The Wisconsin judge arrested last month and accused of helping an undocumented immigrant evade federal agents was indicted by a federal grand jury on Tuesday on charges of concealing a person from arrest and obstruction of proceedings.

The indictment of the judge, Hannah C. Dugan of the Milwaukee County Circuit Court, was a routine but significant step in the Justice Department’s case against her. The Trump administration has defended the prosecution as a warning that no one is above the law, while many Democrats, lawyers and former judges have denounced it as an assault on the judiciary.

Judge Dugan, who has been temporarily removed from the bench by the Wisconsin Supreme Court while the case against her advances, has indicated through a lawyer that she intends to fight the charges. She is expected to appear in court on Thursday.

“Judge Hannah C. Dugan has committed herself to the rule of law and the principles of due process for her entire career as a lawyer and a judge,” her lawyers said in a statement shortly after she was arrested. They added that she “will defend herself vigorously, and looks forward to being exonerated.”

The judge’s transformation from a little-known local jurist to a face of the national immigration debate began on April 18 with a pretrial hearing in a domestic abuse case against Eduardo Flores-Ruiz, a Mexican immigrant.

Several federal officials from different agencies had gathered in the hallway outside Judge Dugan’s courtroom and had planned to arrest Mr. Flores-Ruiz, who they said was in the country illegally, after his court appearance. The federal agents had told courthouse security officers and the judge’s courtroom deputy about their plans, according to an F.B.I. charging document.