WASHINGTON - Democrat Barack Obama, fresh from a historic election win as the U.S.'s first black president, turned Wednesday to the sobering challenge of steering a new course for a country grappling with two wars abroad and the threat of a prolonged recession at home.

Obama easily defeated Republican John McCain in a triumph that reflected Americans' weariness with eight years of Bush administration rule.

His first task will be to begin building - over the next 2 1/2 months - a Democratic administration that will help him make good on the promises of change that carried him to the White House.

Obama was expected to take much of Wednesday off. But he was also to name Illinois Congressman Rahm Emanuel as his chief of staff Wednesday, aides told the Associated Press on condition of anonymity ahead of the announcement. On Thursday, top intelligence officials are scheduled to begin meeting with Obama for classified daily briefings.

Obama's speech before 240,000 supporters on election night clearly acknowledged the difficulties - domestic and international - he will face.

"We know the challenges that tomorrow will bring are the greatest of our lifetime - two wars, a planet in peril, the worst financial crisis in a century," Obama said. "

"We may not get there in one year or even in one term," he said. "But, America, I have never been more hopeful than I am tonight that we will get there. I promise you, we as a people will get there."

In electing Obama, the son of black man from Kenya and a white woman from Kansas, American voters broke with the country's sad history of racial divisions.

It was an accomplishment recognized both by supporters and by McCain who, in conceding defeat, acknowledged the "special pride" black Americans must be feeling Tuesday night.

"Change has come to America," Obama, the son of black man from Kenya and a white woman from Kansas, told cheering supporters in Chicago.

Obama tore up the U.S. political map in triumphing over McCain, a veteran Republican senator who was saddled with President George W. Bush's legacy. Toward the end of his presidency, Bush was almost as unpopular at home as he is abroad.

Key American allies were quick to welcome Obama's election, which some in Europe compared to man's first steps on the moon and the fall of the Berlin Wall.

"At a time when we have to confront immense challenges together, your election raises great hopes in France, in Europe and in the rest of the world," French President Nicolas Sarkozy said in a letter to the president-elect.

Germany's Chancellor Angela Merkel said she expects "closer and more trusting cooperation between the United States and Europe" under Obama's leadership.

Obama's choice as vice president, Sen. Joseph Biden, predicted during the campaign that as president, Obama would be tested by a foreign power.

Russia on Wednesday signaled that it may be first to do so, with President Dmitry Medvedev saying his country would deploy short-range missiles close to its borders with NATO countries Poland and Lithuania, in response to U.S. plans for a missile defense system in Europe.

Medvedev, in a speech, blamed the U.S. for the global financial crisis and for allegedly provoking Russia's war with Georgia in August.

He also sent a congratulatory telegram saying there is "solid positive potential" for the election to improve strained relations between Washington, but only if Obama engages in constructive dialogue.

When Obama takes office Jan. 20 as the 44th U.S. president, he may face more difficult challenges both at home and abroad than any new U.S. president since the Great Depression.

But he will do so with many allies in Congress, as the Democrats expanded their majorities in both the U.S. House and Senate. And he will take office with broad popular support.

With most U.S. precincts tallied, Obama clinched 52.3 percent of the popular vote compared to 46.4 percent for McCain. That made him the first Democrat to receive more than half of the popular vote since Jimmy Carter in 1976.

In the state-by-state contest that, under the U.S. constitution, determines the presidency, Obama needed only 270 votes to win. He sailed to victory with 349 to McCain's 147, with three states still too close to call.

Voter turnout, still being counted, was expected to shatter records.

Supporters welcomed Obama's victory with delirious celebrations in cities across the U.S. and abroad. In Washington, hundreds took to the streets near the White House, carrying balloons, banging drums and chanting "Bush is gone!"

Prominent black leaders were overjoyed, weeping unabashedly in public.

From Hong Kong, retired Gen. Colin Powell, a black Republican, called the senator's victory "a very very historic occasion," and predicted that Obama would be "a president for all America."

Obama's victory marked the rise of a new generation of American leadership, after 16 years of presidents who came of age during the Vietnam War era. Obama. 47, was still a child when most U.S. troops came home.

It was also Americans' final, symbolic rejection of Bush's presidency. The incumbent saw his popularity plummet with his administration's bungled response to Hurricane Katrina in 2005, the war in Iraq, and to the regulatory lapses that many think led to the U.S. financial crisis.

The race was the longest, most expensive and most riveting in memory. Both Obama and McCain had been on the campaign train for almost two years.

McCain called his former rival to concede defeat, telling disappointed supporters that Americans have "spoken, and spoken clearly."

But, after a fiercely negative campaign, he pledged to support Obama and "do all in my power to help him lead us through the many challenges we face."

Bush pledged on Wednesday "complete cooperation" in the transition and called Obama's victory a "triumph of the American story."

Obama is expected to bring a new style and tone in American foreign policy.

He has said he will try to withdraw U.S. troops from Iraq in 16 months and has called for reaching out to adversaries, such as Iran and Cuba. He has urged the closing of the Guantanamo Bay prison and favors cap-and-trade systems to reduce global warming.

Internationally, Obama is hugely popular. Part of his appeal is his multicultural heritage: Besides his Kenyan father, he has a half-sister who is the daughter of an Indonesian.

In his campaign, Obama mined a deep vein of national discontent with the status quo. He promised to heal divisions and end the partisan rancor that marks American politics, while building a phenomenal political organization and waging a nearly flawless 21-month campaign for the White House.

He first soared into the national spotlight with his electrifying speech at the 2004 Democratic National Convention, when he made his first run for the Senate. He offered a message of unity to a country mired in partisan anger.

Throughout his campaign, Obama was the target of false rumors about his religion, his ethnicity and his patriotism.

McCain, 72, was a tough rival for Obama. He is widely admired for his enduring 5½ years as a prisoner of war during the Vietnam War. His reputation as a maverick gave Republicans hopes of winning over independents and moderate Democrats.

He tried without success to portray Obama as too radical and inexperienced, casting him as an advocate of high taxes and socialism. And, while McCain's choice for running mate, Alaska Gov. Sarah Palin, energized much of the Republican base, her lack of experience and poor performance in interviews worried many voters.