TO THOSE WHO say you can't stop people in big cities from killing each other, there's a three-word rebuttal: New York City.

The remarkable drop in New York's murder rate that began in the 1990s has continued while other cities - like Philadelphia - have suffered reversals in their crime-fighting gains.

New York's murder rate is now less than one-fourth of Philadelphia's, and Gotham will likely end the year with fewer than 500 killings, its lowest level in 44 years. In 1990, New York had more than 2,200 murders.

It's often forgotten that New York's war on crime began in the early 1990s with a major tax boost to fund a massive increase in the police force.

But most criminologists say New York used its expanded force well, with smart, aggressive, data-driven police work and a focus on smaller crimes that created a sense of order and swept thousands of guns from the street.

The change was led by former commissioner William Bratton. He's now police chief in Los Angeles, where homicides have declined substantially since he was hired in 2002.

"You can't compare us to New York City," said Philadelphia Police Commissioner Sylvester Johnson, who argued that New York is far more affluent than Philadelphia, "and they have much better gun laws there."

Philadelphia's poverty rate was only 1.8 percent higher than New York's in the 2000 census, though estimates suggest New York's poverty rate has fallen slightly since then while Philadelphia's has grown.

Frank Zimring, author of "The Great American Crime Decline," said no changes in New York's economy or demographics explain its remarkable drop in violent crime, so "you conclude it's the police by the process of elimination."

Temple criminologist Ralph Taylor said New York top cop Tom Kelly "is an incredible commissioner who's done a lot of smart, innovative things."

It's particularly impressive that New York's murder rate has continued to fall since 2000, even though the size of the city's police force has declined by about 10 percent, from 40,000 officers to about 36,000.

Taylor said he thinks one factor in New York's continued crime drop is the level of immigrants in its population.

"New York is much more tied to international commerce, and it would have lost population in the last census if not for immigration," Taylor said. "There's data going back to the 1930s showing less crime among the foreign-born." *