TULSA -- If Armageddon leaves Oral Roberts' town unscathed, well, fine. But if it doesn't, American Airlines is ready.

This spring the airline opened its supersecure underground computer bunker -- a $34 million facility covered with five feet of dirt, built by the airline to be earthquake proof, terrorist proof, flood proof, Sherman tank proof, blackout proof, possum proof, fireproof, tornado proof and generally able to withstand any other type of assault.

Computer operations are big business for all airlines, but especially for American, which pioneered their use for reservations. American's Sabre system, begun with spectacular corporate foresight in 1958 as an internal reservations processing center and marketed to travel agents beginning in 1976, processes nearly half of the computer-booked airline reservations nationwide and is the largest on-line computer system outside the U.S. government.

And not only is it large -- it is extremely profitable. The system earned $336 million in revenue last year and produced profits of $142 million.

Not surprisingly, American has gone to great lengths to make sure its critical equipment doesn't go down.

American's computers handle reservations and ticketing for American and other airlines that pay for the service, serving more than 12,000 travel agencies worldwide. They also track mileage for American's frequent flyer program, dispatch and control aircraft and crews, keep a watch on spare parts and fuel consumption, determine the cost of the airline's seats and schedule and track 1,560 flights a day -- monitoring departures and arrivals and flight time. American also uses its computers to handle the company's accounting and payroll needs and for various types of research.

In all, the computers handle a staggering 53 million transactions or messages a day.

That makes corporate contingency planning for computers a critical issue. "American would have very serious difficulties operating more than eight or nine months without going out of business," without its computer operations, said George F. Maulsby, senior director for data processing and communications services for American.

American's computer operations were consolidated in Tulsa in the early 1970s, in a windowless building at the Tulsa airport. Then in 1983, the airline began planning for a more secure facility, rejecting such alternatives as keeping a duplicate system in another location.

Construction of the bunker took more than two years. The building was made to withstand earthquake shocks comparable to what might occur in the area of the San Andreas fault, despite its location in an area where earth tremors are infrequent and mild. In a tornado, the air pressure in the building can be adjusted to keep the building from blowing apart when the air pressure drops in the center of the storm.

Before an employe can enter the facility, he or she steps into a security booth. A machine in the booth reads the blood vessel pattern on the wall of the employe's retina -- a feature, like fingerprints, that can't be duplicated and that, unlike fingerprints can't be changed. The booth also weighs the employe, so another person can't step into the booth with the employe and follow him or her into the center. The door leading into the center will not open until the 800-pound door leading into the booth closes and locks behind the employe. Even getting into the booth requires an employe to use a computer-coded card and employe number.

"We think our computer center is more secure than most nuclear and military institutions," said Hani Rabi, manager of contingency planning for data processing and computer services.

American is still transferring its computers into the new facility, a task that is "kind of like changing an engine while you're flying," according to Maulsby. The computers that track flight operations are in the building, and the Sabre computerized reservation system is expected to be installed by the end of the year.

Not all of the airlines computers will be underground. The computers that handle accounting tasks will remain in the above-ground facility at the Tulsa airport, and the company is building another computer center in Dallas that will be used for writing new programs.

Inside the bunker, the ceilings are high, the colors are muted and an artificial skylight helps dispel the feeling of being underground. The center is designed to operate for three days without help from outside. It holds stockpiled food and water and there are cots and showers.

To enter the computer room inside the bunker requires passing through another security booth, and anyone who enters the center is tracked by cameras and audio recorders.