WASHINGTON — Two Supreme Court cases involving police searches of cellphones without warrants present vastly different views of the ubiquitous device.

Is it a critical tool for a criminal, or an American’s virtual home?

How the justices answer that question could determine the outcome of the cases being argued Tuesday. A drug dealer and a gang member want the court to rule that the searches of their cellphones after their arrest violated their right to privacy in the digital age.

The Obama administration and California, defending the searches, say cellphones are no different from anything else a person may be carrying when arrested. Police may search those items without a warrant under a line of high court cases reaching back 40 years.

What’s more, said Donald Verrilli Jr., the administration’s top Supreme Court lawyer, “Cellphones are now critical tools in the commission of crimes.”

Librarians, the news media, defense lawyers and civil liberties groups on the right and left are trying to convince the justices that they should take a broad view of the privacy issues raised when police have unimpeded access to increasingly powerful devices that may contain a wealth of personal data: emails and phone numbers, photographs, information about purchases and political affiliations, books and a gateway to even more material online.

“Cellphones and other portable electronic devices are, in effect, our new homes,” the American Civil Liberties Union said in a court filing that urged the court to apply the same tough standards to cellphone searches that judges have historically applied to police intrusions into a home.

Under the Constitution’s Fourth Amendment, police generally need a warrant before they can conduct a search. The warrant itself must be based on “probable cause,” evidence that a crime has been committed.

But in the early 1970s, the Supreme Court carved out exceptions for officers dealing with people they have arrested. The court was trying to set clear rules that allowed police to look for concealed weapons and prevent the destruction of evidence. Briefcases, wallets, purses and crumpled cigarette packs all are fair game if they are being carried by a suspect or within the person’s immediate control.

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.

In the two Supreme Court cases being argued Tuesday, one defendant carried a smartphone and the other an older and less advanced flip phone.

In San Diego, police found indications of gang membership when they looked through defendant David Leon Riley’s Samsung smartphone. Prosecutors used video and photographs found on the smartphone to persuade a jury to convict Riley of attempted murder and other charges. California courts rejected Riley’s efforts to throw out the evidence and upheld the convictions.

In Boston, a federal appeals court ruled that police must have a warrant before searching arrestees’ cellphones, and the administration is appealing that decision.