WASHINGTON — The Supreme Court agreed Friday to decide whether police need a warrant to search the cellphones of people they have arrested.

The court will hear two cases in which criminal defendants were convicted and sentenced to lengthy prison terms at least in part on the strength of evidence obtained by warrantless searches of their cellphones.

The high court ruled 40 years ago that police don’t need a search warrant to look through anything a person is carrying when arrested.

But lower federal and state courts have differed over whether that decision, predating the digital age, should apply to increasingly sophisticated cellphones, including even more advanced smartphones.

The cases will be argued in April and decided by late June.

More than 90 percent of Americans own at least one cellphone, the Pew Research Center says, and the majority of those are smartphones — essentially increasingly powerful computers that are also telephones.