Utah and North Carolina will duke out their desire for an additional U.S. House seat Wednesday before the Supreme Court, which will decide which state has properly interpreted the U.S. Constitution's meaning of an "actual enumeration" of state populations.

The Constitution demands an "actual enumeration" every 10 years. States can gain or lose congressional seats based on shifting populations.

Utah contends the U.S. Census Bureau is using a process called "hot-deck imputation" as a means of sampling, which the high court has already struck down.  North Carolina and the Commerce Department, which is defending the process, argue that sampling and imputation are not the same.

"This is a method the Census Bureau used with the full knowledge of Congress for the past 40 years to resolve inconsistencies and incomplete data at the end of the process," said William Dellinger, the lawyer for North Carolina and former U.S. solicitor general.

Utah Gov. Mike Leavitt disagrees.

"It's simply an issue of fairness. We want the seat," Leavitt said.

Under the 2000 Census count, Utah — which unsuccessfully claimed that thousands of Mormon missionaries abroad should be included in the count — ended up with 856 less people that North Carolina based on the imputed figures.

The method allows census enumerators, who have had no luck finding occupants at presumed households after six personal visits, to assign the same number of occupants to that home as are living in the nearest neighbor's.

When the Census Bureau did that, North Carolina, which had four times as many imputed households, edged out Utah for the final congressional seat.

Utah would win the seat if the Supreme Court agrees that there's no way to tell whether the "phantom" households are businesses, storage units, or not legitimate addresses at all.

"If there were six follow-up visits and you still don't know whether it's occupied, the best conclusion is it's not occupied," said Tom Lee, a Brigham Young University law professor who will argue Utah's case before the Supreme Court.

"These are not phantom households," said Dellinger

The Census Bureau says it has studies confirming that 75 percent of "imputed" households are occupied homes, but Lee said the bureau made broad assumptions about many addresses in the 2000 master address file without evidence to back them up.

The Supreme Court will issue its ruling before the fall elections, leaving Utah waiting on whether it will have a fourth congressional district. If the Supreme Court orders the Commerce Department to reapportion the states, North Carolina candidates will have to drop their campaigns for the new 13th congressional district.

"North Carolina believes it won this seat fair and square. It's just too late for Utah to be challenging the results of the census," North Carolina Attorney General Roy Cooper said. "It would cause serious problems to undo" the results of the 2000 census, he added.

From the start in 1790, the census never was an actual head count. Surveyors — federal marshals at first — sometimes asked heads of household to provide numbers or relied on neighbors or postmasters. Beginning in 1970 the Census Bureau asked households to fill out and return their own forms by mail.

The Associated Press contributed to this report.