A 6-year-old Northeast Washington boy was shot in the head and killed in his bed early yesterday after two men who had left a party at the boy's home returned and started shooting. The bizarre and unexplained incident was the sixth fatal shooting here in little more than 48 hours.

The weekend killings, which brought to 12 the number of unsolved slayings here this year, came as the police added seven members to the hard-pressed homicide unit, bringing its strength to 53, possibly the highest total ever.

According to police, about 10 people had been attending a party early yesterday at Angela Copeland's home at 1367 Florida Ave. NE and some were still there at 3:30 a.m. when two men who had been there previously smashed open the door. The men began shooting, firing at least eight shots, police said.

One shot entered the skull of Copeland's son, Marquis, as he lay in bed. The boy was taken to Children's Hospital and placed on life-support systems. He was pronounced dead at 10 a.m.

The boy was a first-grade student at Miner Elementary School. He was an enthusiastic artist and investigators arriving at the house yesterday found one of his drawings stuck to the battered door.

Another person in the apartment was hit five times in the flurry of gun-fire, for which police said they have learned no motive.

Everyone else scattered, diving behind furniture and into closets. The wounded victim, Gregory Byrd, 20, of 5011 F St. SE, was reported in serious condition last night at the Washington Hospital Center.

Police said they arrested Roderick D. Robinson, 19, of 1225 I St. NE, who also has used the last name of Gross. He was charged with assault with intent to kill in the shooting of the boy. Police said the charge was filed before the boy was pronounced dead. Another man is still being sought in the incident.

Victims of the previous shootings, which occurred Saturday and Sunday, were listed as Roger A. Garrido, 24; Charles White; William Walker; William Henry Johnson and Barry Lee Gilcrist. Garrido, Walker and Gilcrist were killed during robberies or suspected robberies. White was shot allegedly after an argument with an off-duty police officer. Johnson was found in a car, shot several times. Details of his death were not immediately known.