Sarah Palin, former governor of Alaska, adjusts her helmet before taking part in the Rolling Thunder motorcycle ride to honour US veterans in Washington May 29, 2011. [Photo/Agencies]

WASHINGTON - US Republican Sarah Palin rolled into Washington on the back of a Harley-Davidson on Sunday, sparking a frenzy of attention and renewed speculation about her 2012 presidential plans.

Dressed in black jeans, leather jacket and helmet, Palin opened a campaign-style East Coast bus tour by joining tens of thousands of participants in the annual Rolling Thunder motorcycle rally to honor military veterans.

Her arrival in a Pentagon parking lot where the riders gathered set off a crush of photographers and cheering fans seeking autographs, many urging her to run for the White House and shouting "Sarah, we love you."

"Thanks for doing what you're doing for the veterans," the 2008 vice presidential nominee told one rider as she chatted with fans, posed for photos and signed T-shirts and posters.

Palin's bus tour and other recent moves have generated a burst of speculation about whether she will enter a slow-starting Republican race for the right to challenge President Barack Obama in 2012.

Many Republicans are unhappy with the field and have urged others to enter. Palin would be the best-known candidate in a race that includes former Governors Tim Pawlenty of Minnesota and Mitt Romney of Massachusetts along with former House of Representatives Speaker Newt Gingrich.

Palin's political action committee says the bus tour of historical sites on the East Coast is part of an effort to educate Americans on the country's founding principles, although it has been vague about the details.

But her participation in the motorcycle rally spotlighted her undeniable star power. Her appearance, along with husband Todd and daughters Bristol and Piper, thrilled fans and drew grumbles from riders who said she was politicizing the rally for military veterans that takes place each year during Memorial Day weekend.

"I don't think you should be using this to run for public office, this is to honor vets," said Richard Orndorff, of Winchester, Virginia, who arrived at the Pentagon before dawn to line up for the ride.

'Not the place for politicians'

Sarah Palin, former governor of Alaska, rides on the back of a motorcycle at the start of the Rolling Thunder motorcycle ride to honour US veterans in Washington May 29, 2011. [Photo/Agencies]

"This is definitely not the place for politicians," said Ed Ellis of Middletown, Virginia.

Artie Muller, national executive director of Rolling Thunder, said Palin was welcome to attend the event like any other American. "We're all here for a reason. She's just like anybody else," he said.

Palin was hardly like anyone else at the event, however, cruising into the lot with a police escort 45 minutes before starting time and eventually taking a place near the front of the line, which snaked for miles through the mammoth lot.

She shouted "Whoo!" and gave a thumbs-up and wave as tens of thousands of motorcycle engines revved for the ride across the Potomac River from Virginia to the event near the Vietnam Veterans Memorial on the Mall in Washington.

Palin ignored shouted questions about a presidential run and said "Heck no, I'm an American," when asked if she was politicizing the rally. "I'm out here supporting veterans," she told CNN.

"There's no better way to see D.C. than on the back of a Harley," she said in a statement after the rally, adding she was more used to snow machines than motorcycles but both celebrated "a free spirit."

After meeting Palin, Chris Rogers of Gaithersburg, Maryland, showed off her T-shirt with signatures of the former Alaska governor and husband Todd.

"I thanked her and said to tell her family thanks for all of the obnoxious stuff they have to put up with," she said.

In addition to the bus tour and a revamped website, Palin has authorized a film about herself that will premiere next month in Iowa, the state that kicks off the nomination race in February, and reportedly bought a home in Arizona where she could base her campaign.