Washington - Barack Hussein Obama officially began his second term as the 44th president Sunday, setting the stage for him to lay out his vision in an inaugural address on the anniversary of Martin Luther King Jr.'s birthday.

More than half a million people are expected to watch from the Mall, four years and a day after the nation's first African-American president was sworn in the first time.

President Obama, joined on Sunday by a dozen family members, recited the 35-word oath of office administered by Chief Justice John Roberts in the Blue Room of the White House. It was an intimate and businesslike 30 seconds of history. Obama's hand rested on a Bible that the first lady's father, Fraser Robinson, had given to his mother, LaVaughn Delores Robinson, on Mother's Day 1958.

The president saved the pomp for today, when he and Roberts will repeat the oath outside the U.S. Capitol. The Constitution mandates that presidential terms begin Jan. 20, and when the date falls on a Sunday, the public ceremony traditionally is held the next day.

Organizers said the crowd will be far smaller than the estimated 1.8 million who were there in 2009 for an emotional and historic gathering on a bitterly cold day. But the stakes for Obama are no less important as he delivers his second inaugural address at a time when the economy remains fragile and his signature achievements, including health care reform, are still works in progress.

Obama, who has confessed to feeling bruised by the partisanship in Washington, aims to use his remarks to underscore the importance of seeking common ground in Washington and encourage Americans to engage in the political process, White House senior adviser David Plouffe said.

These are themes that echo the grass-roots activism that King, born 84 years ago, put to use so effectively during the civil rights movement.

"He's going to make that point very strongly - that people here in Washington need to seek common ground," Plouffe said of Obama on "Fox News Sunday."

After reciting the oath on Sunday, Obama kissed first lady Michelle Obama and their daughters, Malia and Sasha. "I did it," the president said.

"You didn't mess up," Sasha said, a reference to four years ago when Roberts and Obama bungled the oath at the public ceremony and had to do it again privately to make sure all constitutional obligations were met.

By today, Obama will have taken the oath four times - as many times as President Franklin D. Roosevelt. The last president to take the oath on a Sunday was Ronald Reagan, as he began his second term.

The brief swearing-in ceremony at the White House - from the family's entrance to the handshakes and kisses that marked departure - took less than 90 seconds and provided one of several glimpses Sunday of the 51-year-old president. He also laid a wreath at the Tomb of the Unknowns at Arlington National Cemetery and worshiped at a celebrated African-American church.

The Obamas began the day in the second row of the District's Metropolitan African Methodist Episcopal Church- known as the "national cathedral of African Methodism"- where the crowd sang "Happy Birthday" to the first lady, who turned 49 on Thursday.

Metropolitan's pastor, the Rev. Ronald Braxton, invoked the Obama re-election slogan of "Forward," in his sermon, based on Exodus Chapter 14.

Braxton recalled the Old Testament account of Moses and the Israelites as they fled persecution and confronted the Red Sea in their path. "The people couldn't turn around. The only thing that they could do was to go forward," said Braxton.

"Mr. President. . . never let fear blind you of the power, potential and possibilities that rest only in the hands of God," Braxton said.

Vice President Joe Biden got a jump on the president by taking his oath at an 8:21 a.m. ceremony at his residence at the Naval Observatory. Justice Sonia Sotomayor did the honors, becoming the fourth woman and the first Hispanic to administer the oath to the president or vice president.

If Obama's swearing-in was private and quick, Biden's was more of a party, attended by more than 120 people. The timing of the event apparently was driven by Sotomayor's need to be in New York for an afternoon address and book-signing for her new memoir.

Washington began to play its quadrennial role as the host of inaugural hoopla: red, white and blue bunting draped hotels and official buildings; bleachers lined the parade route along Pennsylvania Avenue; five Jumbotrons and 1,500 portable toilets sprouted across the Mall; out-of-towners in parkas and sneakers mingled with people wearing gowns and heels.

Visitors and the hundreds of workers preparing for the public ceremony were blessed with temperatures at least 10 degrees warmer than the high 30s to low 40s forecast for today.

Today's ceremony will feature an original poem from Richard Blanco, who will be the youngest inaugural poet and the first Latino to serve in the role. Kelly Clarkson, James Taylor and Beyonce will perform.

After his address, Obama will dine with members of Congress at a luncheon on the Hill, a tradition that can be traced back to 1897 and the inauguration of President William McKinley. After the luncheon, Obama will review a military procession and then lead the inaugural parade from the Capitol to the White House, where he will watch from a reviewing stand.

The parade, which is scheduled to begin at 2:30 p.m., will unfold between a military cordon of about 1,500 service members. Planners expect about 10,000 to march, including bands, military units, equestrian teams and other organizations representing all 50 states.

Then come two official inaugural balls, both of which will be held at the Walter E. Washington Convention Center. The lineup of talent includes Alicia Keys, Usher and Soundgarden.

The Obamas are expected to appear at the Inaugural Ball and the Commander-in-Chief Ball. Inauguration planners made some tickets to the Inaugural Ball available to the public, but the Commander-in-Chief's Ball, which began with President George W. Bush, is open only to invited members of the military.

Layers of security, though scaled back from 2009, will close down or restrict access to large parts of downtown Washington. The Secret Service, which is coordinating the effort among civilian law enforcement, National Guard and military personnel, started closing streets at 7 a.m. Sunday, beginning with Pennsylvania Avenue between Second and 15th streets NW. Today, an estimated 6,000 members of the National Guard, representing 25 states and territories, will assist, mostly with crowd control.

But even before the big day, thousands of well-wishers clogged Pennsylvania Avenue and the Mall on Sunday, seeking an opportunity to soak up history on a sunny afternoon. Many were first-time inaugural visitors, eager for a chance to catch a glimpse of the president or get a prime viewing spot near the big screens on which the swearing-in and speech will be broadcast live.

Outside the White House, Louphelia Simmons and April Robinson marveled at what was to come. Simmons had stayed home in Birmingham, Ala., four years ago. She was not happy, but family obligations prevented her from making the trip.

This year, Simmons said she obtained tickets from Rep. Terri Sewell, D-Ala., and was determined to be in Washington.

"I want to be part of this historic moment," Simmons said. "Never did I think that I would see this in my lifetime."