Lawmakers were also sharply critical of the C.D.C.’s response. A memo by the subcommittee detailed a series of lapses, including that one of the anthrax labs was not properly secured on the day the release became known, so people tracked in and out. Workers had not been trained in how to decontaminate the lab, and no one knew who was in charge of decontamination. The clinic to care for potentially exposed employees was overwhelmed, physical exams were delayed and yet clinic officials did not request more staff members. Once the accident was recognized, the amount of anthrax bacteria involved and its location were not recorded.

Dr. Frieden testified that one of his agency’s mistakes was its failure to activate the emergency operations center that it normally uses when it responds to disasters like hurricanes, flu epidemics and severe outbreaks of food-borne disease. Using the center would have led to a better and more organized response, he said.

An outside expert who testified, Richard H. Ebright, a molecular biologist and laboratory director from Rutgers University, said the C.D.C. funds and conducts research, and also regulates it and oversees its safety — a serious conflict of interest, he said. He recommended that an independent agency be established to regulate research with dangerous organisms.

Asked by a subcommittee member how he would deal with a lab worker who made a serious safety mistake, Dr. Ebright said there would be consequences, possibly even termination.

Sean Kaufman, a former C.D.C. employee who is now president of a company that teaches lab safety, warned against penalizing researchers who made errors. Punishing individuals would lead others to try to cover up the truth and hide their mistakes, which could ultimately cause greater harm. A better response, Mr. Kaufman said, would be to improve training and procedures, to minimize human error.