By Jeff Mason and Ross Colvin
WASHINGTON (Reuters) - Barack Obama prepared to make history on Tuesday as the first black U.S. president, riding a wave of hope in America and the world as he tackles the worst economic crisis in 70 years and two wars.
Hundreds of thousands of people, bundled up against the cold and in a festive mood, packed Washington's Mall, which stretches 2 miles (3 km) from the Capitol to the Lincoln Memorial on the Potomac River, and along Pennsylvania Avenue to the White House.
People lining the streets cheered wildly as a motorcade carrying Obama, his wife Michelle, and President George W. Bush and his wife Laura, made its way to the Capitol from the White House.
Obama, a Democrat, was due to be sworn in on the steps of the Capitol as the 44th U.S. president just before noon EST (5 p.m. British time), taking over from Bush, a Republican.
The inauguration was taking place amid unprecedented security. About 8,000 police were deployed and a total of 32,000 military personnel were on duty or on standby.
The Homeland Security Department said authorities were investigating a potential threat of "uncertain credibility" in connection with the inauguration.
This will be the first inauguration of a new U.S. president since the September 11, 2001, attacks that took place early in Bush's two-term presidency and deeply shaped his policies, prompting Washington's war on terrorism. Obama's election has also stirred white supremacists to anger, sparked arrests during his campaign and raised assassination fears.
Major U.S. stock indexes fell on Tuesday on mounting worries over grim earnings and the health of the banking sector, highlighting the scale of the financial problems Obama will face.
The inauguration of Obama, 47, the son of a black Kenyan father and a white mother from Kansas, will be full of ceremony, and full of symbolic meaning for African-Americans, who for generations suffered slavery and then racial segregation that made them second-class citizens.
LINCOLN'S BIBLE
Obama was set to take the oath of office with his hand on a Bible used by Abraham Lincoln at his first inauguration in 1861, standing on the western steps of the Capitol, a building that was partly built by black slaves.
Some estimates put the number of people expected to pack the Mall and inaugural parade route at more than 2 million. Crowds clogged the city's metro rail system and thronged the security check-points.
"This is chaos now," said Judy Bailey, 42, of Cincinnati, Ohio, as police shunted her further and further away from the swearing-in ceremony early in the morning. "But it is amazing to be here. This is history in the making."
Polls show widespread U.S. public support for Obama and optimism about the coming four years of his presidency, despite a deepening recession that has saddled the country with a $1 trillion (716 billion pound) deficit and 11 million people unemployed.
Bush is leaving office having plumbed record lows in approval ratings.
GETTING DOWN TO WORK
Obama, a former Illinois senator who capped a hard-fought election campaign with a comfortable win against Republican John McCain in November, has stressed that the time to party and celebrate will be short-lived.
On Wednesday he will start shepherding an $825 billion economic stimulus plan through Congress.
He faces daunting challenges -- economic turmoil, the wars in Iraq and Afghanistan, global warming, conflict in Gaza, tensions between Pakistan and India and prickly ties with Russia.
But analysts say that at least for now, it will be his ability to revive the recession-hit economy that will be the benchmark by which his presidency is judged.
The Washington Post reported that in one of his first actions as president, Obama planned to name former Sen. George Mitchell as his Middle East envoy in one of his first actions as the new U.S. president.
Obama will also meet military commanders on Wednesday to discuss the possibility of accelerating the U.S. troop withdrawal from Iraq, to fulfil a campaign pledge to withdraw all troops within 16 months.
He is also expected to discuss the need for more forces in Afghanistan at the White House with a Pentagon delegation led by Defence Secretary Robert Gates and Navy Adm. Mike Mullen, chairman of the U.S. Joint Chiefs of Staff, officials said.
SPEECH
Obama's swearing-in will be followed by the U.S. Marine Corps band playing "Hail to the Chief" and a 21-gun salute. He was then to deliver his eagerly anticipated inauguration speech, expected to last about 20 minutes.
"He is going to lay out a lot of the challenges we face as a country, but he will also remind ... that America has faced great challenges before," his spokesman Robert Gibbs told CNN on Tuesday.
"He will talk about responsibility, particularly the great responsibility in the action of government and financial institutions, some of whose actions have got us into the mess we are in now."
He played down suggestions that Obama could issue executive orders as early as Tuesday to close the U.S. military prison at for foreign terrorism suspects at Guantanamo Bay and repeal a ban on overseas funding for clinics or groups which provide abortion services.
The Guantanamo prison has been a lightning rod for broad world disapproval of many Bush policies in the U.S. war on terrorism.
Gibbs said some announcements would be made later in the week.
(Additional reporting by Jeff Mason, Jim Wolf and Randall Mikkelsen, Writing by Ross Colvin, Editing by Frances Kerry.)
