WASHINGTON – Before a jubilant crowd of more than a million, Barack Hussein Obama claimed his place in history as America’s first black president, summoning a dispirited nation to unite in hope against the “gathering clouds and raging storms” of war and economic woe.

On an extraordinary day in the life of America, people of all colors and ages waited for hours Tuesday in frigid temperatures to witness a young black man with a foreign-sounding name take command of a nation founded by slaveholders. It was a scene watched in fascination by many millions – perhaps billions – around the world.

“We gather because we have chosen hope over fear, unity of purpose over conflict and discord,” the nation’s 44th president said.

The presidency passed to Democrat Obama from Republican George W. Bush at the stroke of noon, marking one of democracy’s greatest gifts: the peaceful transfer of power.

But it was a stark transfer all the same. In one of the new administration’s first acts, Obama ordered federal agencies to halt all pending regulations until further review – this after Bush’s final weeks raised heated debate over rushing new rules into effect on the way out the door.

And even though new White House aides struggled to find offices and work intercoms, an overhauled www.whitehouse.gov Web site was running under Obama’s banner within minutes of his swearing-in. “Change has come to America,” it declared.

Obama plunges into his new job in earnest on Wednesday after capping inaugural festivities at a national prayer service in the morning, meeting with his economic team and Iraq advisers and welcoming a stream of public visitors into the White House while Congress gives his economic revival plan a going-over and takes up the nomination of Hillary Rodham Clinton to be secretary of state. Her confirmation has been held up for now by Republican concern over the foundation fundraising of her husband, the former president.

The new president had been buoyant and relaxed through the three days of preinaugural festivities.

But he seemed somber as he stood on the Capitol steps, placed his left hand on the Bible used by Abraham Lincoln and repeated the inaugural oath “to preserve, protect and defend” a Constitution that originally defined blacks as three-fifths of a person. A deafening cheer went up.

“What is required of us now is a new era of responsibility – a recognition, on the part of every American, that we have duties to ourselves, our nation, and the world, duties that we do not grudgingly accept but rather seize gladly,” Obama said. “This is the price and the promise of citizenship.”

Throughout his inaugural address, an 18-minute sermon on civic duty, Obama wove a thread of personal responsibility and accountability. A liberal Democrat proposing billions of dollars in new spending, Obama nonetheless spoke of the limits of government.

“It is the kindness to take in a stranger when the levees break, the selflessness of workers who would rather cut their hours than see a friend lose their job which sees us through our darkest hours,” he said. “It is the firefighter’s courage to storm a stairway filled with smoke, but also a parent’s willingness to nurture a child, that finally decides our fate.”

Obama’s 10-year-old daughter, Malia, aimed a camera at her father as he spoke. Michelle leaned onto the edge of her seat, body tensed and brow knitted.

“Starting today, we must pick ourselves up, dust ourselves off and begin again the work of remaking America,” Obama said.

The day’s high spirits were jarred by sudden concern about the health of Sen. Edward M. Kennedy. The legendary Democrat, suffering from brain cancer, was rushed from a Capitol luncheon in Obama’s honor to a hospital.

Later, Sen. John Kerry of Massachusetts said Kennedy was laughing and joking at the hospital and itching to get back to work.

On the inaugural parade route, Obama and his wife, Michelle, climbed out of the heavily armored presidential limousine and walked a few blocks along famed Pennsylvania Avenue, waving to crowds under the watchful eyes of security agents.

Hours later, they put the day’s formality behind them to swirl through 10 inaugural balls. With the president in white tie and the first lady in a white one-shouldered gown, their first dance was to Beyonce singing the Etta James classic “At Last.”

“Tonight, we celebrate. Tomorrow, the work begins,” Obama said at the Commander in Chief Ball.

Alan Fram, Donna Cassata, Gillian Gaynair, Ricardo Alonso-Zaldivar, Kevin Freking, Ed Tobias, Ben Evans, Seth Borenstein and H. Josef Hebert contributed to this report