WASHINGTON (Reuters) - Joe Biden arrived at the U.S. Capitol on Wednesday morning for his presidential inauguration, ready to take over a country battered by the coronavirus pandemic and to put an end to a tumultuous four years under President Donald Trump.

Democrat Biden, 78, will become the oldest U.S. president in history at a scaled-back ceremony in Washington that has been largely stripped of its usual pomp and circumstance, due both to the coronavirus and security concerns following the Jan. 6 assault on the U.S. Capitol by Trump supporters.

Trump, a Republican, left the White House with his wife Melania just after 8 a.m. (1300 GMT) and went by helicopter to a sendoff event at Joint Air Force Base Andrews, where he promised supporters "we'll be back in some form" and extolled his administration's successes before flying off to Florida.

Top Republicans, including Vice President Mike Pence, were not there to see him go. Biden arrived at the Capitol just before 10:30 (1530 GMT) for his inauguration after a visit to church, where he was joined in a show of unity by the two most senior Republicans in Congress: Senator Mitch McConnell and House of Representatives Minority Leader Kevin McCarthy.

With only a small number of attendees present, Biden will take the oath of office before U.S. Chief Justice John Roberts just after noon (1700 GMT), placing his hand on an heirloom Bible that has been in the Biden family for more than a century.

Trump flouted one last convention on his way out. His refusal to attend his successor's swearing-in breaks with more than a century and a half of political tradition, seen as a way of affirming the peaceful transfer of power.

The president did, however, leave a customary note for Biden in the Oval Office, according to a White House official, though it was not yet known what it said.

Biden's running mate, Kamala Harris, the daughter of immigrants from Jamaica and India, will become the first Black person, first woman and first Asian American to serve as vice president after she is sworn in by U.S. Supreme Court Justice Sonia Sotomayor, the court's first Latina member.

The ceremony will unfold in front of a heavily fortified U.S. Capitol, where a mob of Trump supporters stormed the building two weeks ago, fired up by his false claims that the Nov. 3 election was stolen with millions of fraudulent votes.

The violence, which left five dead, prompted the Democratic-controlled U.S. House to impeach Trump last week for an unprecedented second time.

Thousands of National Guard troops were stationed on Wednesday around the Capitol, where barbed wire topped high fences and both guests and members of the press passed through multiple checkpoints. Access was strictly limited and required a government-conducted COVID-19 test within 48 hours of arrival.

Former Presidents Barack Obama, George W. Bush and Bill Clinton, as well as their spouses, also arrived at the Capitol. Pence and other top Republicans were on hand as well.

Instead of a throng of supporters, the National Mall was covered by nearly 200,000 flags and 56 pillars of light meant to represent people from U.S. states and territories.

"It is grim and beautiful at the same time," U.S. Representative Jared Huffman, a California Democrat, said of the flags filling the Mall.

'SOUL OF AMERICA'

Biden, who has vowed to "restore the soul of America," will call in his inaugural address for American unity at a time of crisis, according to advisers.

He will also waste little time trying to turn the page on the Trump era, advisers said, signing a raft of 15 executive actions on his first day in office on issues ranging from the pandemic to the economy to climate change.

The orders will include mandating masks on federal property, rejoining the Paris climate accord and ending Trump's travel ban on some Muslim-majority countries.

Trump, who grew increasingly isolated in the waning days of his tenure, has still not explicitly conceded the election.

In his final remarks as president on Wednesday, Trump listed his successes, including the "medical miracle" that yielded a coronavirus vaccine in less than a year, and said serving as president was his "greatest honor." He did not mention Biden by name.

"Have a good life - we will see you soon," Trump said before boarding Air Force One to head to his Mar-a-Lago club in Florida.

He issued more than 140 pardons and commutations in his final hours in office, including a pardon for his former political adviser, Steve Bannon, who has pleaded not guilty to fraud charges.

But Trump did not issue preemptive pardons for himself or members of his family, after speculation that he might do so.

GRIM MILESTONES

Biden's inauguration caps a five-decade career in public service that included more than three decades in the U.S. Senate and two terms as vice president under former President Barack Obama.

But he faces overlapping crises that will challenge even someone of his political experience.

The pandemic in the United States reached a pair of grim milestones on Trump's final full day in office on Tuesday, reaching 400,000 U.S. deaths and 24 million infections - the highest of any country. Millions of Americans are out of work because of pandemic-related shutdowns and restrictions.

Biden has vowed to bring the full weight of the federal government to bear on the crisis.

His top priority is a $1.9 trillion plan that would enhance jobless benefits and provide direct cash payments to households. It will require approval from a deeply divided Congress, where Democrats will hold slim advantages in both the House and Senate.

Wednesday's executive actions, by contrast, are intended to advance Biden's priorities without the need for legislation.

Full coverage for Eikon readers of the U.S. presidential transition 

For multimedia coverage please open in a separate browser 

(Reporting by Trevor Hunnicutt and Jarrett Renshaw in Washington and Joseph Ax in Princeton, New Jersey; Additional reporting by Jeff Mason, Steve Holland, Will Dunham; Editing by Soyoung Kim, Frances Kerry and Alistair Bell)