WASHINGTON (AP) -- His second term already under way, President Barack Obama aims to set an optimistic tone when he takes the oath again to lead a divided nation seeking solutions to economic woes at home and conflict overseas.

Hundreds of thousands are expected to gather on the National Mall to witness Obama's swearing in and inaugural address Monday. The celebrations will extend across the nation's capital, including the traditional inaugural parade and a pair of glitzy formal balls.

With January 20 falling on a Sunday meant that Obama would end up being sworn in for his second term twice. Sunday's ceremony was an intimate gathering at the White House with only a dozen family members on hand to witness Chief Justice John Roberts administer the oath of office.

Today in his inaugural address to the crowd in Washington and millions more watching on television, Obama will urge lawmakers to find common ground when they can, and preview his second term goals, including comprehensive immigration reform, stricter gun control laws, and an end to the war in Afghanistan.

"What the inauguration reminds us of is the role we have as fellow citizens in promoting a common good, even as we carry out our individual responsibilities that, the sense that there's something larger than ourselves, gives shape and meaning to our lives," Obama said, previewing his address during brief thank-you remarks to donors at a reception Sunday night.

The mood surrounding Obama's second inaugural is more subdued than it was four years ago, when the swearing in of the nation's first black president drew 1.8 million people to the Mall. Still, organisers were expecting up to 700,000 to attend Monday's events, which would make it the largest second-term inaugural in history.

The weather forecast was encouraging, to a point. High temperatures were predicted for the lower 40s during the day, with a slight chance of rain and snow showers in the afternoon and flurries later.

Security was tight across Washington, with several streets near the White House and Capitol Hill closed off. Humvees and city buses were being used to block intersections.

David Richardson of Atlanta and his two young children were among the early crowds heading to the National Mall Monday even before sunrise.

"We wanted to see history, I think, and also for the children to witness that anything is possible through hard work," Richardson said.

Wendy Davis of Rome, Georgia was one of thousands of inaugural attendees who packed Metro trains before sunrise headed for the Capitol and parade route. Davis came four years ago as well but was among the many ticketholders who couldn't get in because of the massive crowds. She was determined to get in this time.

"I thought I was early last time but I obviously wasn't early enough," she said.

The president was officially sworn-in shortly before noon on Sunday, in keeping with the Constitution's mandate that presidents begin their new term on January 20. But because inaugural ceremonies are historically not held on Sundays, the public celebration was pushed to Monday, coinciding with the birthday of late civil rights leader Martin Luther King Jr.

The president and his family will begin their day at a morning church service before heading to the Capitol for the swearing-in. Obama will attend the traditional luncheon with lawmakers before joining marching bands and floats in the inaugural parade, which winds its way from Capitol Hill to the White House.