The fight for top-billing in Saturday’s Nevada Democratic presidential caucus has become much like its model in Iowa: an hour-by-hour test of who has the best organization.

But unlike Iowa, Nevada never really has done this before, and not on the scale an early caucus date requires. No one knows for sure what the best organization should look like in a state with two major population centers and vast stretches of desert in between.

As the top three candidates made their final pitches to voters, their organizations geared up to find out.

This presidential campaign is the first time the state’s caucus has attracted such attention and effort, and the first time it’s been scheduled early enough to play a role in who becomes the party’s nominee.

The prized position on the nominating calendar was an odd pick, organizers here soon learned.

With a transient population, a libertarian history and a work force with odd hours, Nevada is not a state prone to political enthusiasm. Just 9,000 Democrats caucused in 2004. Estimates for Saturday’s turnout range from 30,000 to 100,000.

Presidential campaigns have been plotting for nearly a year on how best to drive vast numbers of Nevadans to the more than 500 caucus sites statewide by 11:30 a.m. PST Saturday. They’ve been testing volunteers to see who delivers on promises to show up at house parties or phone banks. They’ve worked to lower what one campaign worker called a surprising “50 percent flake rate” — the percentage of no-shows at events.

Hillary Rodham Clinton and Barack Obama appear best positioned to pull off the organizational feat. Both have had more than 100 staff, including dozens of field organizers, on the ground for weeks. Both transferred additional workers from Iowa and New Hampshire as reinforcements.

Obama brought in the head of his winning Iowa team to lead the effort. He also secured a clutch endorsement from the state’s most powerful and disciplined union, the 60,000 member Culinary Workers Union, Local 226, which has a history of influencing the outcome in November.

Clinton’s campaign is powered by party activists, prominent endorsements and unions of her own. The American Federation of State, County and Municipal Employees represents just 3,000 members in Nevada, but the union has imported 125 paid political workers to the state.

John Edwards’ manpower has lagged, but he has parlayed support from steelworker and carpenters unions into a solid base with a crop of seasoned organizers working the streets. His campaign says it received 75 new staff after the Iowa and New Hampshire contests, nearly tripling its total.

A recent poll showed any one of the three could land in front.

So the morning of the caucus will begin for Obama’s campaign in the dark, state director David Cohen said. While Iowa’s evening caucus gave workers all day to remind and corral supporters, Nevada’s morning caucus means field workers will be trying to catch people at first light.

“For the field guys it’s going to be a long night,” Cohen said.

The Obama campaign’s “van plan” has reserved more than 50 vehicles to give rides to those who call into a hot line.

Edwards precinct captains will start the day picking up information packets at one of three offices and about dozen “staging areas.” The packets give instructions on the complicated mathematical formula used to assign delegates. (Obama’s campaign is handing out calculators.) It also includes key campaign talking points for precinct captains to try to persuade other caucus-goers to join their ranks.

“We believe the last 24 hours is primarily about making sure all your precinct captains have the material they need, making sure everyone knows where to go and what to say about John Edwards,” said Edwards campaign spokesman Adam Bozzi.

The Clinton campaign’s information packet is a “tote bag with some T-shirts and goodies,” said her Nevada campaign director Robby Mook, who a sent U-Haul truck full of them to Reno late Wednesday.

Mook said the campaign has a “senior transportation program” to accommodate its large number of elderly supporters. Many are clustered in retirement communities and will hitch rides together, he said. More than 100 vehicles are reserved to provide transportation.

The Clinton camp also ensured that most of its drivers speak Spanish, a plus with Nevada’s large Hispanic population.