Mayor Ray Nagin and Lt. Gov. Mitch Landrieu will compete in a runoff next month following Saturday's mayoral election, a tricky experiment of modern-day democracy that gave voters scattered by Hurricane Katrina a say in this city's future.

With 91 percent of precincts reporting in the nonpartisan primary, Nagin topped all candidates with 38 percent or 28,123 votes but fell short of the majority he would have needed to win a second term and avoid the May 20 runoff.

Landrieu had 29 percent, or 21,154 votes. Nonprofit executive Ron Forman followed with 17 percent, 12,650 votes, and 19 other candidates trailed far behind.

Landrieu cast his showing as a testament to the unity the city needs after Katrina, a storm that he said put all of New Orleans "literally in the same boat."

"Today in this great American city, African-American and white, Hispanic and Vietnamese, almost in equal measure came forward to propel this campaign forward and loudly proclaim that we in New Orleans will be one people. We will speak with one voice and we will have one future," he said, flanked by his father, Moon Landrieu, the last white mayor of New Orleans in the late 1970s.

Elections officials say the voting was steady and unusually problem-free, and while they didn't immediately have complete numbers, the early returns suggested the turnout could be low.

Of the city's 297,000 registered voters, tens of thousands are spread out across the United States. More than 20,000 cast ballots early by mail, fax or at satellite voting stations around the state, and thousands more made their way to 76 improvised polling stations. Some traveled by bus or in car caravans from such evacuee havens as Houston, Dallas and Atlanta.

"Let me tell you something. This is an important election," said Gerald Miller, a 61-year-old stroke patient whose daughter was pushing her in a wheelchair. "We're going to straighten this mess out."

Around the city, a mixture of black and white voters were seen moving steadily in and out of the "super polling places" that stood for the dozens of wrecked schools and churches where residents would ordinarily have voted.

"It means a lot because whoever gets elected is going to help us rebuild," said 57-year-old Lorraine Payton. "This is about trying to save us right now."

The winner of the mayoral and city council races will face a host of politically sticky and racially charged decisions about where and what to rebuild in a city where whole neighborhoods remain uninhabitable.

Four-fifths of the city was flooded, and large parts of New Orleans are still woeful tracts of ruin. Rebuilding plans — and the federal money to pay for them — are being debated. Nearly all the public schools remain closed, and the tourism business, long the economy's mainstay, has drawn few conventions.

Nagin said at a precinct in his neighborhood Saturday that, with another hurricane season just weeks away, this is no time for a transition of administrations. "We don't have a year to wait," he said.

The 49-year-old former cable television executive became known in the immediate aftermath of Katrina for sometimes shaky leadership and frequent off-the-cuff remarks, such as when he cursed the sluggish federal response and later suggested that God wanted New Orleans to remain a "chocolate" city. Nagin stood by the comment and later said he was convinced the black vote was "coalescing" around him.

His chief challengers are white: Landrieu, brother of Sen. Mary Landrieu, and Forman, chief executive of the Audubon Nature Institute, which oversees the city's zoo and aquarium. Forman won the endorsement of business leaders and the city's major newspaper, The Times-Picayune.

Race has become a key factor in the election. Less than half the city's pre-Katrina population of 455,000 have returned, and civil rights activists note that most of those scattered outside the city are black. Prior to the storm, the city was more than two-thirds black; it has not had a white mayor since 1978, when Landrieu's father, Moon Landrieu, left office.

The Rev. Jesse Jackson has said he plans to challenge the election outcome in court regardless of the winner, arguing displaced voters were disenfranchised because they weren't allowed to vote in polling places in such adopted cities as Houston, Dallas and Atlanta.

Of the ballots cast prior to Saturday's election, about two-thirds were cast by black voters, but analysts caution the numbers may not reflect overall turnout. The racial breakdown of the full vote was not immediately released.

Ater said he's confident that election officials, who fielded thousands of calls from voters on where to vote, did what they could to educate voters.

But not all evacuees who returned to New Orleans on Saturday were able to cast ballots. Dana Young, an 18-year-old college freshman who traveled by bus from Atlanta, was told at the polls that there was no record of her registration. Young said she had a voter registration card but lost it along with her birth certificate during the hurricane.

"I'm really upset," she said as tears welled up in her eyes. "I came all the way down here and now I can't do anything about it. They said they couldn't find me in the system, so I can't vote."