The federal government has spent years considering whether to take steps to help keep dangerous strains of E. coli bacteria out of the food supply, a question that has become even more urgent in the face of a deadly wave of E. coli sickness that swept through Europe and raised alarms on both sides of the Atlantic. Now, two major American companies, Costco Wholesale and Beef Products Inc., have gotten tired of waiting for regulators to act. They are proceeding with their own plans to protect customers. Last month, Costco, one of the nation