President-elect Barack Obama began moving Wednesday to build his administration and make good on his ambitious promises to point the United States in a different direction, as his commanding victory reordered the American political landscape and transfixed much of the nation and the world.

A day after becoming the first African-American to capture the presidency, Mr. Obama announced a transition team and prepared to name an ally as his White House chief of staff in his first steps toward assuming power. President Bush vowed to work closely with Mr. Obama to ensure a smooth transition in the first handover since the attacks of Sept. 11, 2001.

Representative Rahm Emanuel of Illinois, the fourth-ranking House Democrat and a close friend of Mr. Obama’s from Chicago, has been offered the job of chief of staff, and although he was said to be concerned about the effects on his family and giving up his influential role on Capitol Hill, many Democrats said they expected him to accept it. Mr. Obama named John D. Podesta, the former Clinton White House chief of staff, to lead his transition team along with Valerie Jarrett, a longtime adviser, and Pete Rouse, his Senate chief of staff.

In turning to Mr. Emanuel and Mr. Podesta, Mr. Obama sought out two of the hardest-hitting veterans of President Bill Clinton’s administration, known for their deep Washington experience, savvy and no-holds-barred approach to politics. Neither is considered a practitioner of the “new politics” that Mr. Obama promised on the campaign trail to bring Republicans and Democrats together, suggesting that the cool and conciliatory new president is determined to demonstrate toughness from the beginning.

Mr. Obama stayed largely out of sight on Wednesday as Democrats counted their gains and Republicans stewed over what went wrong. The scope of his success underscored the nation’s discontent with Mr. Bush’s presidency. Mr. Obama captured an estimated 52 percent of the popular vote and 349 electoral votes to John McCain’s 46 percent and 162 electoral votes, with Missouri and North Carolina still too close to call.

Mr. Obama also ushered in a wave of Democrats who strengthened his party’s hold over Congress, picking up at least five seats in the Senate and 19 in the House. Republican senators in Alaska, Minnesota and Oregon were still clinging to razor-thin leads, including Ted Stevens of Alaska, fresh from his conviction on seven felony counts of failing to disclose $250,000 in gifts and services he received.

But the crowds had barely drifted out of Grant Park in Chicago after an exuberant late-night celebration of Mr. Obama’s triumph before the rising sun brought fresh signs of the daunting burdens to come.

In Russia, President Dmitri A. Medvedev warned that he would deploy missiles if Mr. Obama built Mr. Bush’s planned missile defense system in Eastern Europe. In Afghanistan, President Hamid Karzai pleaded with Mr. Obama to halt air strikes that have been killing civilians. And in the United States, stock markets plunged again amid more dark economic news.

Still, the phenomenon of a black president of the world’s most powerful nation captured public imagination in many quarters of the globe. Supporters in many cities in the United States chanted in the street and large crowds gathered at the headquarters of newspapers such as The New York Times and The Washington Post seeking sold-out copies of historic front pages.

The Congressional committee that puts together the inauguration ceremonies announced that the theme would be “A New Birth of Freedom,” to mark the 200th anniversary of Abraham Lincoln’s birth, symbolically linking one president from Illinois who freed the slaves to another who broke the ultimate racial barrier in politics.

Even the departing Bush team recognized the power of the moment. “It will be a stirring sight to watch President Obama, his wife, Michelle, and their beautiful girls step through the doors of the White House,” Mr. Bush told reporters in the Rose Garden. “I know millions of Americans will be overcome with pride at this inspiring moment that so many have awaited for so long.”

Secretary of State Condoleezza Rice made a surprise appearance at her department’s daily briefing to congratulate Mr. Obama.

“As an African-American, I am especially proud because this is a country that’s been through a long journey in terms of overcoming wounds and making race not the factor in our lives,” Ms. Rice said. “That work is not done, but yesterday was obviously an extraordinary step forward.”

The election proved so invigorating to the American public that turnout climbed to its highest rate in 44 years. Although experts differed in their projections as provisional and absentee ballots are counted, Michael McDonald, a voting expert at George Mason University, estimated that 133.3 million people had voted, eclipsing the 123 million who participated four years ago. That amounted to 62.6 percent of all eligible voters, just shy of the 62.8 percent in 1964.

With the election now behind them, the Bush and Obama teams began the delicate 77-day transition until inauguration. The General Services Administration turned over 120,000 square feet of office space in downtown Washington to the Obama transition team and select Obama advisers were due to be given interim security clearances.

Mr. Obama and Vice President-elect Joseph R. Biden Jr. will receive briefings Thursday from Mike McConnell, the director of national intelligence, and thereafter each morning by a pair of Central Intelligence Agency officials. Mr. Obama was given brief updates during the campaign, but aides said the sessions now would resemble the presidential daily briefing presented to Mr. Bush each morning.

Beyond choosing staff members, Mr. Obama must decide how active he intends to be in asserting leadership during the transition. Mr. Obama has conferred with Congressional leaders about passing a $100 billion economic stimulus package in a lame-duck session the week of Nov. 17 to pay for public works projects, aid to cities and states, and unemployment, food stamp and heating benefits.

But Congressional aides said that if Mr. Obama could not win agreement from Mr. Bush and Senate Republicans, they might scale the package back to about $60 billion, then come back in January with a broader plan.