Starbucks Corp. announced yesterday it will begin taking steps to eliminate artificial growth hormones from the dairy products it serves. Food and Water Watch, a Washington-based environmental watchdog group, had been campaigning to get the company to stop using and selling products that contain the controversial hormone rBGH. The dairy products involved include fluid milk, half-and-half, whipped cream and eggnog. Initially, the changeover will affect the 5,500 company-owned stores in the United States, though some 3,000 franchised locations are also being looked at, according to company officials. Some market areas already have rBGH-free products, including New England and Southern California. The decision follows the recent announcement that Starbucks was eliminating trans fats from its food products.