Audience reverent, then roaring as Obama speaks

DENVER (Reuters) - As Barack Obama spoke on Thursday night to a packed football stadium in Denver, the audience of some 75,000 people alternated between reverent silence and a roaring approval that shook the stands.

The crowd, many of whom arrived up to six hours before the speech, gave the Democratic nominee for the U.S. presidency a 2-1/2 minute ovation as he took the stage to cap an evening of songs and speeches by politicians, celebrities and ordinary Americans.

Flanked by white columns, American flags and two huge television screens that projected his image to the packed stadium, Obama took 43 minutes to lay out his plan for an America under his leadership.

While the audience was almost completely silent during a video introduction of the first-term Illinois senator unknown to most Americans just a year ago, they came to life with chants of "Yes we can" and "Eight is enough" as Obama called for change after eight years of President George W. Bush's Republican presidency.

"He's really good," breathed Mark Rosa as Obama spoke. The 21-year-old Denver college student arrived four hours before Obama spoke and studied for a physics test in the hours as she waited for one of the most anticipated speeches of recent U.S. election campaigns.

Before Obama took the stage, the crowd sang along to a recording of Bruce Springsteen's "Born in the USA" and basked in an atmosphere that was both relaxed and celebratory.

As he spoke, the crowd first stood in ovation then fell silent as the 47-year-old senator began to speak. Though some had feared the acoustics of the cavernous stadium might hurt Obama's delivery, each word could be clearly heard.

The crowd disappeared behind a sea of small American flags and blue-and-white signs reading "change" each time Obama said something they approved of and when he took on Republican rival John McCain, whose own party convention takes place next week.

While several hundred seats at the top of Invesco Stadium were empty, people stood in the aisles in other sections of the massive arena, and small knots of fans watched the address on television screens in the bowels of the building, deterred by the crush of people in nearby sections.

In addition to the two television screens onstage, three huge screens projected the speech from the tops of the stands, and the stadium lights lit up the blue-carpeted stage. At the end fireworks lit up the night sky.

(Additional reporting by Kevin Drawbaugh and Rob Doherty)