LEAD: British Aerospace P.L.C. said today that a four-nation consortium of which it is a member had been awarded a contract to develop a new fighter plane. The contract is worth about $10 billion.

British Aerospace P.L.C. said today that a four-nation consortium of which it is a member had been awarded a contract to develop a new fighter plane. The contract is worth about $10 billion.

British Aerospace said the contract was signed Wednesday in Munich, West Germany, by the NATO European Fighter Aircraft Management Agency, representing Britain, Spain, Italy and West Germany.

The contract calls for the development of the aircraft and its armament. It is scheduled to come into service in the air forces of the four countries in the mid-1990's.

Britain's Ministry of Defense said Britain would have a 33 percent share of the project, the biggest West European arms project since World War II. The new plane would replace Phantoms and Jaguars in the Royal Air Force, it said.

The other companies participating in the program are Casa of Spain, Messerschmitt-Bolkow-Blohm G.m.b.H. of West Germany and Aeritalia of Italy.

Rolls-Royce P.L.C. said earlier that the Eurojet consortium, comprising companies in the same four countries, had been awarded a contract to develop the European fighter's engine in a deal worth $1 billion.