10 days" to go until the current funding runs out,

Biden signed into law the creation of a lend-lease program on Monday that will make it easier for the United States to send military equipment to Ukraine, more than 80 years after a similar program began America's involvement in World War II.