ST. PAUL, Minn. — Sen. Barack Obama made history last night, taking a step toward his once-improbable goal of becoming the nation's first black president.

Obama declared victory in a sweeping speech that was both conciliatory toward his party rivals and a preview of the tough campaign he will wage in the fall. He took the stage to U2's "Beautiful Day," and then he claimed his party's mantle and his place in history.

"Tonight, Minnesota, after 54 hard-fought contests, our primary season has finally come to an end," he said. "Tonight, I can stand before you and say that I will be the Democratic nominee for president of the United States."

With that, the multiracial crowd of 17,000, young and old, some in head scarves, others in trucker hats and union shirts, cheered. They waved signs, and they lifted their cameras and their voices to chant, "Yes we can! Yes we can! Yes we can!"

"America, this is our moment," the 46-year-old senator and one-time community organizer said in his first appearance as the Democratic nominee-in-waiting. "This is our time. Our time to turn the page on the policies of the past."

His opponent, Hillary Rodham Clinton, maneuvered for the vice presidential spot on his fall ticket without conceding her own defeat.

Clinton praised Obama warmly in an appearance before supporters in New York, although she neither acknowledged his victory in their grueling marathon nor offered a concession of any sort.

Instead, she said she was committed to a unified party, and said she would spend the next few days determining "how to move forward with the best interests of our country and our party guiding my way."

Obama's victory set up a five-month campaign to the general election against Republican Sen. John McCain of Arizona, a race between a first-term Senate opponent of the Iraq war and a 71-year-old Vietnam prisoner of war and staunch supporter of the current U.S. military mission.

And both men seemed eager to begin.

McCain spoke first, in New Orleans, and he accused his younger rival of voting "to deny funds to the soldiers who have done a brilliant and brave job" in Iraq. Americans, he added, should be concerned about the judgment of a presidential candidate who has not traveled to Iraq yet "says he's ready to talk, in person and without conditions, with tyrants from Havana to Pyongyang."

McCain agreed with Obama that the presidential race would focus on change. "But the choice is between the right change and the wrong change, between going forward and going backward," he said.

Obama responded quickly, pausing in his own speech long enough to praise Clinton for "her strength, her courage and her commitment to the causes that brought us here tonight."

As for his general election rival, he said, "It's not change when John McCain decided to stand with George Bush 95 percent of the time, as he did in the Senate last year. It's not change when he offers four more years of Bush economic policies that have failed to create well-paying jobs. ... And it's not change when he promises to continue a policy in Iraq that asks everything of our brave young men and women in uniform and nothing of Iraqi politicians."

SURGE OF SUPPORT

Obama secured the Democratic presidential nomination yesterday after a flurry of endorsements from superdelegates and two final primaries.

Clinton, who waged a fierce campaign to become the first woman nominated for president, told fellow New York lawmakers that she would be open to joining Obama as his vice presidential running mate to help unify the party.

The twin developments came on the final day of the primary-caucus season in what became the most closely contested and memorable Democratic nomination battle of the modern era, a classic marathon of unexpected twists and turns between two candidates who divided the Democratic electorate almost precisely in half until the very end.

In the last two primaries, Clinton won in South Dakota and Obama won in Montana. But even before the votes were counted, Obama was guaranteed enough delegates from the two states to ensure that he would obtain the 2,118 threshold required for the nomination.

Saying she understands "that a lot of people are asking, what does Hillary want," Clinton said her goals have not changed since the start of the campaign: an end to the war, universal healthcare and a better economy. Then, in a message to Obama and other Democrats, she added: "And I want the 18 million people who voted for me to be respected, to be heard and no longer to be invisible."

AGAINST THE ODDS

Elected to the U.S. Senate in 2004 after eight years in the Illinois Senate, Obama, the son of a black Kenyan father and a white American mother who was raised in Indonesia and Hawai'i, accomplished something that few thought possible when he launched his candidacy in February 2007 against the heavily favored Clinton.

Clinton, the former first lady and a second-term senator from New York, seemingly held all the advantages, including a vast network of fundraisers, a web of political supporters in virtually every state, and the allure of being able to restore to power a family that had given the Democrats control of the White House for eight years under her husband.

Obama proved to be an even more prodigious fundraiser, tapping the Internet as no candidate ever had to raise millions more than his rival, and also grabbed hold of a powerful movement of grass-roots supporters and volunteers who helped fuel his candidacy and provided a built-in base of organization across the country.

He also tapped effectively into a hunger for change after eight years of the Bush administration. In a Democratic campaign that, initially at least, was cast as experience vs. change, Obama proved to have found the more powerful message.

Obama's victory — and Clinton's unexpected third-place finish — in the Iowa caucuses in January upended expectations for the nomination battle and set the candidates on an epic struggle that continued until the polls closed last night.

With an 11-contest winning streak in mid-February, Obama built what turned out to be an insurmountable lead in pledged delegates, then held on in the campaign's last three months as Clinton ticked off victories in states such as Ohio, Pennsylvania, West Virginia, Kentucky and Indiana.

Meanwhile, Obama effectively turned the tables on Clinton among the party officials and elected officials who make up the nearly 800 superdelegates. After Clinton built a substantial lead among that group in the early stages of the race, Obama steadily gained ground and then surged ahead with these party insiders. Once that began, Clinton's hopes of winning the nomination effectively came to an end.

ON TO THE NEXT STAGE

The last day of the primary-caucus season provided a fitting conclusion to the long nomination battle. It was a day of extraordinary drama, frenzied speculation and fast-changing events. Obama's campaign furiously pressured uncommitted superdelegates to endorse him, Clinton's campaign struggled to provide her with time to leave the race on her own terms, and the media breathlessly sought to keep pace.

Throughout the day, a steady stream of superdelegates declared for Obama, including Rep. Maxine Waters, an ardent Clinton backer. Former President Carter also announced his intention to support Obama.

But it was delegates from South Dakota and Montana who put him over the top, allowing him to say last night that it was ordinary voters who brought him to this moment and will carry him forward.

"The journey will be difficult. The road will be long. But I also face it with limitless faith in the capacity of the American people. Because if we are willing to work for it, and fight for it, and believe in it, then I am absolutely certain that generations from now, we will be able to look back and tell our children that this was the moment when we began to provide care for the sick and good jobs to the jobless," he said. "... This was the moment when we ended a war and secured our nation and restored our image as the last, best hope on earth."

With the end of his speech, the crowd, on its feet by now, roared, clapped and danced.

The Los Angeles Times, Washington Post, McClatchy-Tribune News Service and Associated Press contributed to this report.