A unanimous Supreme Court decision upheld yesterday a police department’s right to fire an officer who used his off hours to make and sell X-rated videotapes with police themes.

The unsigned opinion, which was issued without formal briefing or oral argument, was also an unmistakable rebuke to the 9th Circuit Court of Appeals, which had ruled in favor of the officer earlier this year.

The case involved a San Diego police officer who used a popular auction Web site, eBay, to sell sexually explicit videos. In the tapes, the officer appeared both in and out of a police uniform, though not one used by his department.

The Supreme Court found no merit in the appeals court’s ruling that the officer, identified in court papers by the pseudonym John Roe, was entitled to special legal protection because his videos amounted to speech on a matter of “public concern.”

“This is not a close case,” the justices wrote. “We have little difficulty in concluding that the city was not barred from terminating Roe.”

While the appeals court found that the officer’s off-duty conduct had no direct connection to his position on the police force, the Supreme Court sharply disagreed. “Far from confining his activities to speech unrelated to his employment, Roe took deliberate steps to link his videos and other wares to his police work, all in a way injurious to his employer,” the court said.

The high court took particular note of one video, which was commissioned by an undercover internal-affairs investigator. It showed the officer issuing a citation and then, after undoing his uniform and masturbating, revoking the ticket.

“The debased parody of an officer performing indecent acts while in the course of official duties brought the mission of the employer and the professionalism of its officers into serious disrepute,” the justices wrote.

In an interview, an attorney for the city of San Diego, Penny Castleman, said the Supreme Court’s decision was a relief, not only to her city but to local governments across the country.

Ms. Castleman, who wrote the city’s petition to the Supreme Court, said local officials feared they had lost all ability to regulate the conduct of their staff while off the clock. “When the 9th Circuit opinion came out, I got phone calls from all over,” she said. “It could not be the standard that government employers could just have no control over, especially, law enforcement officers, in their off-duty time,” she said.

The ex-officer’s lawyer, Michael Baranic, said he was disappointed with the court’s ruling.

“I believe it’s contrary to their prior decisions,” he said in an interview yesterday.

Mr. Baranic said the ruling would invite government employers to micromanage their employees’ conduct while away from the job. “It sure opens up the door,” he said.

A professor who teaches police tactics at New York University, Jerome Skolnick, said the high court’s decision was driven by common sense.

“I’m not surprised at all. What was surprising was the 9th Circuit’s decision,” he said. “Were the police department to permit this, they’d be a laughingstock. If the Supreme Court was to permit this, they would also be held in low regard, certainly in the police world.”

A law professor at the University of California, Eugene Volokh, said the justices were sending a clear message to lower courts to respect government employers when they assert that an employee’s speech or actions are disruptive.

“They’re asking courts to take really seriously claims of interference,” he said.

Mr. Volokh termed the Supreme Court’s opinion “a little conclusory,” however, on the question of precisely what trouble was caused by the officer’s action. “There’s no connection to the San Diego Police Department in the video,” he said.

While online, the officer apparently never used his real name. Instead, he used a handle, “Code3stud,” which is a reference to an urgent police call.

The 9th Circuit’s opinion pointed out that there is no evidence that the city ever received a complaint from the public about the officer’s videos or that anyone outside the force ever figured out that “Code3stud” was a member of the force. Investigators in the department became suspicious after seeing an out-of-date San Diego police uniform for sale on eBay. They later signed onto an adults-only section of the Web site. There they recognized the officer from the photos “Code3stud” had posted.

Mr. Volokh said the extent to which the investigators had to go undercuts the city government’s suggestion that the conduct posed some threat to the department’s reputation. “I doubt that a typical person would blame the police department,” he said.

Soon after the officer filed suit over his firing, a district court judge, Judith Keep, threw out the legal claim. She said that, under a 1968 Supreme Court decision, the officer could prevail only if his videos involved a “matter of public concern.”

The 9th Circuit determined that the videos met that standard. The appeals court said that the key question was whether the videos were sent to the public, not whether they involved is sues in public debate, and that the officer’s suit deserved a full hearing, in which a judge would balance the officer’s First Amendment rights against the city’s interest in maintaining an orderly police department.

The 9th Circuit ruling overturned by the Supreme Court yesterday was written by Judge Raymond Fisher, who was joined by Judge Dorothy Nelson. Judge Kim Wardlaw dissented forcefully, on grounds similar to those set forth yesterday by the justices.

In its decision, the Supreme Court made clear that no detailed balancing is needed when the speech in question is not tied to a broader public discussion. “Public concern is something that is a subject of legitimate news interest,” the court wrote.

That rationale would appear to suggest that a police officer, or any government employee, could be fired for starring in X-rated videos that did not make any reference to his or her employment. The court stopped short of resolving that issue, however. “That’s a closer question,” Mr. Skolnick said. “You probably wouldn’t get a 9-0 decision.”

Ms. Castleman said she reads the Supreme Court’s ruling to mean that governments are free to take action against employees who engage in immoral behavior on or off the job. “I don’t think it matters if you’re doing it in uniform or out of uniform or whether you’re a cop or not,” she said. “You’ve got to be able to regulate that.”

Mr. Baranic said his client got a job working for the federal government soon after he was fired from the police force.

The attorney declined to say for which agency the ex-officer now works.