WASHINGTON (AP) — Two days from the White House, President-elect Barack Obama joined a vast throng Sunday at a joyous pre-inauguration celebration staged among marble monuments to past heroes. "Anything is possible in America," declared the man who will confront economic crisis and two wars when he takes office.

"Despite the enormity of the task that lies ahead, I stand here today as hopeful as ever that the United States of America will endure — that it will prevail, that the dream of our founders will live on in our time," the president-elect said at the conclusion of a musical extravaganza that featured U2, Beyonce, Bruce Springsteen and a host of other stars.

Obama and his family held the seats of honor at the event, and a crowd of tens of thousands spilled from the base of the Lincoln Memorial toward the Washington Monument several blocks away in the cold, gray afternoon of mid-January.

It was the high point of a full day of pre-inaugural events that included a wreath-laying at the Tomb of the Unknowns at Arlington National Cemetery and a morning church service where children recalled the life of civil rights leader Martin Luther King Jr.

Obama's motorcade drew ever-larger crowds as the day wore on and he and his wife, Michelle, and their children Sasha and Malia crisscrossed the city.

"Just another typical Sunday," deadpanned the Rev. Derrick Harkins, pastor at the Nineteenth Street Baptist Church, where the soon-to-be first family prayed.

Of course it was anything but — a run-up, in fact, to the first inauguration of an African-American president in a nation founded by slave-owners.

Obama's aides said he was readying an inaugural address that would stress twin themes of responsibility and accountability, and they predicted he would devote his first week in office to economic recovery, setting in motion a 16-month troop withdrawal from Iraq and decreeing a code of ethics for his administration.

With the economy weak and growing weaker, banks in trouble and joblessness rising, Obama's team was careful to warn against any expectation that he would be a miracle worker once in office. "I think it's fair to say that it's going to take not months but years to really turn this around," said David Axelrod, a political strategist expected to have White House space mere paces from the Oval Office.

Obama said as much in his own brief remarks. "I won't pretend that meeting any one of these challenges will be easy. It will take more than a month or a year, and it will likely take many," he said.

He stood alone at the base of the steps before the statue of a seated Lincoln looking out at a crowd every bit as large as the one King addressed a generation earlier in his "I have a dream" speech that was a defining moment of the civil rights era.

An even larger audience is forecast for the inauguration outside the Capitol on Tuesday, with estimates running into the millions. Agencies in charge of logistics and security said they would enforce a ban on personal auto traffic across the Potomac River bridges from Virginia into Washington and seal off a large portion of the downtown area. Access to buildings along the Inaugural parade route down Pennsylvania Avenue was limited to those who gained Secret Service approval in advance.

Obama's day began at the Tomb of he Unknowns at Arlington National cemetery, where he and Vice President-elect Joseph Biden laid a wreath in memory of fallen heroes. The two men placed their hands over their hearts as a uniformed bugler played taps in a somber opening to a festive day.

The scene was quite different at the church a few miles away, where the congregation erupted in applause when Obama and his family walked to their seats.

"Understand that God has prepared you, and God has placed you, and God will not forsake you," Harkins told the incoming president.