NEW ORLEANS – The mayoral race here, which got its official start last week, is presenting candidates with a daunting question of post flood strategy: Who and where are the voters?

Although about half of New Orleans’ residents have returned since Hurricane Katrina, tens of thousands of evacuees are still scattered across the country and eligible to cast ballots in the April 22 election, either by mail or at satellite polling places around the state.

But even more challenging in a city where racial allegiances – real or imagined – can determine political fates, is the question of who those voters will be.

Once dominated by a significant black majority, the city’s demographics have shifted toward whites, and the new, uncertain racial balance has given the contest a particularly unpredictable feel.

With credible white challengers to incumbent C. Ray Nagin, Democrat, among a field of 24 candidates, and the looming possibility that the election will yield the first white mayor since 1978, even basic logistical questions regarding election dates and how to notify displaced voters have become bogged down with lawsuits and racial overtones.

“There is a strong sense in the black community that some in the white community are trying to pile it on,” City Council President Oliver Thomas Jr. said last week. He predicted that anger will motivate many displaced voters to cast ballots, even if it means taking long bus trips back.

Meanwhile, the electorate’s new geography is transforming the mayor’s contest into a far-flung affair. Candidates are planning campaign stops and possibly even advertising in places as far away as Atlanta, Houston, Dallas, Memphis, and Jackson, Miss.

Mr. Nagin campaigned in Houston over the weekend, and supporters in Memphis were already arranging buses to send voters to New Orleans for the election next month, he said.

Lieutenant Governor Mitch Landrieu and Ron Forman, chief executive of the Audubon Nature Institute, considered the two leading challengers to Mr. Nagin in a field of more than a dozen so far, likewise say they will divide their time between New Orleans and other cities where New Orleanians can be found. Mr. Nagin’s leadership in the months after the hurricane is expected to be a key issue in the campaign.

Some analysts expect the best-funded campaigns will even run television ads in markets such as Houston, Atlanta, and Baton Rouge, La.

“It’s peculiar,” Mr. Landrieu said of the diaspora of New Orleanians. “It’s twisted a lot of people’s heads. We’re just going to have to figure out where we think we know the voters are.”

“It’s a nationwide campaign,” Mr. Nagin said last week after filing papers.

But as formidable as the logistical challenges may be, it is the new racial balance in the city created by Hurricane Katrina that has lent the mayoral contest a volatile character.

The racial fears and anger now coalescing around the election began to stir as far back as the flooding that left thousands of poor, black New Orleanians stranded for days inside the Louisiana Superdome – and then got worse as authorities began to speak of New Orleans with a diminished black population.

In the weeks after the storm, Jimmy Reiss, a wealthy New Orleans businessman, angered many blacks with a comment in the Wall Street Journal: “Those who want to see this city rebuilt want to see it done in a completely different way: demographically, geographically, and politically.”

Then Secretary Alphonso Jackson of the Department of Housing and Urban Development, in a visit to Houston, told the Houston Chronicle that “New Orleans is not going to be as black as it was for a long time, if ever again.”

Some black leaders, such as Stephen Bradberry, a neighborhood organizer with ACORN in New Orleans, still refer to those remarks. ACORN (a community organization of low- and moderate-income families) and another group sued in federal court to compel the state to open out-of-state polling places for Katrina evacuees, most of whom are black. The court ruled against the idea.

Now those potential voters must travel long distances or perform a two-step mail-in process: They must first write to request a ballot and then send it in.

“It’s almost so obvious that there’s a concerted plan to make this a whiter city,” Mr. Bradberry said. “You don’t want to believe it because it would be too disturbing.”

The mayoral election, originally scheduled for February 4, had to be postponed because of hurricane damage. Then even the date chosen for the new election – April 22 – became, for some black leaders, a racial issue.

Some business and political leaders urged that the election be held as early as possible to keep the incumbents’ terms from being extended without voter approval. But Mr. Bradberry and other activists said it should be delayed to give evacuees, many of them black, more time to move back to the city.