A Prince George's County youth who claimed he was under the influence of drugs when he tied a plastic trash bag around the head of a 6-year-old girl was convicted by a county Circuit Court jury last night of second-degree murder in her death.

The youth, Gary Wellford Brown, 16, testified in his own defense Monday that he had smoked several marijuana cigarettes sprinkled with the hallucinogen PCP just before he placed the bag over the head of Angela Spriggs and tied it around her neck while they were playing hide-and-seek.

Angela, a pupil at Beacon Heights Elementary School, was found dead of suffocation Jan. 23 in a field near her Landover home. A green plastic trash bag was tied over her head, her hands were tied and her mouth was taped shut.

Prosecutors had argued that the slaying was premeditated and that Brown should be convicted of murder in the first degree, while Brown's attorney, David Deacon, contended his client was incapable of premeditation because his use of drugs before the girl's death had left him unable to control his behavior. Deacon argued that if Brown was responsible for the girl's death, she died by accident, and that at most he was guilty of manslaughter.

Court officials defined second-degree murder as killing with malice, but not with premeditation. Brown, who will be sentenced next month, could receive a maximum term of 30 years in prison. The jury deliberated about 4 hours before reaching its verdict shortly before 11 o'clock last night.

Brown, a dropout from Walker Mill Junior High School who had been friendly with the girl and her family, was arrested and charged with her slaying the day she was found. Police began questioning him immediately after her parents reported her missing since he was the last person seen with her, according to court testimony.

In his summation to the jury, assistant state's attorney Stephen Orenstein argued that physical evidence showed the killing had been premeditated. White string was wrapped around Angela'shands about 20 times, and the bag around her neck was tightly tied with string and rubber bands, he said.

Deacon contended, however, that Brown and the girl were good friends and that the youth never meant to hurt her. "When there is no motive, it is very hard to show planning," he said.

In a statement Brown gave to police after his arrest that was later entered in evidence, the youth wrote: "I am very sorry for doing this . . . Angie was like a sister to me . . . "