In a 139-page filing with the Department of Transportation yesterday, Delta Air Lines Inc. accused American Airlines Inc. of competing unfairly by biasing its Sabre computer reservations system against competitors' flights.

Delta charged that American maintains two separate flight schedules in competitive markets -- one for actual flight operations and one for use in Sabre, other computer reservations systems (CRS) and public schedules.

The published schedules shorten the actual flight time, Delta said, giving American flights higher priority on most CRSs, including Sabre.

"American's actions substantially injure air transportation competition, violate the antibias provisions of the carrier-owned computer reservation systems regulations and constitute unfair and deceptive practices and unfair methods of competition," the complaint states.

An American Airlines spokesman said company officials have not had time to study the Delta filing, but denied any wrongdoing.

"We don't see how this suit can have any basis in fact," said Lowell Duncan, American vice president for corporate communications. "American has lived up to the letter and the spirit of the CRS regulations adopted in November 1984."

Delta charges that American's in-house schedule is used for allocation of resources, planning of airline operations, calculation of pilot and flight attendant pay and scheduling. Its published schedule -- usually with a shorter flight time -- is used to get higher priority on the computer systems, Delta said.

"American's Sabre bias scheme began before the ink was dry on government rules adopted in 1984 which outlawed such practices," Delta said. "American's current practices continue the very injuries to competition and consumers that were found to be the direct result of overt CRS display bias."

The Civil Aeronautics Board in 1984 ruled that airlines owning CRS were using bias in those systems to gain unfair advantage over their competitors. At that time, it set rules to govern computer reservation systems, stating for the first time that CRS owners could not discriminate in fees charged competitors or in the display of competitors' flights. That regulation set a system for ranking flights, taking into account departure time, arrival time and length of flight.

Sabre is the largest CRS, closely followed by United Air Lines Inc.'s Apollo system. Most travel agencies use either Sabre or Apollo, and 50 percent of CRS bookings are made from the first available flight displayed on the system, Delta's filing stated.

Delta charges that a dual schedule system allows American to "siphon off from Delta and other carriers" a substantial amount of revenue each year "through its new bias scheme." In what it says is a conservative estimate, Delta said American diverts about $120 million a year in revenue from competitors through the dual schedule system.

Delta, which owns and operates a smaller Datas II CRS, is a participating carrier in Sabre. It discloses its flight schedules, fares and seat availability to Sabre for listing, and pays American $1.75 per flight segment booked through the system.

American made a $140 million operating profit from Sabre last year.

As part of its evidence filed with DOT yesterday, Delta included correspondence between C. A. Pasciuto, America's vice president for employe relations, and Joann Donovan, former president of American's flight attendants' union. The letters make mention of "adjusted scheduled flight time" and the "historical actual time" and how the changes might affect flight attendant pay.