The Illinois senator's giant-killing win over Hillary Clinton -- who refused formally to concede -- came at the climax late Tuesday of the longest, most expensive and spellbinding nominating epic ever.

 

Dominating newspaper front-pages across the world, Obama declared to 19,000 baying supporters in St. Paul, Minnesota: "America, this is our moment.

 

"This is our time. Our time to turn the page on the policies of the past," the 46-year-old Chicagoan declaimed, tweaking the Republicans by speaking at the venue of their presidential convention in September.

 

"Tonight, I can stand before you and say that I will be the Democratic nominee for president of the United States," he said in his victory speech.

 

Obama's momentous victory, five months since his shock win over Clinton in the very first nominating contest in Iowa, set up an intriguing general election clash with McCain, the 71-year-old Republican senator from Arizona.

 

On November 4, voters must pick between Obama, a freshman senator and charismatic mixed-race standard-bearer of a new political generation, and McCain, a wounded Vietnam war hero asking for one final call to service.

 

Well ahead of the election, Obama has a slight edge over McCain, 46.6 - 45.2 percent, in an average of national opinion polls by RealClearPolitics.com, with their battle already boiling over Iraq, whether to talk to US enemies like Iran, and the ailing US economy.

 

Both Obama and Clinton were due Wednesday to address an influential pro-Israel lobbying group in Washington, giving the new presumptive nominee a chance to stake out his appeal for a new diplomacy in the Middle East.

 

Aides to the two Democrats declined to say if they might meet privately on the sidelines of the Washington conference, after Clinton told New York lawmakers that she was open to serving as Obama's vice presidential nominee.

 

"The vice presidential process is a serious process that will begin in earnest now, as we have become the presumptive nominee," Obama's communications director Robert Gibbs told NBC television early Wednesday.

 

"I feel confident in saying that this party will be unified in moving forward, to make sure we have a Democratic president come November," he said.

 

Clinton, thwarted in her own historic quest to be the first female president, refused to explicitly admit defeat and said she would consult with supporters and party leaders "in the coming days" on the way forward.

 

Occasionally elegiac but more often defiant in her own speech at a Manhattan sports college, Clinton described how every one of her nearly 18 million votes had felt like "a prayer for the nation."

 

Failing an outright concession from the New York senator, the Democratic Party's seniormost figures are reportedly set to go public with an appeal to the last undeclared "superdelegates" to declare their preferred candidate.

 

House of Representatives Speaker Nancy Pelosi, Senate Majority Leader Harry Reid and Democratic National Committee chairman Howard Dean were to release a statement Wednesday urging the party to close ranks against McCain, the Huffington Post website and CNN reported.

 

"The move ... is an indication that few figures beyond Clinton's utmost loyalists are willing to stomach a prolonged vacation period for the New York Democrat to make up her mind," the Huffington Post said.

 

Obama, who must now mend his divided party, paid lavish tribute to Clinton as "a leader who inspires millions of Americans with her strength."

 

"Our party and our country are better off because of her, and I am a better candidate for having had the honor to compete with Hillary Rodham Clinton."

 

Obama captured the final primary in Montana, after a flood of endorsements from Democratic superdelegates during the day, and vaulted over the winning post of 2,118 delegates needed at the party's August nominating convention.

 

According to RealClearPolitics.com, Obama now has 2,165 delegates to the former first lady's 1,923.

 

Clinton snapped up a consolation victory in South Dakota's primary, taking 55 percent of votes to Obama's 45 percent. In Montana, Obama had 56 percent to Clinton's 41 percent.

 

Obama turned his full fire on McCain, saying: "It is not change when John McCain decided to stand with (President) George Bush 95 percent of the time, as he did in the Senate last year."

 

McCain got his attack in first, branding Obama the "wrong change" for America, in a speech also distancing himself from the unpopular Bush.