Public health officials have linked recalled ground beef to illnesses from a rare strain of E. coli, the first such linkage to that strain in this country, adding fuel to an already fierce debate over expanding federal rules meant to keep the toxic bacteria out of the meat supply. Cargill Meat Solutions recalled 8,500 pounds of hamburger Saturday after investigators determined that it was the likely source of a bacterial strain known as E. coli O26, which had sickened three people in Maine and New York. Under federal rules, it is illegal to sell ground beef containing a more common strain of the bacteria, E. coli O157:H7, which has been responsible for thousands of illnesses, many deaths and the recall of millions of pounds of beef over the years. But federal regulators are now considering whether to give the same illegal status to at least six other E. coli strains, including O26, which can also make people violently sick. The meat industry has opposed such a change, saying it is not needed. Among the arguments the industry has used was one stubborn fact: no outbreak in this country from the rarer strains of E. coli had ever been definitively tied to ground beef. That is an argument the industry can no longer make. The federal Agriculture Department has been trying for several years to decide what to do about the additional strains of E. coli. The issue now falls in the lap of the Obama administration's new head of food safety at the department, Dr. Elisabeth Hagen, who was appointed last month. In a written statement provided to The New York Times, Hagen said 'In order to best prevent illnesses and deaths from dangerous E. coli in beef, our policies need to evolve to address a broader range of these pathogens, beyond E. coli O157:H7.' The agency has said that it is reluctant to make additional forms of toxic E. coli illegal in ground beef until it has developed a rapid test that can detect those strains in packing plants. Such tests are not expected to be ready until at least late next year. The beef industry argued against declaring the additional E. coli strains illegal in an Aug. 18 letter that the American Meat Institute, a trade group, sent to the agriculture secretary, Tom Vilsack. 