WASHINGTON -- A new federal study that for the first time examines the capacity of the nation's busiest airports and the reasons behind the record delays concludes that O'Hare International Airport is overextended and the situation will only grow worse during the next decade.

The report, to be released Wednesday on Capitol Hill, says that even in good weather, the airport operates above capacity for 3½ hours a day, but when weather conditions deteriorate, traffic exceeds capacity for 8 hours.

And despite assurances from Chicago officials that O'Hare doesn't require new runways to handle air travel demands during the next 10 years, the Federal Aviation Administration analysis concludes the situation will only deteriorate as the number of flights grows.

The agency estimates operations will increase by almost 20 percent but that with technological improvements, O'Hare at best can only accommodate a third of the increase.

The findings are contained in an unprecedented study of runway capacity at the nation's 31 busiest airports. The long-awaited data set the stage for a showdown between government regulators, the airline industry and their customers over how to address an airline delay crisis that resulted in one of every four commercial flights in the country arriving late last year.

The FAA report, obtained by the Tribune, puts a particular focus on the key role of O'Hare in creating many of the bottlenecks, noting that O'Hare had the third-highest rate of delayed flights in 2000 and ranked No. 1 in the U.S. in total delays.

The study also casts doubts about the Daley administration's contention that O'Hare has adequate capacity to cope with the projected growth and that there is no need to consider building new runways until at least 2012.

Passenger demand at O'Hare is projected to grow 18 percent by 2010, the FAA said. During the same period, anticipated improvements in air-traffic technology and the use of more efficient arrival and departure procedures are projected to increase O'Hare's capacity by only about 6 percent.

"This imbalance between capacity and demand growth is expected to significantly increase delays at O'Hare," said the report, which FAA Administrator Jane Garvey will present Wednesday to the House Subcommittee on Aviation.

The findings are expected to fuel the call in Congress to impose a solution to the crisis on airlines that have resisted taking voluntary steps to reduce delays.

Mayor Richard Daley and Chicago Aviation Commissioner Thomas Walker declined to comment Tuesday on the findings until they are officially released. Midway Airport was not covered in the report.

Meanwhile, Illinois Transportation Secretary Kirk Brown, who is leading Gov. George Ryan's campaign to build a new airport near south suburban Peotone to improve airline service in the region, assailed Chicago officials for maintaining there is no capacity problem at O'Hare.

Brown said Tuesday in Springfield that it's time to "put their cards on the table" about what would be needed to build a new runway at O'Hare.

Both Ryan and Daley were scheduled to meet Wednesday in Washington with the Illinois congressional delegation, although aides for both men said the meeting was not related to the release of the airport capacity study and that the aviation issue was not on their agenda.

But as spring storms are prompting delays at O'Hare and across the nation, a solution to the threat of gridlock is on the minds of travelers.

Even when the weather is good for aviation—what the industry calls a "blue sky day"—airline over-scheduling at O'Hare causes air traffic to be at or above the capacity of the airport for 3½ hours of the 16-hour operational day, the FAA said in the report. In adverse weather, O'Hare faces problems for 8 hours of the day, routinely resulting in about 12 percent of all flights being delayed.

The so-called benchmarks that the FAA issued for each major airport detail the volume of flights that can be handled, without significant delays, during various times of the day, under a range of weather conditions and using different combinations of runways.

Inspector General Kenneth Mead of the U.S. Department of Transportation said the capacity benchmarks are "critical to understanding the true impact of airline scheduling practices and what relief can be expected from new technology and airport infrastructure enhancements."

Jack Ryan, an aviation operations expert at the Air Transport Association, said in prepared remarks expected to be delivered Wednesday to Congress that airline scheduling practices are not to blame for the record number of delayed and canceled flights. Ryan, whose organization represents most U.S. airlines, also criticized the usefulness of the runway capacity study, saying "the FAA's benchmarks do not help us to understand the impact of air-carrier scheduling."

U.S. Transportation Secretary Norman Mineta disagrees. Mineta has indicated he will take action to stop the slide toward aviation gridlock, using the capacity benchmarks as a guideline for forming solutions that could include the rationing of flights at some airports and new pricing schemes to discourage excessive flights at the busiest times of the day.

On a good-weather day without any other complications in the air-traffic system, O'Hare can accommodate about 50 arrivals and departures per 15-minute period, or about 200 operations per hour. But the FAA data show the airlines routinely exceed those numbers.

The effects of airline overscheduling on delays are even more apparent when air traffic controllers are forced to close some runways because of bad weather, reducing the hourly acceptance rate of aircraft destined for O'Hare.

Tribune staff reporter Rick Pearson contributed to this report from Springfield.