Chances are that Lockheed Martin Corp., Boeing Co., and Raytheon Co.-- all U.S.-based aerospace firms -- will soon confront a tough new European competitor. But France's Arospatiale apparently won't figure into the firm that's being created by British and German companies. Impatient with France's reluctance to privatize state-owned Arospatiale, their condition for welcoming it as a partner, British Aerospace PLC and Germany's Daimler-Benz Aerospace now say they plan to merge early in 1999.