Aug. 28 (Bloomberg) -- When Barack Obama strides onto the 50-yard line of Denver's mile-high Invesco Field tonight to accept his party's nomination, expectations will be just as elevated.

After all, it was in part his keynote address to the Democratic National Convention in 2004 that got him here. In this campaign, he has delivered more than 1,000 speeches, and the quality of his oratory has helped catapult him from an unknown Illinois state senator to the head of his party in less than four years.

His decision to move his prime-time acceptance speech to a 76,000-person football stadium carries no small risk, and Republicans pounced on aerial photos of a colonnaded stage reminiscent of the White House portico or a Greek temple, fodder for their depiction of Obama, 47, as an arrogant celebrity. Obama's challenge is to engage his listeners, rather than dazzle them -- and to sidestep criticism that he is all flash.

``The setting raises the stakes that much more; it's like a high jumper saying, `Raise the bar a couple more inches, this isn't challenging enough,''' said Robert Schlesinger, author of ``White House Ghosts: Presidents and Their Speechwriters.''

``It's brilliant if he clears the bar, but it's not good if he knocks it down,'' Schlesinger said.

Solutions, Inspiration

Obama's test, strategists and speechwriters said, is to present his unusual, multicultural biography in a way that ordinary Americans can relate to -- and that conveys a grand and pragmatic vision for the nation. With polls showing that more than 80 percent of voters consider the country to be on the wrong track, he will need to offer solutions as well as inspiration.

``He wants to be able to define his priorities, convey optimism and hope, and draw contrasts'' with Republican candidate John McCain, said Democratic pollster Peter Hart. ``But it's not a State of the Union; it's a political speech and those are about vision. If he gets into a laundry list of issues, it's a loser.''

Curt Smith, a former speechwriter for President George H.W. Bush, said telling a compelling and accessible life story is crucial to cementing voters' understanding of a candidate and his values.

`Embodiment'

``When you become the embodiment of the people whom you want to vote for you, that's every politician's dream,'' Smith said.

Obama ``should sketch his personal narrative and make it emblematic of the silent majority,'' said Smith, citing President Richard Nixon's 1968 speech, in which the Republican described himself as a onetime poor young boy listening to train whistles, dreaming of impossible journeys, who now stood before his nation, ready to serve as its leader.

Obama isn't the first candidate to accept the nomination at a huge outdoor venue. In 1960, John F. Kennedy described a ``New Frontier'' at Memorial Coliseum in Los Angeles before more than 50,000 people, and Franklin D. Roosevelt urged 100,000 listeners to seize their generation's ``rendezvous with destiny'' at his 1936 speech at Franklin Field in Philadelphia.

Obama is comfortable with crowds; he addressed 200,000 people in Berlin in July and 75,000 in Portland, Oregon, in May.

`Rock Concert'

Still, he must ensure that tonight's event doesn't turn into ``a rock concert that will play right into Republican plans,'' Smith said. ``Somehow, he has to be intimate in an 80,000-seat football stadium.''

The author of two best-selling books, Obama took the lead in writing his address, and holed up for several nights in a Chicago hotel room last week rereading his favorite acceptance speeches, scribbling on a pad and editing drafts with his head speechwriter, Jon Favreau, and strategists David Axelrod and Robert Gibbs.

Obama's chief inspirations for his acceptance speech were the one Kennedy gave in 1960, Ronald Reagan's in 1980 and Bill Clinton's in 1992, Axelrod said.

Political speechwriters said determining how much time to spend on biography, vision and plans requires a delicate balancing act.

``His biography should lead naturally to the positions he's taken and the kind of president he's going to be,'' said Jeff Shesol, a former speechwriter for President Clinton.

`New Frontier'

Ted Sorensen, the Kennedy aide who helped craft the ``New Frontier'' address, said Obama should reach out to those who voted for his Democratic rival, New York Senator Hillary Clinton, 60, to ``assure a reunified party after a long and inevitably divisive struggle for the nomination.''

And just as Kennedy had to reassure voters who were uncomfortable with his Catholic faith, Obama still needs to dispel false reports that he is a foreign-born Muslim, and suggestions that his patriotism is questionable.

``His speech at least in part should be autobiographical,'' Sorensen said.

Michael Waldman, principal author of Clinton's 1996 acceptance speech, said widespread discontent with the state of the nation means Obama ``shouldn't spend most of the speech talking about his story; he should talk about our story.''

`Man From Hope'

Similarly, Reagan's address reached out to those who became known as Reagan Democrats. Clinton's 1992 ``Man from Hope'' speech rebranded Democrats as centrists and the party of the middle class.

Clinton's first acceptance address is perhaps best remembered for a video introducing the Arkansas governor -- whom Republicans had tried to cast as an Ivy League elitist -- as a humble American, with an up-by-his-bootstraps success story.

The video that will introduce Obama was made by Oscar award-winning documentary filmmaker Davis Guggenheim, director of ``An Inconvenient Truth,'' which chronicled Vice President Al Gore's campaign against climate change.

In 1948, Democrat Harry Truman injected energy into a moribund party when he gave an impassioned acceptance speech well after midnight calling Congress back into session, Schlesinger said. Republican Gerald Ford broke news in his speech by challenging Democrat Jimmy Carter to live debates.

Missteps

There also have been missteps. In 1972, Democratic candidate George McGovern lost an opportunity by speaking after the prime-time audience had gone to bed. Republican George H.W. Bush's famous vow -- ``Read my lips, no new taxes'' -- came back to haunt him.

Obama said this week that he is ``not aiming for a lot of high rhetoric'' tonight. ``I'm much more concerned with communicating how I intend to help middle-class families live their lives,'' he said.

``I want people to come away saying, `Whether I'm voting for the guy or against the guy, I know what he stands for, I know where he comes from, I know what he believes,''' Obama said Aug. 25.

Speaking 45 years to the day after Martin Luther King Jr. delivered his ``I Have a Dream'' speech, the first-term U.S. senator from Illinois is likely to touch on the improbability of a black man having a shot at the country's most powerful office four decades after blacks were barred from sharing bus seats and lunch counters with whites.

Without King's speech and the civil-rights movement of which it was a part, without ``the work and the toil, and the risks that were taken by previous generations, then I wouldn't be in Denver on Thursday accepting the nomination for the presidency,'' he said.

Obama's speech will reflect that historic legacy, said campaign strategist Gibbs, dismissing the suggestion that the huge venue may reinforce the Republicans' caricature of Obama as a shallow rock star.

``My only regret is that the stadium isn't bigger,'' Gibbs said.

To contact the reporter on this story: Indira Lakshmanan at in Denver, or ilakshmanan@bloomberg.net

Last Updated: August 28, 2008 00:39 EDT