Delta Air Lines Inc. has ordered or taken options on 215 new aircraft, dividing the order betweeen McDonnell Douglas Corp. and Boeing Co. in deals that could total $10 billion.

The massive order, which had been hotly contested by the major aircraft and engine manufacturers, is to replace aging parts of Delta's fleet. Delta, with around 380 planes, is the nation's fourth-largest airline in terms of passenger-miles flown.Delta placed firm orders for nine MD-11 aircraft manufactured by St. Louis-based McDonnell Douglas Corp. and nine Boeing 767-300R planes. It said the order, including spare parts and engines, is worth $1.75 billion.

In addition, Delta took out options on another 31 MD-11s and 16 other Boeing 767 jets, as well as options on 100 MD-88s manufactured by McDonnell Douglas and 50 Boeing 757-232s.

Industry experts put the value of the McDonnell Douglas contract at over $6 billion, if all the options are exercised. But the company would not confirm or deny the figure.

The Boeing orders would be worth an estimated $4 billion, but a company official stressed that the figure was only speculation since Delta may not exercise all its options.

Delta also said that Pratt & Whitney had won the orders to provide engines for both sets of planes, beating out competition from General Electric Co. and Rolls-Royce Plc.

"The competition among the airplane and engine manufacturers was keen," Delta said.

Industry analysts had expected Delta to purchase either the MD-11 or Boeing 747 as a new long-distance wide-body aircraft. The 767 is a smaller long-range aircraft.

The order gives a big boost to McDonnell Douglas, which has been fighting to keep pace with Boeing and the European consortium Airbus Industrie.

Seattle-based Boeing, the world leader in commercial aviation with an estimated 50 percent of the market, has already garnered a record number of orders for planes this year.

Boeing's biggest order ever was a $4.6 billion purchase of 100 planes by International Lease Finance Corp., an airline leasing company, in May.

"These new orders and options announced today highlight our international and domestic growth plans and commitment to maintaining the most modern fleet of aircraft available," Delta said in announcing the orders.

Delta said the orders and options are in addition to 42 Boeing 757-200s, 12 Boeing 767-300s and 85 McDonnell Douglas MD-88s remaining from previously announced orders and options.

Delta could easily afford a major purchase of jetliners because it is in strong financial shape, airline analysts said.