NEW ORLEANS (Reuters) - The New Orleans Police Department too often uses excessive force, conducts illegal stops and arrests, and has a pattern of discriminating on the basis of race, gender and sexual orientation, the U.S. Justice Department said in a report on Thursday.

"For too long, the Department has been largely indifferent to widespread violations of law and policy by its officers," according to the report by the Justice Department's Civil Rights Division.

The report outlined problems with training, recruiting, supervision and interrogation practices.

It said the police department encourages under-investigating violence against women. It also found that officers used significant force against people with mental illness in cases in which it appeared no force was necessary.

"Instances of clearly unjustified force are routinely approved by supervisors and ratified up the chain of command, resulting in no accountability," the report said. "Officers even encourage each other to use force as retaliation."

Two days after taking office in May 2010, Mayor Mitch Landrieu requested federal help to reform the New Orleans Police Department and stanch the persistent high incidence of violent crime.

In December 2010, a federal jury convicted three current and former New Orleans police officers in the shooting death and burning of a man in the chaotic days following the devastating 2005 Hurricane Katrina. In March 2010, a former New Orleans police detective pleaded guilty to helping cover up two shooting deaths by police days after Katrina struck.

Federal prosecutors have charged 20 officers in four separate cases stemming from Katrina, according to media reports.

The Justice Department report recommended immediately suspending the use of dogs for apprehending suspects because the dogs were found to be so uncontrollable that they attacked their own handlers.

Federal officials also called for reforms that would improve training, foster better community collaboration and eliminate bias.

(Reporting by Kathy Finn and Corrie MacLaggan; editing by Peter Bohan and Mohammad Zargham)