The White House did not say in advance what Obama's service project would be. In 2009, he helped spruce up a shelter for homeless teens in one of Washington's poorer neighborhoods then visited wounded soldiers at Walter Reed Army Medical Center.
The White House sees the call to service as a way for Americans across the country to honor the memory of Martin Luther King Jr. The day Obama publicly takes the oath of office marks King's birthday, and 2013 is the 50th anniversary of the civil rights leader's March on Washington.
Also Saturday, Michelle Obama and Jill Biden were hosting the Kids' Inaugural Concert, an evening event paying special tribute to military spouses and children.
The crowds pouring into Washington were expected to be far smaller than they were four years ago, and there will be fewer inaugural balls for the president and first lady to attend. Still, Obama's swearing-in at the Capitol is expected to draw up to 800,000 people, which would make it the largest second.
The president was still working on his inaugural address heading into the weekend. He isn't expected to delve deeply into the policy objectives he'll tackle in a second term, but the tone and theme of the speech will set the stage for the policy fights to come.
Aides said he will make the point that while the nation's political system doesn't require politicians to resolve all of their differences, it does require Washington to act on issues where there is common ground. He will speak about how the nation's core principles can still guide a country that has changed immensely since its founding.
Temperatures were forecast to fall throughout the weekend and be in the 30s on Monday when the crowds gather along the parade route that will take Obama from Capitol Hill to the White House.
Despite scaling back on some of the revelry, the inauguration will be a star-studded affair. Top acts including Beyonce, Katy Perry and Brad Paisley have signed on to perform at the weekend's events.
The inauguration also is bringing thousands of Obama campaign staffers and donors to Washington, with many getting invitations for tours and other events at the White House. On Friday, the president and first lady held two private events for donors who helped finance his 2012 campaign.