ON NATIONAL television in 2009, Joe Arpaio, the elected sheriff of Maricopa County, Ariz., told an interviewer: “They hate me, the Hispanic community, because they’re afraid they’re going to be arrested. And they’re all leaving town, so I think we’re doing something good, if they’re leaving.”

Last week, just as the Justice Department was about to file suit to clean up what it describes as a pattern of anti-Hispanic discrimination and rampant abuse in his department, Mr. Arpaio was trying out a different line. “I do not tolerate racist attitudes or behaviors,” he pronounced, in a hastily prepared document designed, he said, to deepen public trust, “particularly as it relates to our Hispanic community.”

Mr. Arpaio, who runs one of the nation’s largest local law enforcement agencies, has made it his mission for at least six years to root out undocumented immigrants in Maricopa, a sprawling locality of 3.9 million people that includes the city of Phoenix. In the process, he has led a systematic campaign of harassment that always swept in Hispanic American citizens and legal residents, who constitute nearly a third of the county’s population.

In its lawsuit, the Justice Department’s Civil Rights Division details what amounts to a pattern of blatant racism in the 2,700-strong sheriff’s department. For example:

●Latino drivers are four to nine times more likely to be stopped by sheriff’s deputies than non-Latino drivers engaged in the same conduct, depending on the part of the county, according to the government’s complaint.

●The department’s human-smuggling unit, which routinely stops vehicles in search of undocumented immigrants, is far more likely to stop those occupied by Latino drivers, the “vast majority” of whom are U.S. citizens or lawfully present in the country, according to the government lawsuit.

●Complaints of mistreatment of Hispanics during traffic stops are common. In one incident described by the government, a Latina — a U.S. citizen who was five months pregnant — was stopped by a sheriff’s deputy as she pulled into her own driveway, grabbed by the officer, slammed repeatedly into the vehicle and shoved into the back of the patrol car, where she was made to sit for a half hour without air conditioning. The woman was subsequently issued a ticket for failing to provide proof of insurance — which she ultimately did provide in court.

The shock value of such incidents is mitigated slightly by the fact that reports of similar ones are commonplace, as are allegations that jail officers (also part of Mr. Arpaio’s realm) routinely make reference to “wetbacks” and “Mexican bitches.”

The Justice Department spent several months trying to reach an accommodation with Mr. Arpaio that would have included a commitment to broad reforms, along with the appointment of a mutually agreed-on federal monitor. Mr. Arpaio’s stonewalling led to the lawsuit, which seeks to force reforms by threatening to suspend more than $3 million in annual federal aid.

Playing to the gallery, Mr. Arpaio declared his department won’t submit to a federal takeover. He released a document — based partly on the Justice Department consent decree he refused to sign — pledging long-overdue changes.

That’s a fine public relations strategy, but it doesn’t make a dent in the reality of a deeply troubled department. As the Justice Department concluded, only a lawsuit will achieve that.