(Reuters) STURGIS, S.D. - Republican presidential candidate John McCain attempted to harness a powerful engine of heartland conservatism on Monday - addressing a giant rally of motorcycle enthusiasts.

Hundreds of thousands of people converge on the remote town of Sturgis, South Dakota, each year for a week-long festival of rock music, wild, good times and American biker culture.

"I recognize that sound," McCain said as dozens of bikers revved their engines as he walked on stage in a sustained growl of approval. "It's the sound of freedom."

The U.S. economy, energy and foreign policy are key issues in the contest between McCain and rival Barack Obama but the race could turn on competing visions of U.S. values.

With their love of the open road, many bikers see themselves as standard-bearers of American freedom.

An endless procession of bikers, many not wearing helmets, cruised the rural roads around Sturgis on Monday in a blur of chrome and leather.

The bikers form a natural audience for McCain. Many are war veterans who say they see McCain as an embodiment of patriotism and service because he spent years in a North Vietnamese prison during the Vietnam war.

Seven bikers carrying big U.S. flags escorted McCain's Straight Talk Express bus into the Buffalo Chip fields where the festival was held.

But Kip Benbow, who rode his Harley three days from Indiana for the convention, said he supported McCain because he would defend another aspect of his way of life.

"I want the right to protect my house and my property. That's my freedom and my right to arms. I don't want nobody messing with my guns," said Benbow, who said he had as many as 40 guns at home.

McCain made his pitch to the bikers not on gun rights but on the issue he said was at the core of freedom: honoring the military.

"You are the heartland of America," he told a crowd of thousands after a searing rendition of the U.S. national anthem played on electric guitar. "You are the heart and soul of America and I am honored to be in your company.

The bikers revved their engines in a deafening roar of approval.

This video is from CNN.com, broadcast August 5, 2008.

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