The Supreme Court backed off Tuesday from strict enforcement of its historic Miranda decision, ruling that a crime suspect's words can be used against him if he fails to clearly tell police that he does not want to talk.

In the past, the court said the "burden rests on the government" to show that a crime suspect had "knowingly and intelligently waived" his rights. Some police departments tell officers not to begin questioning until a suspect has waived his rights, usually by signing a waiver form.

But in Tuesday's 5-4 decision, the court shifted the balance in favor of the police, saying a suspect has a duty to speak up and say he does not want to talk.

Moreover, the police are "not required to obtain a waiver" of the suspect's "right to remain silent before interrogating him," Justice Anthony M. Kennedy wrote.

In her first strongly written dissent, Justice Sonia Sotomayor said the ruling "turns Miranda upside down" and "marks a substantial retreat from the protection against compelled self-incrimination."

Some experts on police questioning said the court's subtle shift would be felt in station houses across the country.

"This is the most important Miranda decision in a decade. And it will have a substantial impact on police practices," said Charles Weisselberg, a law professor at UC Berkeley. "This decision approves of the practice of giving the warnings and then asking questions of the suspect, without asking first whether he wants to waive his rights."

The case decided Tuesday involved Van Thompkins, who was arrested a year after the shooting of two men outside a mall in Southfield, Mich. One of the men died.

A police detective read Thompkins his rights, including the right to remain silent and to have a lawyer. Thompkins said he understood, but did not sign a form.

For about two hours and 45 minutes, Thompkins said almost nothing in response to questions. The detective asked Thompkins if he believed in God and then asked: "Do you pray to God to forgive you for shooting that boy down?"

"Yes," Thompkins said, and looked away. He refused to sign a confession or to speak further, but he was convicted of first-degree murder, based largely on his one-word reply.

The U.S. 6th Circuit Court of Appeals overturned Thompkins' conviction on the grounds that the use of the incriminating answer violated his right against self-incrimination under the Miranda decision.

The Supreme Court reversed that ruling and reinstated the conviction.

A suspect who wants to invoke the right to remain silent must "do so unambiguously," Kennedy said. "Thompkins did not say that he wanted to remain silent or that he did not want to talk with the police. Had he made either of these simple, unambiguous statements, he would have invoked his right to cut off questioning."

Joining Kennedy to form the majority were Chief Justice John G. Roberts Jr. and Justices Antonin Scalia, Clarence Thomas and Samuel A. Alito Jr.

Kennedy has played a key role in the last decade in preserving the core Miranda rule, while also narrowing its practical effect. For example, he joined with the liberal bloc for a 5-4 ruling in 2004 that rejected the police tactic of questioning first and then warning a suspect of his rights only after he made an incriminating comment.

The same day, he joined a 5-4 ruling by the conservative side that said physical evidence, such as a gun or cash, could be used against a suspect even if he revealed it during questioning without Miranda warnings.

In the case decided Tuesday, Kennedy emphasized that the suspect had been warned of his rights and eventually chose to speak.

The California-based Criminal Justice Legal Foundation praised the justices for paring back the "artificial rule" set in the Miranda decision. The court "recognized the practical realities that the police face in dealing with suspects," said Kent Scheidegger, the group's legal director.

But Steven Shapiro, legal director for the American Civil Liberties Union, said the case "demonstrates the power of custodial interrogation to wear down the defendant's willpower, which is what Miranda was designed to prevent."

In her dissent, Sotomayor faulted the majority for announcing a "new general principle of law" that will be confusing in practice.

"Criminal suspects must now unambiguously invoke their right to remain silent - which, counterintuitively, requires them to speak," she said.

Joining her in dissent were Justices John Paul Stevens, Ruth Bader Ginsburg and Stephen G. Breyer.

The majority ruling is in line with the position taken by the Obama administration and Solicitor General Elena Kagan, who has been nominated to the Supreme Court.

In December, Kagan filed a brief on the side of Michigan prosecutors and argued that "the government need not prove that a suspect expressly waived his rights."