Mexicana Airlines pilots went on strike for more money, but service was reported normal after President Miguel de la Madrid ordered the 976 pilots to stay on the job . . . San Diego-based Imperial Corp. of America has agreed to sell its mortgage banking subsidiary, ICA Mortgage Corp., to San Francisco-based First Nationwide Bank, a unit of Ford Motor Co., for an undisclosed amount . . . Metromedia Co., Secaucus, N.J., said it has raised its stake in New York-based Orion Pictures Corp. to the equivalent of 19.2% of the common shares outstanding . . . H. F. Ahmanson & Co., of Los Angeles, said it completed its acquisition of Tucson Savings & Loan for an undisclosed amount of Ahmanson common stock.