It's hard to make an airline blush. Passenger complaints about poor service, crowded planes and even cancellations seldom produce more than a shrug from behind the ticket counter.

But the situation at Chicago's O'Hare International Airport has become so bad in the past six months that both United and American airlines felt compelled to publicly apologize to their best customers for the awful service they've been getting.

United even went so far as to give a 2,500-mile bonus to every one of its 970,000 premier frequent-flier members who flew "in, out or through" O'Hare since April 1--along with a letter of apology from its new chairman, James Goodwin, about the "drastic delays" they may have experienced at the airport during that time.

"Since you have recently traveled through our largest hub and United's hometown, you may have experienced drastic delays at Chicago's O'Hare International Airport," Goodwin wrote. "These delays have been largely due to unpredicted obstacles during renovations required by the ATC [air traffic control systems] and the coordination of their efforts in providing pleasant, efficient service." United accounts for about 40 percent of O'Hare's traffic.

American, which provides about a third of the flights at O'Hare, said it has had a similar experience at the Chicago airport but has taken a less costly approach in an effort to soothe its best frequent-flier customers. American has limited its apologies to letters to its best customers on specific flights that were delayed or canceled.

Jim Davidovich, marketing manager for United's Mileage Plus program, said about one-third of the airline's Premier card holders--those who travel at least 25,000 miles a year--received the mileage bonus. Davidovich wouldn't say how much the added miles were costing the airlines, only that it was "an expensive proposition."

United isn't offering anything--not even a written apology--to any of its other passengers, including Mileage Plus members who haven't achieved Premier status. "To do it [offer bonus miles] for all passengers would have been prohibitive," Davidovich said.

Davidovich said Goodwin came to him shortly after becoming chairman July 13 and said he wanted to do something to help compensate their best customers for the delays and cancellations they had experienced at O'Hare during the first half of the year.

In a July 15 speech to the Chicagoland Chamber of Commerce, Goodwin called the situation at O'Hare "a recipe for chaos." He said the chronic air traffic delays the airline has been suffering "are killing us."

During the first six months of the year, United has been forced to cancel or delay 4,677 flights at O'Hare because of either weather or air traffic control problems, the equivalent of shutting down the airline's operations at O'Hare for 10 days. Systemwide, Goodwin said delays and cancellations were costing United $10 million to $20 million a month.

The situation for American is not much better. During the first six months this year, American was forced to cancel or delay 2,645 flights, the equivalent of an eight-day shutdown at O'Hare and a tripling of the number of cancellations for the same period the previous year.

The Federal Aviation Administration announced last week that it would take actions to help cut back on the number of delays and cancellations. The actions, mostly technical, would give the FAA control center at Herndon more authority to make decisions nationwide on such things as holding flights on the ground and the minimum in-flight distances between aircraft in the hopes of speeding operations.

But the idea of giving its best customers bonus frequent-flier miles never left the hangar at American, nor has the airline issued a blanket apology to its passengers. Instead, according to spokeswoman Mary Frances Fagan, the Fort Worth-based airline sends letters to members of its Advantage Gold and Platinum frequent-flier club as the airline receives lists of canceled flights. "We send the letters when there's been a problem on a flight," she said. Fagan said the airline has been sending such targeted letters to its best customers for the past two years.