Baltimore Mayor Martin O'Malley lost his third police commissioner in five years yesterday, another setback both for a city beset by violence and for the political aspirations of its telegenic young mayor.

O'Malley fired Kevin Clark yesterday, saying a controversy over domestic abuse allegations against the chief proved too great a diversion from the efforts to halt crime.

Maj. Leonard Hamm was named interim chief.

The shake-up could prove tough for O'Malley, who first ran for office in 1999 on a pledge to bring order to a city with seemingly intractable social woes -- and to a police department dealing with one of the most violent urban centers in the country.

Five years later, having just won reelection with 87 percent of the vote, O'Malley remains a rising star in national Democratic circles and is poised to contend for his party's gubernatorial nomination in 2006. But at home, he faces persistent instability at the top of his police department and a stubborn crime rate.

Although violent crime is down by some measures, O'Malley has fallen well short of his original pledge to cut the annual homicide rate from more than 300 to 175 during his first term. There were 271 homicides in Baltimore last year, and there have been 249 since January, putting the city on pace to surpass last year's figure.

O'Malley's political rivals are already preparing to use his record on crime against him.

"What we're seeing is the mayor has failed to reach the most important goal he established for himself," Paul E. Schurick, communications director for Gov. Robert L. Ehrlich Jr. (R), said yesterday.

Should O'Malley run for governor, political analysts said the mayor might confront a problem that has hobbled other popular big-city mayors as they try to reach the next rung on the political ladder. It's been more than a century since a New York City mayor became governor. And Los Angeles mayors Tom Bradley and Richard Riordan both failed in bids to reach the California state house.

"Big cities are difficult to manage," said Donald Norris, a professor of public policy at the University of Maryland at Baltimore County. "I can foresee his opponents in the primary and general election running ads and sending out fliers showing various problems in Baltimore and asking, 'So you want this guy to run your state?' "

O'Malley has never openly discussed his plans for 2006, but his advisers said yesterday that the mayor has no qualms about the prospect of running on his record in Baltimore.

By their count, violent crime overall is down by 40 percent in the city. And the failure to reach the mayor's goals to reduce homicides by almost half, they said, is not something to be ashamed of.

"His style of management is to set aggressive goals," said Steve Kearney, O'Malley's communications director. "It's the way you motivate the city, mobilize government agencies and employees, and it's how you let the public know what you expect."

O'Malley's aides also defended the move to fire Clark, who had been cleared of wrongdoing after a domestic dispute in May with his fiancee but who faced new questions about records that surfaced last week. They showed that he had dealt with similar allegations when he served with the New York Police Department.

Clark replaced Edward T. Norris, who left the commissioner's post in late 2002 to become state police superintendent. Norris was later convicted of fraud for misusing Baltimore police funds. O'Malley's first chief, Ronald L. Daniels, resigned after 57 days on the job.

Kearney said it matters less to the mayor how many commissioners he hires than the results they achieve for the city. "If it takes one police commissioner to do it or 10, if crime is reduced . . . that is what he will be judged on," he said.

But to state Republican leaders, the reshuffling in Baltimore's police department and its number of homicides invite criticism of O'Malley's performance.

State GOP Chairman John Kane said this about Clark's dismissal yesterday: "Regrettably, the third time was not a charm for this mayor. The people aren't being served. This guy goes out and plays in his band while Rome is burning." O'Malley occasionally plays in a rock band.

Some of O'Malley's allies contended that it is unfair to judge him on Baltimore's crime statistics and noted that William Donald Schaefer (D) was elected governor even though crime was a nagging problem during his four terms as Baltimore's mayor.

Still, Temple University criminology professor Ralph Taylor said it is not unreasonable to hold mayors accountable to a degree for the crime rate in their cities, even though a range of factors contributes to the rise and fall of such statistics.

"There are a lot of stubborn factors, and the mayor can't be expected to change all of them," Taylor said. "But there are plenty of examples of mayors that have spearheaded initiatives that have had an impact on crime, and any mayor can reasonably be judged on their ability to do that."

Leonard Hamm was named nterim commissioner. He's the fifth person to run the agency under O'Malley. The distraction of abuse allegations led to the firing of Kevin Clark.