By Patricia Zengerle

WASHINGTON The Democratic and Republican leaders of the U.S. Senate expressed support for continued assistance for Ukraine on Tuesday, as lawmakers returned to Washington facing a tight deadline for passing spending bills.

President Joe Biden last month asked Congress to approve about $40 billion in additional spending, including $24 billion for Ukraine and other international needs, in a test of the country's willingness to keep supporting Ukraine as it fights Russian invaders.

"We also must continue standing with our friends in Ukraine, now more than ever, as the counteroffensive against Putin's forces is in full swing," the Senate's Democratic majority leader, Chuck Schumer, said in remarks opening the Senate after its August recess.

"The Senate's top priority must be keeping the American people safe. And this month we'll have the chance to do that with supplemental appropriations for urgent national security and disaster relief priorities," Republican leader Mitch McConnell said.

"We need to continue to invest in America's defense industrial base, both to support our partners in today's fight and to help our forces deter tomorrow's threats," he said.

Biden's national security adviser, Jake Sullivan, told reporters at the White House earlier on Tuesday that the administration was working closely with both the Senate and House of Representatives on the supplemental aid package, which seeks funding through the end of 2023.

Sullivan said the administration believed it would be able to secure the necessary funding. "The conversations have been constructive, they've been positive they've been substantive and we anticipate being able to work our way through to a sound package so that Ukraine can get what it needs," he said.

Prospects for Biden's supplemental request could be less bright in the House, where Republicans hold a slim majority and some on the far right, particularly those most closely allied with former Republican President Donald Trump, have been critical of U.S. funding for Kyiv.

Biden's request for Ukraine aid comes as lawmakers face an Oct. 1 deadline to pass at least a short-term spending bill or face an embarrassing government shutdown.

(Reporting by Patricia Zengerle, additional reporting by Katharine Jackson; editing by Grant McCool)