WASHINGTON — The Justice Department on Thursday opened an investigation into the Louisiana State Police over accusations that officers had engaged in abusive and discriminatory behavior, including the fatal beating of a Black motorist three years ago.

Under President Biden and Attorney General Merrick B. Garland, the department has expanded its use of such intensive inquiries, known as pattern-or-practice investigations, which are meant to determine whether a state or local law enforcement agency uses “excessive force, biased policing and other unconstitutional practices.”

The investigation, to be conducted by the department’s Civil Rights Division, was opened after a preliminary review included reports of officers repeatedly using excessive force, often against people pulled over for minor traffic offenses, who were “already handcuffed” or were “not resisting” arrest, Assistant Attorney General Kristen Clarke told reporters in Baton Rouge, La., on Thursday.

The department also received reports that officers had targeted Black residents and people of color, including “disturbing information about the use of racial slurs and racially derogatory terms,” she said.

Ms. Clarke is currently overseeing similar investigations into the Minneapolis Police Department in connection with the killing of George Floyd, the Louisville Police Department’s actions leading up to the shooting of Breonna Taylor in Kentucky, and other investigations of police conduct in Phoenix and Mt. Vernon, N.Y.

The investigation in Louisiana was prompted by two brutal beatings, both captured on video, that occthree years ago, inciting an outcry from civil rights leaders.

In May 2019, Ronald Greene was pulled over by white officers, shackled, stunned with a Taser, put in a chokehold and punched in the face. The troopers then left him handcuffed and face down for more than nine minutes. He later died.

The police originally claimed he had been resisting arrest, but The Associated Press later published body camera footage of a bloodied Mr. Greene, 49, pleading with them, saying: “I’m your brother! I’m scared!”

Mr. Greene’s death was ruled accidental and was attributed to cardiac arrest, Renee Smith, the Union Parish coroner, told The A.P., adding that his file mentioned the car crash but not a struggle with the police.

The family commissioned an independent autopsy that found severe injuries to Mr. Greene’s head and skull, and several wounds to his face.

Three weeks later, a white officer with the Louisiana State Police attacked another Black motorist, Aaron Larry Bowman, after a routine traffic stop in Monroe, slamming a heavy flashlight repeatedly into Mr. Bowman’s head and chest and leaving him with a broken jaw, broken ribs and head lacerations.

The trooper, Jacob Brown, 31, of Rayville, La., was arrested last year on charges of aggravated second-degree battery and malfeasance in office, and later quit the force.

Mr. Bowman reacted to the news of the investigation by first expressing his gratitude, then asking, “Does this mean I’ll get justice soon?” according to his lawyer, Donecia Banks-Miley.

“He was obviously targeted and stereotyped and brutalized,” Ms. Banks-Miley said. “We asked the Justice Department to look into this last year. It took them a little while, but we are very happy they will investigate this.”

On Thursday, Ms. Clarke was joined by Louisiana state officials, including Gov. John Bel Edwards, and two top state police officials, who pledged to cooperate with the inquiry.

The investigation is separate from a federal criminal investigation of troopers on the police force.

The results of a pattern-and-practice inquiry can be used in civil litigation against local departments. More often, they are used as a starting point for a settlement agreement, which includes significant reforms to policing and hiring practices and a mechanism for monitoring a department’s compliance.

“This investigation, like all of our pattern or practice investigations, will seek to promote the transparency, accountability and public trust that is essential to public safety,” Mr. Garland said in a statement.