U.S. President Barack Obama has issued new rules on when terrorist suspects can remain in the custody of civilian authorities, instead of being transferred to the military.

The new rules, outlined in a memo Tuesday, essentially override a law that requires military detention for terrorists captured when plotting to attack the United States, by elaborating on a clause granting a presidential waiver.

Mr. Obama calls on the attorney general — or any designated, congressionally confirmed Justice Department official — to screen every terrorist suspect arrested by the FBI or other civilian agency. He grants the attorney general or his delegate the right to make case-by-case determinations or to designate entire categories of suspects or crimes for which military transfers would not be required.

The memo also creates seven “automatic waivers” from the military detention requirement. These include when officials determine that transferring the suspect to the military could “impede counterterrorism cooperation” with other countries, or could interfere with efforts to get the suspect to cooperate with authorities or confess.

There also are waivers for any permanent resident arrested in the U.S. or for activities in the U.S., and for anyone transferred to federal custody by state and local authorities.

Mr. Obama opposed the law requiring military detention, saying the military, law enforcement officials and intelligence agents need flexibility to act on a case-by-case basis in dealing with terror suspects.