Des Moines, Iowa ? On Sunday, Mitch Stewart was a happy man.

In a back room of the Barack Obama for President headquarters here, he was pawing through a mountain of blue, white and green cards that were left with campaign volunteers Saturday by the throngs of spectators who turned out to see Oprah Winfrey endorse the Illinois senator’s campaign for the Democratic presidential nomination.

On Saturday afternoon and evening, at rallies in Des Moines and Cedar Rapids, the media stands were jammed with TV cameras from around the world, recording the first-ever foray into politics by the reigning queen of daytime television and an icon of influence.

Now, 24 hours later, no cameras were allowed back at headquarters, where the real dividends of the extravaganza were being counted.

In the battle for the Jan. 3 Iowa caucuses, no prize is more valuable than live names and numbers. Stewart had come to Des Moines last January, from his previous job as manager of the Democrats’ coordinated campaign in Minnesota, as Obama’s newly hired caucus director. In 2004, he had worked for John Edwards.

During the last 11 months, he has supervised the opening of 38 local offices, each with a quota of caucus-goers to collect. He has dispatched Obama and his wife, Michelle, to hundreds of small-town coffees and town meetings, taking names at every gathering.

The weighting of caucus votes – like that of the Electoral College – favors small towns and rural communities, so it makes sense for the campaigns to reach into these areas.

But 60 percent of the Iowa vote is cast within the reach of Des Moines and Cedar Rapids TV, and in those markets, nothing was bigger last week than the Oprah-Obama show.

It dominated the airwaves and the local press for three days. The day of the Des Moines rally, the Register – the state’s largest paper – had a Page One story about the event that continued for a full page inside.

No admission was charged, but people were asked to apply for tickets online or come by headquarters to get them – facilitating the collection of addresses, phone numbers and e-mails. Those who showed up at the hall were given tickets, too, and asked to fill out the information.

Standing in the lobby of Hy-Vee Hall an hour before the scheduled start of Saturday’s rally, you saw a steady cascade of people coming off the skywalks that connect the downtown stores, and streaming down the escalators into the auditorium.

It was a human metaphor for a political tsunami – men and women, young and old, many families with children, bundled to their chins against the outdoor cold, but patiently waiting their turn to be admitted to what was, in essence, another political rally.

There were no chairs, so those who came early stood for more than hour, listening to band music, before Michelle Obama introduced Oprah, who in turn brought on Obama. A trickle of people left as soon as the introductions were complete, but thousands stayed and listened to an hour of political rhetoric.

Mitch Stewart told me he barely noticed what happened inside the hall. “As long as it wasn’t a disaster, I didn’t care,” he said. “I got 20,000 live names at least, with current phones and addresses” from the 18,500 who came through the doors here and an additional 10,000 in Cedar Rapids. “The phoning will start tonight.”

In all the history of the Iowa caucuses, no one had ever seen an event of this size. The other campaigns could only be envious. And those who turned out for Oprah and Obama can expect to be importuned, in person, by e-mail and by phone, to come to the caucuses. Most probably won’t, but some percentage of them will. Where progress is measured in signing up increments of a dozen or fewer people in a precinct, having a universe of 28,500 to draw from is an awesome advantage.

And having Oprah declare, in full operatic fervor, “I’m here to tell you, Iowa, he is the one. Barack Obama!” – that’s not bad either.