The Government Accountability Office also found that the government still lacks sufficient plans and training programs to prepare for catastrophic disasters like the Aug. 29 storm that devastated much of the Gulf Coast area.
Responding, a Homeland Security Department spokesman attacked the GAO's preliminary findings as "premature and unprofessional."
The GAO report, which marks the first congressional conclusions about the much-criticized federal response to Katrina, offered a harsh assessment of the government's preparations and reaction to catastrophic disasters. It also singled out Chertoff in several shortcomings.
The GAO report said that neither Chertoff nor any of his deputies in the disaster area acted as President Bush's overall storm coordinator, "which serves to underscore the immaturity of and weaknesses relating to the current national response framework."
Leadership "was unclear," the report found.
Because of the internal confusion, federal officials were indecisive and slow to realize Katrina was a catastrophic disaster, it said.
The report also noted that Chertoff declared Katrina an "incident of national significance" on Aug. 30, a full day after the storm hit. But Chertoff did not specifically classify the storm as a catastrophic disaster, which would have activated parts of the National Response Plan to trigger a faster response.
"As a result, the federal response generally was to wait for the affected states to request assistance," the report found.