A six month undercover investigation by an Arlington County vice officer has resulted in the arrest of 40 persons on narcotics charges during the past week, Arlington County Police reported yesterday.

Police said warrants for possession and sale of drugs including marijuana, heroin, cocaine, amphetamines, PCP and LSD have been issued for 49 persons, most of them Arlington residents. However, Commonwealth's Attorney William S. Burroughts said the arrests were largely unrelated.

"There is no evidence of a large scale drung ring," he said. "These people are for the most part unconnected individuals or groups of two or three."

According to Burroughs 18 of those charged are juveniles and several are students at Wakefield High School. "We have no reasons to believe any were below high school age," he said.

Police said they began to make the arrests Dec. 2 shortly after an Arlington County grand jury returned indietments against the group. Neither police spokesman nor Burroughs said they knew the street value of the majority of charges were related to the possession or sale of PCP, LSD and cocaine.

Police said the arrests are continuing and should be completed by early next week. Police declined to release the names of those charged until all have been arrested.