Chicago ? There hasn’t been a competition between Chicago and Atlanta this fierce since the Cubs beat the Braves in the baseball playoffs. Chicago is claiming victory again in having the world’s busiest airport, but Atlanta is saying, “Not so fast.”

The perennial rivalry between the airports is a game of definitions and numbers on which even the experts don’t agree.

Chicago’s O’Hare International Airport had the most takeoffs and landings in 2003 — 928,735 according to the National Air Traffic Controllers Assn., or 931,000 according to the Federal Aviation Administration.

But Hartsfield-Jackson Atlanta International Airport is projected to have the most passengers with 58,875,694 through September, the latest numbers available.

“We don’t have a World Series of airports,” said Hartsfield-Jackson spokesman Robert Kennedy.

O’Hare spokeswoman Monique Bond downplayed the rivalry, but insisted O’Hare is the world’s busiest.

“It’s one of those lighthearted competitions, so to speak, that people always look to at the end of the year,” Bond said.

FAA spokesman William Shumann said takeoffs and landings as well as passengers are both valid measures for determining which airport is the world’s busiest. That, he said, can make the annual title elusive. But such a title has a downside, Shumann said.

“As a passenger you might get through the airport with no trouble because there aren’t a lot of people and the plane pushes back on time, but unfortunately there are 10 planes waiting to take off in front of you,” he said.