WASHINGTON — Attorney General Merrick B. Garland has revised rules governing the use of force by law enforcement agencies overseen by the Justice Department, requiring federal agents to intervene when they see officials using excessive force or mistreating people in custody.

The rule change was circulated on Friday and posted on the department’s website on Monday — two days before the second anniversary of the death of George Floyd, who died beneath the knee of a Minneapolis police officer as other officers looked on.

“It is the policy of the Department of Justice to value and preserve human life,” Mr. Garland wrote in the four-page memo. “Officers may use only the force that is objectively reasonable to effectively gain control of an incident, while protecting the safety of the officer and others.”

The changes represent the first revision of the department’s use-of-force policy in 18 years. It now requires officers to “recognize and act upon the affirmative duty to intervene to prevent or stop, as appropriate, any officer from engaging in excessive force or any other use of force that violates the Constitution, other federal laws or department policies on the reasonable use of force.”

The existence of the memo was reported earlier by The Washington Post.

The new rules will apply to the Justice Department’s entire work force, including agents and officers with the F.B.I., the Drug Enforcement Administration, the U.S. Marshals Service, the Federal Bureau of Prisons and the Bureau of Alcohol, Tobacco, Firearms and Explosives.

The department does not have the authority to impose the requirements on local police forces or sheriff’s departments, though the Biden administration intends for the document to be used as a template for localities.

The use-of-force rules, rewritten in consultation with civil rights groups after the Floyd killing, also draw heavily from the National Consensus Policy on Use of Force, which was drafted by 11 major law enforcement groups representing federal, state and local law enforcement officers.

Other provisions include prohibitions against firing a weapon at a moving vehicle with the sole purpose of stopping it, and discharging a warning shot “outside of the prison context.”

The new memo is far more explicit and prescriptive than prior guidelines on the rights and physical well-being of people pursued in connection with crimes or taken into federal custody.

Federal officers not only have a responsibility to stop acts of police brutality, but also now have “the affirmative duty to request and/or render medical aid, as appropriate, where needed,” according to the guidelines.

The Department of Homeland Security, which is not governed by the Justice Department, enacted a similar rule in 2018, advising its employees to seek medical attention “as soon as practicable following a use of force and the end of any perceived public safety threat.”

The Justice Department memo is one in a series of actions taken by the Biden administration in the wake of the death of Mr. Floyd and several other episodes of police brutality.

In April 2021, Mr. Garland announced a wide-ranging investigation into the patterns, practices and culture of the Minneapolis Police Department after the former officer Derek Chauvin was found guilty of murdering Mr. Floyd.

“Nothing can fill the void the loved ones of George Floyd have felt since his death,” Mr. Garland said at the time. “My heart goes out to them and to all those who have experienced similar loss.”