By Andrea Shalal

WASHINGTON The White House on Wednesday appealed to Congress to approve billions of additional dollars of support for Ukraine as its counteroffensive against Russian forces continues while the weather cools and conditions grow more difficult.

U.S. President Joe Biden is looking forward to getting a "battlefield perspective" from Ukrainian President Volodymyr Zelenskiy when they meet at the White House on Thursday, White House spokesperson John Kirby told reporters.

"It (is) really a critical time as we head into the fall," Kirby said, adding the White House had encouraged Zelenskiy to meet with U.S. lawmakers to make his case for continued military support, given opposition voiced by some members.

"It's vital that we get that supplemental passed," he said, adding the cost would be "exorbitantly higher" if Russian President Vladimir Putin was allowed to take control of Ukraine and pushed through to the border of NATO.

"If you think that the cost of supporting Ukraine is high now, just ponder how exorbitantly higher it would be in blood and treasure if we just walk away and let him take Ukraine," he said. "Then the cost of defending sovereign integrity and territory, believe me, gets a whole lot more expensive in both blood and treasure, including American blood."

Biden, a Democrat, has been pressing Congress to provide an additional $24 billion for Ukraine and other international needs amid Russia's ongoing invasion. Biden's fellow Democrats control the U.S. Senate, but Republicans narrowly control the U.S. House of Representatives and have signaled resistance to the request.

"We think it's really important for members of Congress to be able to hear directly from President Zelenskiy about what he's facing in this counteroffensive and ... what he needs to continue," Kirby said. "He's the best messenger for the people of Ukraine and his armed forces."

Zelenskiy is due to meet with Biden on Thursday afternoon after addressing Congress and meeting with U.S. military officials.

It will be their sixth in-person meeting, and Zelenskiy's third visit to the White House, Kirby said.

U.S. officials have said Biden plans to announce additional aid to Ukraine, but Kirby gave no details.

He said there were "active" discussion about providing Army Tactical Missile Systems (ATACMS) that can fly up to 190 miles (300 km) to Ukraine, but no decision had been made.

Kyiv has repeatedly asked the Biden administration for ATACMS to help attack and disrupt supply lines, air bases and rail networks in Russian occupied territory.

Kirby said Ukraine was making progress in its counteroffensive, but it was "clearly" not over, and "they are going to continue to need all the support that they can get to keep that advance going."

(Reporting by Andrea Shalal and Eric Beech; Editing by David Gregorio)