Mayor Bloomberg and the police commissioner, Raymond Kelly, have new data to back their long-standing boast that New York City is the safest big city in America.

For the 17th consecutive year, New York City in 2005 saw a decrease in violent crime, even as violent crime across the country was up, the FBI reported. Among the 25 largest cities, New York City ranks 25th in crime.

The city isn’t alone in diverging from the nationwide trend. Los Angeles, where a former New York Police Department commissioner, William Bratton, now runs the police, had decreases in violent crime in every category for 2005. (Because the Los Angeles Police Department changed the way it tracks crime, the percentage change wasn’t available, the FBI said.) Chicago, Dallas, and Miami also had decreases in violent crime.

“We’re 5,000 police officers below where we were in October of 2000 – so that’s a 12% cut in forces, and crime continues to go down,” Mr. Kelly said. “That doesn’t just happen. It happens as a result of a lot of hard work.”

The data released in the FBI’s preliminary annual Uniform Crime Report shows a 2.5% increase in violent crime among the 12,485 law enforcement agencies of which it keeps track. New York City had a 1.9% decrease in violent crime. The city’s crime rate changes for this year are less dramatic, with slight rises in the reports of murder and rape.

“It’s not about resources, it’s about strategies,” the director of the Center for Crime Control at John Jay College of Criminal Justice, David Kennedy, said.”In New York, L.A., and Chicago, there are three different but very deliberate and focused strategies being followed. There’s a reason that those cities are doing well.”

The FBI reports show that New York had a 1.4% increase in robberies in 2005. The police department’s chief spokesman, Paul Browne, said that hike had already been reduced using the Real Time Crime Center and a strategy of targeting high-crime areas with extra manpower, called Operation Impact. Robberies are down 3.7% this year, he said.

Cities like Boston and Memphis, with populations between 500,000 and 1 million, faced the greatest increase in violent crime last year, the FBI reports show.

“These are the cities that did a good job fighting crime in the 1990s,” the director of the Brudnick Center on Violence at Northeastern University, Jack Levin, said. To international acclaim, Boston police lowered the number of murders by teenagers to three from 39 between 1990 and 1993, but the rate is on the rise again after many community programs have been cut, he said.

“When they stopped supporting the programs and policies, their crime rate escalated again.” Mr. Levin said. “If we’re not careful, we’re going to be a national model for crime increases.”