Federal officials have reached a temporary agreement to ease congestion at Chicago's O'Hare International Airport (search) by an estimated 20 percent by the end of the year.

The deal calls for a reduction of 37 daily arrivals -- 20 by United Airlines and 17 by American Airlines, officials said Wednesday in a conference call with congressional aides.

"We're definitely solving the problem of excessive delays at the nation's busiest airport," Federal Aviation Administration (search) official Sharon Pinkerton said.

Pinkerton said the order would be in effect from Nov. 1 through April. Details were being announced at an O'Hare news conference.

"We've worked hard to balance the need to provide vibrant air service and grow the economy with the need to clear the skies over O'Hare," Transportation Secretary Norman Y. Mineta (search) said in a statement. "The process worked, yielding substantial reductions that will produce results for the traveling public."

Sixteen airlines participated in three days of negotiations in Washington earlier this month held by the FAA, which has been trying to ease persistent delays at O'Hare that they say hamper the nation's entire air system. One-third of all flights at the airport are delayed.

Mineta had said the meeting was the last opportunity for airlines to voluntarily solve O'Hare's gridlock before the government would impose strict flight caps (search).

Together, United and American handle 88 percent of all flights at the Chicago airport. They had offered to support temporary flight caps, but they wanted other carriers also to make schedule cuts as well.

Under the new agreement, all the airlines agreed to a voluntary limit of 88 scheduled arrivals per hour during the peak hours between 7 a.m. and 8 p.m., according to the FAA. Previously, federal transportation officials had discussed a limit of 86 arrivals.

Another part of the agreement affects four airlines that have eight arrivals or fewer per day at O'Hare -- Alaska Airlines, America West, Spirit Airlines and USA 3000. Each will be allowed to increase their number of arrivals to eight per day but will not be allowed more than one additional arrival between noon and 8 p.m.

The FAA said in addition to the schedule reductions, airlines must contact the agency for approval prior to rescheduling flights, in order to ensure potential scheduling moves do not negatively effect airport efficiency.

Pinkerton estimated that the agreement would reduce delays at O'Hare by about 20 percent and cut delays by about 5 percent across the rest of the national network.

The long-term solution to the problem will be to add more capacity at O'Hare, Pinkerton said. She said the FAA is reviewing the city's proposed expansion plans for the airport.

Chicago-based United and Fort Worth, Texas-based American had already announced in January a voluntary 5 percent reduction in daily flight schedules between 1 p.m. and 8 p.m., the peak time for departures and arrivals.

Still, O'Hare remained near or at the bottom nationally in on-time performance.

In June, an extra 2 1/2 percent reduction took effect. The total came to about 90 fewer flights a day for the two airlines.

About two-thirds of arrivals at O'Hare have been on-time this year, compared with the FAA's systemwide goal of 82 percent.