WASHINGTON — The Justice Department has sued Sheriff Joe Arpaio of Arizona, asking a federal court to prevent the brazen and outspoken lawman from racially profiling Latinos, abusing them in his jails and retaliating against his critics.

“The police are supposed to protect and support our community, not divide them,” said Assistant Attorney General Thomas E. Perez, head of the Justice Department’s civil rights division. “This is an abuse of power case involving a sheriff and a sheriff’s office that has ignored the Constitution.”

The lawsuit, filed Thursday in U.S. District Court in Phoenix, alleges that Arpaio’s Maricopa County department engages in a “pattern of unconstitutional conduct” against Latinos, especially immigrants.

Justice Department officials in Washington are asking the court to name an independent monitor to oversee the sheriff’s office, develop reform policies to better staff the jails and patrol the county, and possibly find Arpaio and other top sheriff’s officials in contempt of court if they do not make changes in a community whose Latino population has grown by 47 percent over the last decade.

Arpaio did not immediately comment on the lawsuit. In the past Arpaio has said he would not be Washington’s “whipping boy” while the Justice Department plays politics to encourage Latino votes for President Barack Obama this fall.

One of Arpaio’s supporters, Andi Bell, who last month organized a community walk in his defense, said “everyone has been going after Joe Arpaio.”

But, Bell said, “The Department of Justice and the administration is not protecting us in Arizona. He is.”

The sheriff, who was warned in December that a lawsuit was coming if he did not clean up his jails and sheriff’s patrols, attempted to forestall the suit Wednesday by issuing a 17-page document called “Integrity, Accountability, Community” that addressed some of the issues.

But Perez called it “largely an admission of the problem.” He added, “This too-little, too-late document cobbled together beyond the eleventh hour is no substitute for meaningful reform.”

Arpaio has been resistant to change and sensitive to criticism during his 20 years as sheriff. But Perez warned the sheriff that he would resist the suit at his own peril.

“If Maricopa County wants to go to the mat and go to trial,” Perez said, “there is a lot at stake.”

The suit alleges that Arpaio allowed and encouraged his deputies to randomly profile Latino motorists, then transfer them to jail without apprising them of their legal rights.

“If you look Latino, you are too often fair game,” Perez said.

In one case, a Latina who is a U.S. citizen and was five months’ pregnant was stopped after she pulled into her driveway. She alleges that when she refused an order to sit on the hood of the car, she was slammed stomach-first three times onto the vehicle. Deputies next dragged her to a patrol car and locked her inside for 30 minutes without air conditioning, she said. She was cited for not providing identification.

Spanish speakers in the jails sometimes do not receive language assistance, the suit said, and at times detention officers “forced Latino prisoners with limited English skills to sign key legal documents printed in English, in which they forfeited key rights.”

The suit further contends that Arpaio and his sheriff’s office often retaliated against his critics, including judges, lawyers and community leaders in Arizona, subjecting them to “baseless” criminal actions, “unfounded” civil lawsuits and “meritless” administrative measures.

“Nobody is above the law,” Perez said, “and nobody can misuse the legal process to silence those with different opinions.”

Mary Rose Wilcox, a Maricopa County supervisor, said in an interview that she was indicted for voicing her opposition to the sheriff’s raids in her heavily Latino district. Asked about the lawsuit, she said, “People have been saying, ’Finally justice has come.’”

A separate Justice Department investigation is reviewing allegations of criminal corruption in the sheriff’s office.

The civil lawsuit Thursday describes a pervasive attitude that demeans Latinos and a sheriff who rules Maricopa County by blunt intimidation.

Arpaio said in a 2008 book that Mexicans were attempting the “reconquest” of American soil.

In a 2009 interview, he said many Latinos were leaving Phoenix because they feared him. “I think we’re doing something good, if they’re leaving,” he said.