A 14-year-old District youth was arrested yesterday and charged with first-degree murder while armed, the culmination of an intensive investigation into the slaying of a lawyer on Capitol Hill two weeks ago, D.C. police said.

The juvenile, who police sources said has a criminal record, was arrested at his home in the Potomac Gardens housing project of Southeast Washington, a few blocks from where Kenneth W. Goshorn, 46, was shot while sitting in his car.

The arrest came after a week of concentrated police activity in the neighborhood by detectives from the homicide unit and the 1st District, as well as members of the police Rapid Deployment Unit, a special force formed in October to combat violent crime.

The investigation was designed to develop information on a case that officials said lacked solid leads, and it hinged on getting tips from criminals known to police who would object to constant police presence.

"We knew this was the way to break the case, by putting pressure on the area," said a police source who attributed the case to solid legwork by investigators. "If you put enough pressure on them, they're going to cough it up."

Information from the street produced the name of a juvenile who allegedly was present when Goshorn was shot Jan. 3. Detectives questioned the youth, and he reportedly supplied the name of the alleged killer, the police source said.

Police said the two juveniles were standing together near 11th Street and Pennsylvania Avenue SE, where Goshorn's red and white Mustang convertible was stopped for a traffic light about 6 p.m. At first, investigators believed the shooting occurred after Goshorn argued with the gunman, who may have fired in retaliation.

But detectives have all but abandoned that theory because several witnesses said there was no dispute. That left investigators with no motive for the slaying, and even after yesterday's arrest it is unclear what prompted the crime.

The two youths have told detectives that the gun went off accidentally while they were standing on Pennsylvania Avenue. But witnesses' descriptions of the gunman running away from Goshorn's car and shooting behind him cast doubt on that explanation.

"With all the witnesses we have, we know that's not the case," the police official said.

Under District law, juveniles 15 and younger cannot be tried as adults. Those who are convicted remain in the juvenile corrections system until they are 18, at which time their cases are reviewed by a judge.

Goshorn's death prompted a strong response from friends, many of them lawyers who closely followed the police investigation.

A memorial service days after the shooting drew several hundred people, and a candlelight vigil at the site of the shooting was attended by Mayor Sharon Pratt Dixon.

The homicide unit, as part of a plan designed to crack cases that have few leads and receive media attention, made Goshorn's slaying a priority.

That prompted at least one complaint from a police investigator, who said the killing of Goshorn was receiving more attention than other cases, several police officials said. The controversy had racial overtones because Goshorn is white and most of the city's homicide victims are black.

Dixon made it clear that all homicide cases should be treated equally. Police officials, some embarrassed by the episode and others saying it was blown out of context, quickly moved to try to quell the controversy by agreeing with Dixon.

Yesterday, Police Chief Isaac Fulwood Jr. called Dixon to announce the arrest.

A spokesman for the mayor, while reaffirming her earlier position, said she "was very pleased with the response."

Homicide officials, still sensitive about the incident, declined to discuss it yesterday.

Other police officials outside the unit said recently that it is not unusual to assign more detectives to a case in which there are few leads.

The Rapid Deployment Unit was formed to help the homicide squad, and it has been credited with solving several homicide cases.