by John McCormick, updated

DES MOINES – Sen. Barack Obama just gave a fired-up appearance during a warm-up show, before he led a march of several thousand supporters into the Jefferson Jackson dinner.

"I've been instructed not to give a long speech," said Obama, wearing a white shirt with his sleeves rolled up. "I've got to save my delicate voice for the JJ dinner, plus I don't want to use up all my good lines."

Obama is also using his "Fired Up, Ready to Go" campaign trail chant this evening.

"Are ya fired up? Are ya ready to go?" he asked the crowd. "I am excited...First of all, I'm excited because I haven't seen my wife in a couple of days. Seeing Michelle always gets me excited."

The Illinois Democrat previewed some of the themes he will use later this evening, including the American dream and how individuals can make a difference.

"Your voice can change the world. Your voice can change health care. Your voice can change education. Your voice can change America," he said.

Before Obama's appearance, Tommy Vietor, his Iowa press secretary, told reporters the campaign expected 3,000 of their supporters to attend the event. If true, that would represent about a third of the total expected audience.

"We see JJ as a show of organizational muscle as well as a time to deliver a message," Vietor said.

Vietor said the campaign placed 11,000 signs around the arena and had supporters from all of Iowa's 99 counties.

Michelle Obama introduced her husband, after a warm-up concert by R&B singer-songwriter John Legend. She described her husband as someone who is "cute," "tall," "skinny," and who has ears that "stick out."

She also pitched some other important qualities: "He's decent. He's honest and he tells the truth."