Sales of German cars in the United States, traditionally a strong market, declined significantly in January. Volkswagen reports it sold about 3,500 fewer automobiles than a year ago. Volkswagen subsidiary Audi also reported for a sales loss of about 13 percent during the same period, and Porsche said sales in the U.S. fell 10 percent. The only German carmaker to report sales gains during January was DaimlerChrysler.