The investigation will be carried out by the U.S. Attorney's Office in New Orleans, along with the Justice Department's Civil Rights Division, First Assistant U.S. Attorney Jan Mann said Friday.
The results of a state investigation have already been turned over to the Orleans Parish district attorney.
Several hundred evacuees claimed that police from suburban Gretna blocked them as they tried to flee New Orleans for safety on Sept. 1.
Many of the evacuees, who had been stranded at the New Orleans convention center without food and water, said they were told to cross the bridge to be evacuated from the city. But Gretna police confronted them on the bridge and forced them to turn around.
Police later said they blocked the evacuees because there were no supplies or services for them on the other side of the river.
The case raised widespread allegations of racism and spurred two marches across the bridge by national civil rights organizations in the months after the hurricane.
Gretna, a town of 17,500 across the Mississippi River from New Orleans, is almost two-thirds white. New Orleans is two-thirds black.
Orleans Parish District Attorney Eddie Jordan plans to present the results of a state attorney general's investigation to a grand jury. Jordan has declined to reveal any details of the report.
Gretna Police Chief Arthur Lawson has acknowledged that his officers fired shots into the air during the blockade in an attempt to quell what he described as unrest among the evacuees.
The American Civil Liberties Union has been pressing state Attorney General Charles Foti to make his investigative report public. Louisiana ACLU executive director Joe Cook said Friday he was disappointed that the report had not been released.