A noted criminologist who studied Baltimore's murder culture for 18 months has concluded that understanding why gunmen pull the trigger is crucial to curtailing shootings that plague many city neighborhoods.

Officials plan to provide details of the study today and make it the crux of the city's most ambitious plan yet to end gunfire that has claimed several thousand lives in the past decade and stained Baltimore as one of the nation's deadliest urban centers.

David Kennedy, a Harvard University professor, said local law enforcement officials have operated under a false perception that there is no way to understand why the violence occurs, and therefore no way to prevent it.

"That's not right, even in the hardest-hit areas," Kennedy said. "At the street level, there is a logic and a history to almost everything that goes on. It's not immune to understanding, and is not immune from prevention."

Kennedy said that most city violence, particularly homicides, comes from a "small, identifiable group of folks who are well-known to the criminal justice system and who are responsible for a great majority of the violence."

The announcement of what is called Operation Safe Neighborhoods comes after a monthlong delay prompted by concerns that a series of breakdowns in the city's court system would prevent agencies from working together, which is critical to the program's success. Some suspects have been freed because of the court crisis.

Local and federal officials said yesterday that those concerns are over. Kennedy dismissed the problems as typical politicking that has also occurred in Boston. Baltimore police have begun implementing the plan by targeting a group of violent offenders on the city's east side.

The project is based on Operation Cease Fire, created by Kennedy and credited with lowering street violence in Boston in the mid-1990s. It calls for an unprecedented attack by employees of more than a dozen agencies, from social workers to probation officers, to target a core group of offenders and put them out of business.

It is a daunting task in Baltimore, where more than 300 people have been killed annually and thousands more shot each year since 1989. The city was ranked fourth-deadliest per capita last year.

"Our goal is particularly lofty," said Hathaway C. Ferebee, director of the city's Safe and Sound program.

Kennedy and Assistant State's Attorney Kim Morton outlined the plan yesterday and described 18 months of studying 303 homicides from 1997, dissecting more than 300 drug groups and identifying up to 4,000 "impact players" who are disproportionately responsible for shootings and other violent crime in the city.

Kennedy's conclusion that a small number of people are responsible for the bulk of violence has been known by police for years. For the most part, they have blamed the problem on revolving-door justice that sets repeat offenders free.

But Kennedy said the problem is more complicated. He said that while most homicide suspects and victims have lengthy arrest records, so do thousands of others. Simply targeting people with rap sheets won't help, he said.

Kennedy's team studied 303 homicides and 210 murder suspects from 1997. Nearly three-quarters of the victims and 90 percent of the suspects had prior arrest records.

Each of the suspects had been arrested an average of 9.6 times before being charged in a killing; each of the victims had been arrested an average of 8.5 times before being slain.

"It validates what the police commissioner has said for a long period of time -- that violent crime begets violent crime," said Baltimore police spokesman Robert W. Weinhold Jr.

Kennedy also found that nearly half of the suspects were involved with a drug group and 60 percent of the slayings occurred in or near a street drug market.

But only one-fifth of the homicides were directly related to the sale of drugs or battles over turf, Kennedy said. Though most of the slayings involved people connected with the drug trade, the source of the disputes were arguments over women or linked to men who make careers of robbing drug dealers.

And, Kennedy said, there is a method to the killers' madness. Police officers on the beat often know the true motives, as do relatives, friends and neighbors.

But too often, he said, police reports end with the cryptic, and often misleading, "No motive, no suspect" -- many times because the stories are not easily substantiated.

That has led to a common misperception that the violence is random. Neighborhood residents have good reason to be concerned, Kennedy said, but the true danger is limited to the estimated 4,000 core criminals. "They are scared, and they are scared of each other," he said.

Kennedy acknowledged that Boston, a smaller, wealthier city than Baltimore, had an easier crime problem to solve than Baltimore's.

The professor said Baltimore has more open-air drug markets than he has seen in five major cities he has studied, including Boston and Minneapolis, and he found that in many cases, demand is so high that rival dealers share small geographic boundaries.

Baltimore, with 159 killings this year, is on a pace for its lowest murder count in a decade. Last year at this time, 197 people had been slain. As of yesterday, the city had gone seven days without a homicide; the last one occurred Aug. 8.

But 41 people have been shot since then, including 10 in two separate shootings on Sunday. "Way too many," muttered Maj. Jeffrey R. Rosen, who commands the homicide unit, as he slowly counted the list of victims. "Nothing to be happy about here."

Morton, who has been working with Kennedy, was at first skeptical of the study. A Baltimore native, she had grown up with what seemed like unrelenting violence, and said she believed there was no discernible reason for the killings -- the city simply was a violent place.

Kennedy said his study proves otherwise. His plan is to identify drug groups who call attention to themselves by shooting people. Then, he wants police to target the individuals who are leaders or gunmen.

Not only will they be arrested, but they will be selected for special attention by every facet of law enforcement. If they are on probation, it will be revoked. If they are out on bail, they will go back to jail to await trial. Outstanding warrants will be served.

Kennedy said these are simple questions that had never before been asked by officials who often worked in a vacuum. He said once individuals are identified, arresting and prosecuting them -- especially for violation of probation -- is relatively easy.

The next step is for law enforcement to have face-to-face meetings with members of drug groups, to warn them that they will be arrested if the violence doesn't stop. Kennedy said that tools to go after such people, such as probation violations, do not get used as often as they should.

"Every one of these [4,000] core individuals know they are vulnerable," Kennedy said. "They are just not used to their vulnerability being exploited."