WASHINGTON/PALM BEACH, Fla. (Reuters) - Democrats in the U.S. Congress on Monday will try to push through expanded $2,000 pandemic relief payments for Americans after President Donald Trump backed down from a fight with lawmakers that could have shut down the federal government.

In a sudden reversal late on Sunday, Trump signed into law a $2.3 trillion pandemic aid and spending package, restoring unemployment benefits to millions of Americans and providing funds to keep government agencies running.

Trump, who leaves office on Jan. 20 after losing November's election to Democratic challenger Joe Biden, retreated from his threat to block the bill, which was approved by Congress last week, after he came under pressure from lawmakers on both sides.

The Republican president, who played golf in Florida on Sunday and remained out of public view even as a government crisis loomed, had last week called the bill a "disgrace" and demanded Congress change it to boost stimulus payments for struggling Americans from $600 to $2,000 while also cutting other spending.

It was unclear why Trump, who has refused to concede defeat to Biden, changed his mind on the stimulus package. His surprise, last-minute resistance had threatened to inject further chaos into the final stretch of his presidency.

Despite that, Democratic lawmakers who have a majority in the House of Representatives and have long wanted $2,000 relief checks, hope to use a rare point of agreement with Trump to advance the proposal - or at least put Republicans on record against it - in a vote on Monday.

Voting is not expected until late in the afternoon, when lawmakers will also seek to override Trump's recent veto of a $740 billion bill setting policy for the Defense Department. If successful, that would be the first veto override of Trump's presidency.

Many of Trump's fellow Republicans, who control the Senate, oppose the higher relief payments, and Trump may not have the influence to budge them.

Georgia Republicans Kelly Loeffler and David Perdue, who face crucial Senate runoffs next month that could determine who controls the chamber, welcomed Trump's move, without saying whether the payments should be increased.

"Thanks to President Trump's leadership, COVID relief is again on its way to millions of Georgia families and businesses who need it most," they said in a joint statement that echoed Trump in criticizing the Democrats for prioritizing "wasteful, irresponsible spending over the welfare of the American people."

Many economists agree the financial aid in the bill should be bigger to jolt the economy but say that any immediate support for Americans hit by coronavirus lockdowns is still urgently needed.

Global markets were buoyed after Trump signed the massive spending measure and backed away from a year-end government spending crisis. U.S. stocks also rose in pre-market trading, with futures tracking the S&P 500 and Nasdaq hitting a record high.

After signing the bill behind closed doors at his beachside club in Florida, Trump sought to put the best face on his climb-down, saying he was signing it with "a strong message that makes clear to Congress that wasteful items need to be removed."

"Much more money is coming," he said in a statement, though he provided nothing to back this promise.

BITTER HOLIDAY

Unemployment benefits being paid out to about 14 million people through pandemic programs lapsed on Saturday but will be restarted now that Trump has signed the bill.

The delay, however, forced people to lose a week of some federal jobless aid that had been extended under the measure, Washington Governor Jay Inslee said, even as he and other governors in both parties welcomed the bill's signing.

"It is good news that the president has signed the relief bill. But his delayed action cost Washingtonians a week of PUA (Pandemic Unemployment Assistance) benefits," Inslee, a Democrat, tweeted.

The relief package extends a moratorium on evictions that was due to expire on Dec. 31, refreshes support for small-business payrolls, provides funding to help schools re-open and aid for the transport industry and vaccine distribution.

It includes $1.4 trillion in spending to fund government agencies and avert a government shutdown that would have begun on Tuesday had Trump not signed the legislation.

Americans are living through a bitter holiday season with a pandemic that has killed nearly 330,000 people in the United States and a daily death toll now repeatedly well over 3,000, the highest since the pandemic began.

(Reporting by Susan Cornwell in Washington and Steve Holland in Palm Beach; additional reporting by Susan Heavey. Writing by Matt Spetalnick and David Brunnstrom. Editing by Kieran Murray, Chizu Nomiyama and Steve Orlofsky)