In the 2000 presidential race, Florida made the difference. In 2004, it was Ohio. This year could it all come down to just a single city, Omaha, Neb., and its suburbs?

That’s a scenario being spun out by an amateur political prognosticator from New York, Sheldon Adler, who has a strong record of identifying the ultimate battlegrounds in national elections.

“It’s possible. I don’t think that’s crazy,” Mr. Adler said of the prospect that Nebraska’s 2nd Congressional District, which includes Omaha and its environs, could become a tiebreaker in the November vote.

The possibility of such a decisive role for the Midwestern city exists because Nebraska allocates electoral votes by congressional district rather than on a statewide, winner-take-all basis. Maine is the only other state to use a district-by-district system.

Mr. Adler’s Omaha scenario involves the likely Democratic nominee, Senator Obama of Illinois, taking every state Senator Kerry of Massachusetts won in 2004 with the exception of New Hampshire. Under this carefully chosen sequence of events, the presumptive Republican nominee, Senator McCain of Arizona, hangs on to all of President Bush’s winning states from 2004, except for Iowa, Colorado and either New Mexico or Nevada. The result: a 269-269 tie, with 270 votes needed to win the presidency.

“It really may come down to, in that theoretical case, that one electoral vote,” Mr. Adler said. With Maine expected to go entirely for the Democrats, the potential boon for Mr. Obama and the danger for the presumptive Republican nominee, Senator McCain, is that Omaha might turn blue.

Nebraska, which President Bush carried 66% to 33% in 2004, is considered one of the most reliably red states, so much so that it was the last state in the union to get a visit from the peripatetic President Clinton, who finally touched down there two months before leaving office.

Of the five electoral votes up for grabs in the Cornhusker State, the one belonging to the 2nd Congressional District is considered the best prospect for Mr. Obama, though the area is still not particularly welcoming. By registration, the district is about 44% Republican and 37% Democrat, with 19% independent.

A professor of political science at the University of Nebraska-Lincoln, John Hibbing, cautioned that those numbers understate the district’s conservative bent. “A lot of those Democrats are working-class Democrats who are fairly conservative,” he said.

Mr. Hibbing said the possibility that Omaha could be “in play” in the fall campaign was raised in local newspaper articles soon after Mr. Obama surprised many observers by drawing a capacity crowd of more than 10,000 people for a rally in the city in February. “There was a lot of enthusiasm around Obama in Omaha,” the professor said.

A poll taken in February by SurveyUSA showed Mr. Obama with a narrow lead over Mr. McCain in both the Omaha district and another that covers the rest of eastern Nebraska. However, Mr. Hibbing said he sensed that support for the senator from Illinois has ebbed. “My prediction would be that McCain will win, especially with the luster going off the Obama thing,” he said.

Mr. Hibbing noted that Nebraska has never split its electoral votes since it decided in 1991 to adopt the unusual system of allocating one vote to each district and two to the statewide winner, but he said it was possible Mr. Obama could upset that tradition. “It’s not beyond the pale. It’s something worth thinking about,” the professor said.

While Omaha has never been considered a bellwether, it has long been one of the top test markets for retailers and restaurant chains. If Omahans are willing to buy what Mr. Obama is selling, perhaps the rest of American will, too. The second district is also home to a billionaire investor considered the world’s wealthiest man, Warren Buffett. He has raised funds for Mr. Obama and Senator Clinton and is expected to back the Democratic nominee.

Mr. Adler, a corporate lawyer for Skadden, Arps in his day job, is careful to warn that he is not predicting the Omaha scenario as the most likely outcome in November. “It’s more likely to tip one way or the other,” he said. Still, he notes that more prominent pundits such as NBC’s Tim Russert have been talking about a possible electoral vote split in Nebraska.

In 2000, Mr. Adler gained notice in New York circles for an e-mail he sent a week before the election predicting that the election would turn on Florida. He had a near-perfect record in 2004 but blew the overall result by giving Ohio to Mr. Kerry rather than Mr. Bush.

Mr. Adler, who said he usually supports Democrats but is pleased that Mr. McCain is the likely Republican nominee, has not yet tackled the Omaha scenario in the political newsletter he now distributes to about 200 friends. Coming editions may have to cover other razor-close possibilities long pondered and salivated over by political junkies. These include the deadlock produced by a flat-out tie, as well as a president chosen by a so-called faithless elector who switches sides when the electoral votes are cast.