Barack Obama, the multiracial son of a mother from Kansas and a father from Kenya, was elected Tuesday as the 44th president of the United States, writing a remarkable new chapter in American history with a campaign built on the theme of hope.

In a race that captivated the nation, and that climaxed in the gloom of an economic crisis, the closing of polls on the West Coast showed that what began as the Illinois senator's "improbable quest" nearly two years ago ended as a commanding electoral victory over Republican John McCain. The Arizona senator had struggled to defy the pollsters in the waning hours of the longest and most expensive presidential election ever.

"If there is anyone out there who still doubts that America is a place where all things are possible, who still wonders if the dreams of our founders are alive in our time, who still questions the power of our democracy, tonight is your answer," Obama told a huge, euphoric crowd in Chicago's Grant Park.

McCain conceded shortly after 10 p.m, saying, "Senator Obama has achieved a great thing for himself and for his country." As he spoke, spontaneous street celebrations erupted among Obama revelers from Los Angeles to Times Square. In Grant Park, tens of thousands of Obama supporters wept, waved flags and chanted, "Yes we did!"

Obama became the first black man to win the presidency, reaching victory by stringing together a series of crucial wins in battleground states, including Florida, Pennsylvania and Ohio.

Obama also scored a decisive victory in Minnesota, the site of the Republican National Convention in September, a time when the state - which hasn't gone Republican in nine presidential elections - was still thought to be up for grabs.

Minnesotans, like voters across the nation, waited in long lines at many polls, with only sporadic reports of polling problems.

Black voters were particularly energized, among them Don Smith, 47, a north Minneapolis man who said he was witnessing one of the most important days in history.

His only regret, he said, was that his mother, who died in August, wasn't there with him.

"I just wish she was alive to see this," said Smith, who was in line to vote before 6 a.m.

Secretary of State Mark Ritchie said that he expected total voter turnout in Minnesota could surpass a record 3 million, more than 80 percent of the roughly 3.7 million eligible voters in the state.

With his running mate, Sen. Joe Biden of Delaware, Obama sought to fend off late Republican efforts to label him as too liberal or too big a gamble for "Joe the Plumber," the Ohio man who came to symbolize white working-class voters coveted by both sides in the election's increasingly bitter endgame.

Recent surveys and exit interviews provided ample evidence that voters went to the polls more uneasy about the economy in the waning days of the Bush administration than about the "culture war" issues such as guns, abortion, and the flag, which traditionally favor Republicans.

There was also evidence that some independent voters were turned off by McCain's running mate, Alaska Gov. Sarah Palin, who electrified the GOP's conservative base with her folksy and oft-lampooned appeals to traditional small-town values.

Obama's victory completed a meteoric rise for a politician who was largely unknown before his speech at the 2004 Democratic convention, and sealed the most calamitous defeat of any Republican presidential candidate since McCain's fellow Arizonan Barry Goldwater in 1964.

End of McCain's long journey

Obama, 47, arrived in Grant Park late in the evening, accompanied by his wife, Michelle, and their daughters, Sasha and Malia.

"Americans have sent a message to the world that we have never been just a collection of individuals, or a collection of red states and blue states, we are and always will be the United States of America," he told the crowd.

A little earlier, after congratulating Obama by phone, McCain, 72, addressed a subdued crowd at the Biltmore Hotel in Phoenix, where he has spent election night in his Senate races.

"We have come to the end of a long journey," McCain said to a smattering of boos. "The American people have spoken, and they have spoken clearly."

Vying to become the nation's first black president, Obama had to overcome months of questions - from Democratic primary opponents as well as Republicans - about his relative inexperience in international affairs. That was in contrast to McCain, a four-term U.S. senator and ex-Navy pilot who was shot down in Vietnam and spent more than five years in a North Vietnamese POW camp.

McCain's status as a war hero and prison camp survivor, combined with his campaign's return from insolvency and disarray before the primaries, fed the GOP's continuing comeback hopes on Tuesday.

Obama, who founded his candidacy on his early opposition to the Iraq war, also faced persistent attacks from conservative detractors about his past associations with his former pastor, the fiery Rev. Jeremiah Wright, and former 1960s radical Bill Ayers.

Throughout the course of the increasingly turbulent election, critics compared him to socialite Paris Hilton and even to Moses, all part of a GOP counterattack against his large rallies, pop-culture status and his inspirational rhetorical stylings.

Transformational candidacy

To Obama's faithful - especially to the youthful volunteers who had signed on during the early, long-shot phase of his candidacy -- the spindly hero of hip-hop culture represents a transformational 21st century leader who can change politics and move the nation beyond the racial and cultural divides of the past.

His election came a day after the death of Madelyn Dunham, his maternal grandmother, who was white, who raised him. Obama took time off from the campaign trail two weeks ago to visit her on her deathbed in Hawaii.

In victory, Obama was buoyed by a huge outpouring of support from young and black voters, even though Obama avoided race as a central plank in his campaign.

While McCain labored over the last weekend to assure his supporters that he was narrowing the gap, Obama's biggest worry had seemed to be overconfidence. In the end, his hope was vindicated.

Staff writer Mitch Anderson contributed to this report.

Kevin Diaz • 202-408-2753