Four major European airlines that have joined together to develop a computer reservation system said yesterday that they will buy the software and technical support they need from a Texas Air Corp. subsidiary.

The European consortium said it will spend $300 million developing the Amadeus Corp. -- the name it has chosen for its computer reservation system -- but did not reveal how much of it would be with System One Corp., the Texas Air subsidiary. A System One spokeswoman said it would be in "the tens of millions."

System One competed against American Airlines' Sabre system to work with the European airlines on the computer reservation system. American had held out for a partnership that would have allowed it to collect transaction and leasing fees from the system when it began operating, according to an American spokesman.

Amadeus includes Air France, Iberia, Lufthansa and SAS airlines. Together they account for about 60 percent of the market for scheduled flights from one European country to another.

Another group of European carriers that includes British Airways, KLM Royal Dutch Airlines and Swissair announced earlier this month that it would join forces with United Air Lines to create a competing computer reservation system.

Europe is as large a market for air travel as the United States, which makes the U.S. airlines that have major computer reservation systems anxious to play a role in the development of more sophisticated automated reservation systems there.

Computer reservation systems have become major marketing tools and major profit centers for the airlines that operate them.

System One said yesterday that the new Amadeus system and its own system will be linked, allowing 15,000 travel agencies in the United States, Europe, Africa, the Bahamas, the Caribbean and in Central and South America to have equal access to both systems.

Eva Archer-Smith, a spokeswoman for System One, said the company had not sought an equity position in the European company. She said Amadeus and System One would not compete with each other in the United States or in Europe and that the two companies would support each other.

"In South America, for instance, where we have System One subscribers, we would encourage a conversion to Amadeus," she said. In other parts of the globe, Amadeus would encourage travel agents to use System One.

Under the agreement System One will license the European company to use its software and will provide technical and training support to tailor the system to the needs of Amadeus.