WASHINGTON — Barack Obama took the oath of office as 44th president of the United States today facing twin challenges of war and recession and an electorate that believes he's up to the task.

The nation's first black president also will face something more immediately imposing: a crowd that could exceed the record 1.2 million from Lyndon Johnson's inauguration in 1965, dotting the National Mall and lining the Pennsylvania Avenue parade route to the White House.

Then there will be the ghosts of presidents and preachers past: Abraham Lincoln, whose Bible will be used for the first time since his presidency. Franklin Roosevelt, the last incoming president to face an economy is such disarray. John F. Kennedy, whose youth and relative inexperience Obama shares. And Martin Luther King Jr., whose 80th birthday was celebrated yesterday; he was assassinated when Obama was 6.

Center stage will be Obama, the son of a Kenyan father and a mother from Kansas, who rose from the obscurity of the Illinois state Senate in 2004 to the most powerful job in the world.

"What an incredible testimony this is to both him and to the possibilities of America," said Yale political science professor Stephen Skowronek. "There is no historical parallel."

Obama, 47, took the oath of office at noon — 7 a.m. Hawai'i time — from Chief Justice John Roberts, who at 53 also represents a new generation of American leadership. Vice President-elect Joe Biden will be sworn in by Justice John Paul Stevens, the court's senior member.

The inauguration simultaneously marks the end of George W. Bush's eight-year tenure at the White House and Obama's nearly two-year quest to take his place — one that moved from quixotic to complete as the man who came to be known as "No-drama Obama" bested Democrat Hillary Rodham Clinton and Republican John McCain.

Since winning about 67 million votes on Election Day for a 53 percent mandate, Obama has chosen a centrist Cabinet, paused briefly for a Hawai'i vacation and jumped with both feet into the two biggest economic issues facing the nation. Last week, he won congressional authority to use the second half of a $700 billion financial industry rescue plan. Next month, he hopes to win $825 billion or more in spending increases and tax cuts.

Americans have high expectations. A majority of those surveyed in a USA Today/Gallup survey last week predicted that Obama will be able to achieve every one of 10 major campaign promises, from reducing healthcare costs and increasing coverage to withdrawing most U.S. combat troops from Iraq within 16 months.

Yesterday, Obama spent his last day as president-elect visiting injured troops, performing community service projects and hosting three bipartisan dinners to honor Biden, McCain and former Secretary of State Colin Powell. He switched from dark gray jeans, shirtsleeves and a paintbrush to a black tuxedo and long black tie.

"After the season of campaigning has ended, each of us in public life has a responsibility to usher in a new season of cooperation built on those things we hold in common — not as Democrats, not as Republicans, but as Americans," he said at the McCain event. "Let us strive always to find that common ground, and to defend together those common ideals, for it is the only way we can meet the very big and very serious challenges that we face right now."

Obama's relatively brief inauguration speech was ready for delivery. Today it goes into the history books, and the man known for being an eloquent speaker turns to governing.

"I am making a commitment to you as the next president that we are going to make government work," he said yesterday. "But I can't do it by myself. ... We're going to have to take responsibility, all of us."