Travelers on France's superhighways will soon be able to dine on hamburgers at roadside fast-food restaurants. Burger King, in cooperation with the French restaurant and hotel company Elitair, announced plans Wednesday to open the first two fast-food restaurants at rest stops along the national highway network. One will be near Evry, southeast of Paris, on the A-6 highway. The other, a drive-through restaurant, will be near Bordeaux on the A-10 highway. Burger King also said the first fast-food hamburger restaurant at a French airport will open next month in a shopping area at Charles de Gaulle airport outside Paris.