DES MOINES, Iowa - Even before Oprah Winfrey adopts her familiar pose - microphone in hand - in the unfamiliar venue of the presidential campaign, Barack Obama is already reaping the benefits of her high-wattage celebrity backing.

Thousands of Iowans have flocked to his office, and 1,385 have signed up as volunteers to score tickets to see the talk show diva. The campaign declines to say how many tickets have been distributed for two events today in Iowa but says no one will be turned away from the opportunity to attract new voters.

After all, Obama is engaged in a tight, three-way race with Hillary Rodham Clinton and John Edwards and the Jan. 3 caucuses are less than four weeks away.

Obama entered the Democratic presidential race with a significant disadvantage, a newcomer in national politics running against New York Sen. Clinton and former vice presidential contender Edwards. Winfrey gives Obama female star power to help draw voters. The campaign hopes the "O factor" can sell the candidate the way it does books or products featured on her show.

Winfrey has never backed a political candidate, but on behalf of her Chicago hometown senator, she's making the stops in Des Moines and Cedar Rapids today before heading tomorrow to South Carolina and New Hampshire with Obama and his wife. The campaign moved the biggest event to the 80,000-seat University of South Carolina football stadium after running out of the 18,000 tickets originally available.

Obama adviser Steve Hildebrand in Iowa said two-thirds of those who snapped up the first batch of tickets were voters who had previously been unknown by the campaign. "We'll use this as an opportunity to begin a dialogue with them," he said. Emily Smith, a precinct captain on the west side of Des Moines, has 50 tickets to give out to volunteers. She's working the phones, and to those open to supporting Obama but not yet sold, Smith offers Oprah tickets.

"I work full time so I don't watch her that much, but I've been really surprised how much people love her," Smith said. "I don't think Oprah is going to change anybody's mind necessarily, but it helps me to get people to go see the senator. And I think if they do that, they're going to support him."