PHOENIX — A federal lawsuit asserting a “pattern of unlawful discrimination” by law enforcement officials here claims that Latinos at the county jail were often referred to as “stupid” or addressed with a coarse ethnic slur. It also says that an e-mail circulated among jail officers contained a photograph of a Chihuahua in a swimsuit, over the words, “A rare photo of a Mexican Navy Seal.”

On the streets, Latino drivers were five to nine times more likely than their non-Latino counterparts to be stopped or searched, the suit asserts, for appearing disheveled or dirty or if it was deemed that too many people were in the back seat. Some were detained because they were said to have looked nervous or avoided eye contact.

The accusations are among those included in a lawsuit filed by the Justice Department on Thursday against Sheriff Joe Arpaio of Maricopa County, who, calling himself “America’s toughest sheriff,” has waged a relentless crackdown on illegal immigrants.

The litigation, in an election year, escalates a politically charged fight over local enforcement of federal immigration laws and the civil rights of Latinos. The suit asks a federal judge to issue an order against discriminatory practices by sheriff’s deputies, and to require the Sheriff’s Office to eliminate a “pattern or practice of unlawful conduct.”