After falling behind Atlanta last year for both total flights and passengers, Chicago regains the distinction of having the world's busiest airport--at least for flights--in the first six months of this year.

O'Hare International Airport recorded 477,001 takeoffs and landings through June, putting it slightly ahead of Atlanta's Hartsfield-Jackson, even though both airports saw modest declines from a year ago, according to Federal Aviation Administration data released Monday.

The declines came amid an increasingly competitive environment where airlines are reducing the frequency of flights to fill more seats as they seek to reduce fuel and labor costs. Atlanta-based Delta Air Lines also is focusing more on international flights as it works to restructure after its bankruptcy filing last fall.

Through the first six months of this year, O'Hare saw a 1.3 percent decline in flight traffic from a year earlier, and Hartsfield-Jackson was down 5 percent, to 472,431, the FAA reported. Traffic at the nation's No. 3 airfield, Dallas-Ft. Worth, fell 2.1 percent to 348,434.

"Given the strength of the O'Hare market, it is no surprise that O'Hare is back on top," said Chicago Department of Aviation spokeswoman Wendy Abrams. "The city is committed to maintaining Chicago's role as the preeminent aviation market. We look forward to adding much-needed capacity to keep pace with expected demand."

Chicago's Midway Airport, where Southwest Airlines has a large presence, saw traffic increase 3.1 percent, recording 145,377 flights and ranking 28th nationally. Passenger volume at the Southwest Side airport through May was 7.3 million, up 13.5 percent from a year ago.