WASHINGTON, Nov 13 (Reuters) - President-elect Donald Trump and President Joe Biden, longtime political rivals, met on Wednesday for the first time since Trump won back the White House last week and both promised a smooth transfer of power in January.

The two leaders sat side by side before a roaring fire in the Oval Office, a peaceful scene that belied tensions between them.

Biden, a Democrat, defeated Trump in the 2020 election but dropped out of the 2024 race in July after a disastrous debate with the Republican Trump. He handed his candidacy to Vice President Kamala Harris, who lost.

"We're looking forward to having, like we said, a smooth transition, do everything we can to make sure you're accommodated, what you need," Biden said. "Welcome, welcome back."

"Politics is tough, and it's many cases not a very nice world, but it is a nice world today, and I appreciate very much a transition that's so smooth it'll be as smooth as it can get, and I very much appreciate that, Joe," said Trump, who takes over on Jan. 20.

Reporters shouted questions but were quickly ushered out.

It was a sharp contrast to the criticism the two men have hurled at each other for years. Their respective teams hold vastly different positions on policies from climate change to Russia to trade.

Trump's motorcade rolled through the heavily guarded White House gate. Biden greeted the former and future president in the Oval Office.

First lady Jill Biden joined Biden in greeting Trump on his arrival. The White House said she gave Trump a handwritten letter of congratulations for his wife, Melania Trump, and "expressed her team’s readiness to assist with the transition."

Biden, 81, has portrayed Trump as a threat to democracy, while Trump, 78, has portrayed Biden as incompetent. Trump made false claims of widespread fraud after losing the 2020 election to Biden.

TRUMP MEETS REPUBLICAN LAWMAKERS

Trump celebrated his victory earlier in the day with Republicans in the House of Representatives who have a good chance of maintaining control of the chamber as Nov. 5 election results trickle in.

"Isn't it nice to win? It's nice to win. It's always nice to win," Trump said. "The House did very well."

Biden, who initially ran against Trump in the 2024 election before stepping aside and endorsing Vice President Kamala Harris as the Democratic nominee, will welcome the former and future president into the Oval Office, a traditional courtesy by outgoing presidents that Trump, a Republican, did not extend when Biden won in 2020.

"He believes in the norms, he believes in our institution, he believes in the peaceful transfer of power," White House spokesperson Karine Jean-Pierre said of Biden's decision to invite Trump. She spoke at a briefing for reporters on Tuesday.

Outside the White House gates, signs of the impending power transfer were evident with construction already under way for the stands for VIP guests to sit during the parade that will take place after Trump is inaugurated.

TRANSITION PARTIALLY STALLED

Although Biden intended to use the meeting to show continuity, the transition itself is partially stalled.

Trump’s team, which has already announced some members of the incoming president's cabinet, has yet to sign agreements that would lead to office space and government equipment as well as access to government officials, facilities and information, according to the White House.

“The Trump-Vance transition lawyers continue to constructively engage with the Biden-Harris Administration lawyers regarding all agreements contemplated by the Presidential Transition Act," said Brian Vance, a spokesperson for the Trump transition, referring to the law that governs the transfer of power.

Valerie Smith Boyd, director of the Partnership for Public Service’s Center for Presidential Transition, a non-profit that advises incoming administrations, said the agreement underscores that the United States only has one president at a time and includes pledges to sign ethics pacts not to profit off information provided in the transition.

“That needs to be signed for interaction to begin with federal agencies,” she said. “Everything is hinging on that.”

Meetings with federal agencies aside, Biden and Trump will likely discuss a myriad of topics, including foreign policy.

The outgoing president may urge Trump to back Ukraine in its war with Russia. U.S. support for Kyiv is in question following Trump's victory over Harris last week, and Trump has pledged to end the war quickly without explaining how.

Jean-Pierre declined to outline discussion points between the two men ahead of their meeting.

The meeting will be the first since the two men's debate in June. Biden's poor performance then heightened concerns about his age among fellow Democrats and led to his departure from the race. Harris became the Democratic nominee instead, running a truncated campaign that ended in her loss.

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Reporting by Jeff Mason; additional reporting by Heather Timmons, Richard Cowan, Steve Holland, Tim Reid and Rami Ayyub; Editing by Leslie Adler and Howard Goller