The police do not need a warrant to enter a home if they smell burning marijuana, knock loudly, announce themselves and hear what they think is the sound of evidence being destroyed, the Supreme Court ruled on Monday in an 8-to-1 decision.

The issue as framed by the majority was a narrow one. It assumed there was good reason to think evidence was being destroyed, and asked only whether the conduct of the police had impermissibly caused the destruction.

Justice Samuel A. Alito Jr., writing for the majority, said police officers do not violate the Fourth Amendment's ban on unreasonable searches by kicking down a door after the occupants of an apartment react to hearing that officers are there by seeming to destroy evidence.

In dissent, Justice Ruth Bader Ginsburg wrote that the majority had handed the police an important new tool.

"The court today arms the police with a way routinely to dishonor the Fourth Amendment's warrant requirement in drug cases," Justice Ginsburg wrote. "In lieu of presenting their evidence to a neutral magistrate, police officers may now knock, listen, then break the door down, never mind that they had ample time to obtain a warrant."

The case, Kentucky v. King, No. 09-1272, arose from a mistake. After seeing a drug deal in a parking lot, police officers in Lexington, Ky., rushed into an apartment complex looking for a suspect who had sold cocaine to an informant.

But the smell of burning marijuana led them to the wrong apartment. After knocking and announcing themselves, they heard sounds from inside the apartment that they said made them fear that evidence was being destroyed. They kicked the door in and found marijuana and cocaine but not the original suspect, who was in a different apartment.

The Kentucky Supreme Court suppressed the evidence, saying that any risk of drugs being destroyed was the result of the decision by the police to knock and announce themselves rather than obtain a warrant.

The United States Supreme Court reversed that decision on Monday, saying the police had acted lawfully and that was all that mattered. The defendant, Hollis D. King, had choices other than destroying evidence, Justice Alito wrote.

He could have chosen not to respond to the knocking in any fashion, Justice Alito wrote. Or he could have come to the door and declined to let the officers enter without a warrant.

"Occupants who choose not to stand on their constitutional rights but instead elect to attempt to destroy evidence have only themselves to blame," Justice Alito wrote.

Justice Alito took pains to say that the majority was not deciding whether an emergency justifying an exception to the warrant requirement - an "exigent circumstance," in legal jargon - actually existed. He said that the Kentucky Supreme Court "expressed doubt on this issue" and that "any question about whether an exigency actually existed is better addressed" by the state court.

All the United States Supreme Court decided, Justice Alito wrote, was when evidence must be suppressed because the police had created the exigency. Lower courts had approached that question in some five different ways.

The standard announced Monday, Justice Alito wrote, had the virtue of simplicity.

"Where, as here, the police did not create the exigency by engaging or threatening to engage in conduct that violates the Fourth Amendment," he wrote, "warrantless entry to prevent the destruction of evidence is reasonable and thus allowed."

But "there is a strong argument," Justice Alito added, that evidence would have to be suppressed where the police did more than knock and announce themselves. In general, he wrote, "the exigent circumstances rule should not apply where the police, without a warrant or any legally sound basis for a warrantless entry, threaten that they will enter without permission unless admitted."

Justice Ginsburg, dissenting, said the majority had taken a wrong turn.

"The urgency must exist, I would rule," she wrote, "when the police come on the scene, not subsequent to their arrival, prompted by their own conduct."

Justice Ginsburg then asked a rhetorical question based on the text of the Fourth Amendment.

"How 'secure' do our homes remain if police, armed with no warrant, can pound on doors at will and, on hearing sounds indicative of things moving, forcibly enter and search for evidence of unlawful activity?" she asked.