Shereker Wilkins died on her ninth birthday last month, killed by a stray bullet fired from the street as she sat in her Milwaukee apartment, combing her mother's hair. In New Orleans that week, Dorothy Mae Gourrier, 59, was killed on her way to a doctor's appointment. A would-be robber opened fire on her car, shattering the windshield and wounding her in the shoulder and chest.

For the past several years, law enforcement authorities have blamed drug trafficking - especially of cocaine and its derivative crack - for the surge in urban crime. But this year, a new and in some ways more alarming trend is developing: The drug epidemic in many American cities shows signs of abating, but the culture of violence that accompanies it is thriving as never before. After increasing steadily for three years, the number of homicides in 1990 is breaking records in urban areas nationwide.Cocaine and crack may have encouraged and financed the violence as traffickers brought large numbers of top-of-the-line weapons to replace the cheap, poorly made "Saturday night specials" and rubber-band-powered zip guns of the past. But the ethic of firepower has taken on a life of its own. Guns have become part of the urban landscape, injecting an extra element of fear into everyday life.

"There's a viciousness out there on the street with people with weapons," said the police superintendent of New Orleans, Warren G. Woodfork. "They don't care if they live or die, it seems, or if you live or die."

In interviews in 16 cities across the United States, Washington Post reporters and special correspondents spoke to law officers, community activists, criminologists, young people and residents of some of the nation's toughest neighborhoods.

In 15 of the cities, murder rates have increased over those of 1989: Boston by 45 percent; Denver, 29 percent; Chicago, Dallas and New Orleans, more than 20 percent each; Los Angeles, 16 percent; and New York, 11 percent. In Washington, which led the nation in number of homicides per capita last year, the rate is slightly ahead of last year's record pace.

Those interviewed mentioned drugs, poverty, television violence, social tension and hopelessness - root causes of violence that have afflicted the inner cities for generations. But they also spoke of guns, gangs and a new street ethic that in many cases almost requires young men to commit murder to prove manhood.

"As kids under 18 got involved in drug dealing, they got armed," said Lawrence W. Sherman, president of the Crime Control Institute, a Washington-based think tank. "Even if drug dealing declines, they still have the guns. Once the guns have been stockpiled, you can expect they will be used in all kinds of disputes."

Gang members, said Dan Cabrera, special senior agent for the Los Angeles office of the Bureau of Alcohol, Tobacco and Firearms, "rule by fear - fear of dying is a strong motivator. If you're trying to get respect and you've killed three or four people, people are going to jump when you give an order."

This year, the new ethic of violence has meant banner headlines for a flood of seemingly senseless, gruesome crimes.

Even more disturbing for law enforcement, however, has been the increasing use of firearms as the preferred tool for settling disputes from domestic quarrels to schoolyard slights.

In a South Philadelphia apartment this month, Tuan Anh Nguyen, 18, was fatally shot in the chest, arm and stomach when a dance-party quarrel erupted in gunfire. In Brooklyn last month, barber Ferdinand Augustin died when a would-be customer shot him in the head with a .25-caliber pistol after Augustin refused to give him a haircut.

"I see a lot of violence at the slightest provocation - `you stepped on my sneakers, you said something about my mother,' " said Mel Grizer, executive director of the United Community Center in the East New York section of Brooklyn. "There's a lot of kids getting killed over girlfriends."

There is little argument that drug trafficking has played a crucial role in spawning the rise of violent crime - cocaine in the early 1980s and crack in the past five years.

"In the 1960s and '70s, it was heroin, which just makes people lie down and go to sleep," said Richard Bank, a 17-year career public defender in the Philadelphia court system. "Today, the heroin is cocaine, which makes people very excited and nervous. They're much more dangerous."

But most available indicators suggest that, over the past year, even hard-core cocaine and crack abuse has begun to decline in many parts of the country. The number of people being treated for cocaine-related hospital emergencies peaked nationwide at 11,285 in mid-1989. During the first three months of this year, the figure had dropped to 8,135, lowest since 1987.

Statistics available in many other cities have shown slight downward trends, or at least a leveling-off from previous increases in drug use. By contrast, however, the Senate Judiciary Committee projected in August that 23,220 people would be murdered nationally this year, making 1990 the bloodiest on record, although the per-capita homicide rate would still be slightly below that of 1980, when 23,040 people were murdered.

"Police are telling us there is more violence that doesn't involve drugs," said Stephen E. Rickman, director of statistical analysis for the office of Criminal Justice Plans and Analysis here. "It's kind of a spillover effect. It's become an acceptable way of settling disputes."

Still, many law enforcement officers do not believe that drug violence is declining. They have noticed, and the Drug Enforcement Administration reported this summer, that cocaine prices have risen over the last year while street purity of the drug has declined, indicating that cocaine is becoming more difficult to obtain.

No one interviewed disputed the proliferation of guns on America's streets and the willingness of people to use them. Today's street weapon is more sophisticated, more expensive and more deadly than ever.

"They're not using `Saturday night specials' anymore," said Capt. Donald Curole, chief of homicide for the New Orleans Police Department. "It's MAC-10s and 9mm" semi-automatic pistols. "Ten years ago, a victim would have one or two gunshot wounds at the most. Now you're seeing multiple gunshot wounds-10-15 in one victim. There's a tremendous amount of overkill."

Besides more and better guns, today's violence has other prominent characteristics. One is race. In Boston, the proportion of black murder victims rose from 41 percent in 1973 to 67 percent this year, and this year Boston police reported that 78 percent of murder suspects are black.

In New Orleans, 203 of 229 murder victims through Sept. 30 this year were black, 187 of the black victims were male and 266 of 284 murder suspects were black. "Mostly, it is black males who are dying," said New Orleans police spokeswoman Carmine Menchel. "We're seeing black males killing black males."

A second characteristic of murder in the 1990s is that it involves young people more than ever. A study by Washington's Center to Prevent Handgun Violence found that the number of youths murdered by firearms nearly doubled between 1984 and 1990, from 962 to 1,897.

Yet while the rate of arrests of teen-agers for murder also doubled, arrests for other crimes - including rape and robbery - did not increase significantly, the Crime Control Institute study showed. "It's not like kids are going out and attacking more people like you and me," said the Institute's Sherman. "They are shooting each other."

Carl Bell, a University of Illinois psychiatrist, recently completed a study for Chicago's Mental Health Council that found that 74 percent of 1,000 South Side and Southwest Side children had witnessed a killing, shooting or robbery. Among students from South Side high-crime areas, 24 percent had seen someone killed.

For small children, coping with the violence has become a traumatic burden. "I stay in the house almost all the time," said Malika Mitchell, 10, who lives in Brooklyn's Brownsville section and was interviewed at an East New York community center. Just two or three years ago, she said, "I would go outside and ride my bike. Now it just sits in the corner."

Jeffrey Jones, 10, had another solution: "I want to move to Florida, to Orlando. Every time I visit, when you're watching the news, you don't hear things like, `He got shot, he's going to jail. He's on America's Most Wanted.' "