ATLANTA — Bankruptcy can be a wake-up call for airlines about the need to run their operations more efficiently, but it also can shine a light on a more basic challenge: making customers happy.

UAL Corp.'s United Airlines and Delta Air Lines Inc., both of which restructured under Chapter 11 in recent years, ranked last and next to last, respectively, among airlines in terms of customer satisfaction in a survey to be released today by the University of Michigan.

Marks were only slightly better for AMR Corp.'s American Airlines, which teetered on the verge of bankruptcy before winning employee concessions in 2003, and Northwest Airlines Corp., which is currently in bankruptcy.

"The first step in improvement here is to recognize that something is wrong," said Claes Fornell, a University of Michigan business professor and director of the research center that compiled the data.

The airlines said they are working hard to improve the experience of their customers.

"We know the service is not where it should be as far as baggage delivery," said Betsy Talton, a spokeswoman for Atlanta-based Delta. "We're concentrating on that this year so that we see significant improvements."

Tim Wagner, a spokesman for Fort Worth, Texas-based AMR, said there isn't much the airlines can do when weather delays flights.

"The one thing we can do is focus on the things we can control, and that's our face-to-face interaction with customers," Wagner said.

There were some bright spots for a few airlines in the survey. Dallas-based Southwest Airlines Co. ranked first, and was one of only two airlines mentioned by name in the survey that improved in terms of customer satisfaction this year compared with last year. Houston-based Continental Airlines Inc. was the other.

"We've done as well as we have up to date by making sure our customers have a rich experience, and that's largely due to our people," said Beth Harbin, a spokeswoman for Southwest, which also is one of the few consistently profitable airlines.

About 20,000 people were asked during the first quarter of this year to rate their level of satisfaction as customers of companies in a variety of industries, including the airlines. An American Customer Satisfaction Index, on a scale of 1 to 100, was created based on the responses to questions about overall satisfaction, intention to be a repeat customer and perception of quality, value and expectations.

The index for the airline industry as a whole fell to 63 from 65 last year. Southwest had the highest index with 76, up from 74 last year. United's was the lowest at 56. Bringing up the rear was Delta at 59 and American at 60. Eagan, Minn.-based Northwest was only slightly better at 61.

"The same problems that have pulled airline passenger satisfaction down the past few years — disenchanted employees, increasing fuel costs, bankruptcy, and now also record levels of lost, delayed, and damaged luggage — cause it to drop again," the researchers said in their analysis.

UAL spokeswoman Robin Urbanski said the Elk Grove Village, Ill.-based parent of United knows it needs to do a better job giving customers what they expect.

"Work is under way to make this a priority," Urbanski said, adding that the airline appointed an executive last year to lead a new customer service division.

Talton said Delta, which exited bankruptcy on April 30, has added new in-flight entertainment and other products to give customers a better experience.

"The morale of Delta people has improved," Talton said. "We know that's important to our customers. That's not only what makes our business run smoothly, but it also is what provides a good experience to our customers."