NEW ORLEANS—Nobody really knows how many people live here.

Ever since this city was full of water and nearly empty of residents in September 2005, the true size of New Orleans has been a matter of wild uncertainty. Even today, population estimates can swing by the tens of thousands.

“;There's a range out there that might be as big as 50,000,”; said Ken Hodges, chief demographer for Nielsen Claritas, a market research firm. “;There is still a substantial amount of uncertainty.”;

By early 2011, however, the city's population will finally become an official number, if not a hard fact.

This year's census will be revealing and important in every city, of course, according to the crude math that each citizen equals a certain amount of government money and political clout. But the stakes of the census here, as in other hurricane-battered cities and towns from Moss Point, Miss., to Galveston, Texas, are more profound.

The final numbers, no matter how much people here may challenge them—and challenges are almost a certainty—will go far in determining how New Orleans thinks about itself, whether it is continuing to mount a steady comeback or whether it has sputtered and stalled, how far it has fallen in the ranks of the country's cities, and how quickly it is likely to rise again.

Determining how many people live here will not be an easy task, given the thousands who are still homeless or living with relatives as they await permanent housing, and the bureau is allowing some unconventional counting practices. The results should show who the city's residents are, answering one of the most agonizing questions that has lingered after Katrina: What is the true size of the city's black majority, once as large as two-thirds of the population?

In neighborhoods like Gentilly Woods, it is still difficult to tell by sight exactly which houses are occupied but badly in need of repair and which have been abandoned. The city's excessive housing stock, built for a population that was once more than half a million, obscures the dimensions of the current populace like an oversize coat.

To local officials, the uncertainty about New Orleans' size has been as convenient as it is has been frustrating. Per-capita murder rate too high? No, the population estimate is just too low.

Mayor C. Ray Nagin and other officials have routinely challenged census estimates as too low, and have generally been successful. The Census Bureau's official number has steadily risen with each revision, and today stands at just less than 355,000, or nearly 75 percent of the population of 484,674 in the 2000 census.

These estimates have their critics but are generally seen as the best available portraits of the city until this year's census is complete.

“;I would be surprised if the count came in much differently from what the estimates are,”; said Allison Plyer, the deputy director of the Greater New Orleans Community Data Center, a local nonprofit group. Still, she added, “;don't count your chickens before they're hatched.”;

Others are less confident in the numbers and think a general desire for good news about New Orleans is distorting both the estimates and the census itself. Elliott Stonecipher, a political analyst and demographer from Shreveport, points out that the Census Bureau is allowing departures from traditional head-counting practices, because of the extraordinary circumstances of the Gulf Coast.

This year, for example, the bureau has distributed census forms to people who are not at verified addresses, a practice usually reserved for remote rural areas.

Stonecipher also cites public appeals by local leaders to count those who intend to return to the region as if they were already living here, though federal officials insist that is not how the census is supposed to work.

All of this, Stonecipher said, could lead to an overcount, or at least an unreliable tally.

“;Everyone desperately needs a real and fair count of New Orleans,”; he said, “;and we're not going to get it.”;

But even the rosiest result could come as a jolt. New Orleans will officially be much smaller than it was in 2000, at best barely making the list of the 50 largest cities in the country. Much of the federal money apportioned to the city will reflect that for the next decade, asrecovery dollars dwindle and the Katrina evacuees continue to trickle back, prompting calls by Nagin, who leaves office next month, and officials in neighboring parishes for a special census in 2011 or 2012.

“;Whatever our population is, we are still acting like a 450,000-person city,”; said James Perry, director of the Greater New Orleans Fair Housing Action Center, a private, nonprofit civil rights group. “;The money is going to take us out of denial pretty quickly.”;

The city could see a drain of its political power as well. The Louisiana Legislature faces what promises to be a thorny redistricting session in 2011, and New Orleans is all but guaranteed to lose seats in the Statehouse.

The potential political shift is tied up in what could be the most charged finding of the census: the true size of the city's black majority. Some say the size of that majority could turn out to be lower than it appears in current estimates, which have it at roughly 62 percent.

“;I think it's going to be a big shock,”; said Trupania Bonner, the executive director of Moving Forward Gulf Coast, a nonprofit organization founded after Katrina to aid the rebuilding effort.

The people who have faced the toughest obstacles to returning, like low-income renters and the elderly poor, are most likely to be black, Bonner said. They are trying to return from places like Houston or Atlanta, but without some of the advantages given to those who owned homes before the storm. “;We are penalizing folks who have to rebuild at their own pace,”; he said.

As of Wednesday, the rate at which census forms were being returned from New Orleans stood at around 39 percent, far below the national average of 63 percent. Bonner, who has been holding community meetings about the census throughout the region, said that many poor people felt that the federal government had continually let them down over the past five years, and they have a hard time understanding why they should participate now in a federal census.

But even if the response rate jumps, Bonner said he was not optimistic about a high final count, at least not here.

“;We're going to watch Texas gain four seats and Georgia gain two,”; he speculated, referring to congressional districts. “;Those are our folks, man.”;