An Alexandria grand jury indicted 27 Northern Virginians yesterday in connection with charges that they sold cocaine, hashish, LSD and marijuana to an undercover narcotics investigator in the city's West End.

Alexandria police official Vicki Will said a lone undercover officer made a total of 66 drug purchases from 45 persons in a nine-week period ending May 10. The probe ended abruptly that day after the officer was recognized as a policeman in a bar int he 5200 block of Duke Street, Will said.

The alleged dealers, most of whom police said were between 18 and 22 years old, were described by law-enforcement officials as small-time sellers who operated independently. The youngest of those charged was a 16-year-old Alexandria girl, who allegedly sold the undercover officer a gram of cocaine for $100, Will said.

"All [of the Alexandria buys] went down west of Quaker Lane, mainly in the evening hours in parking lots," according to Alexandria vice Sgt. Lennie George. He said one of the initial buys led the undercover officer to the Alexandria campus of Northern Virginia Community College "and then it started snowballing."

Eight or nine of the purchases took place in the parking lot or inside buildings at the school, George said, adding that police did not consider the NVCC campus "a drug haven."

Another 16 purchases occurred in Arlington and Fairfax counties and have been turned over to authorities there, police said. They said most of the sales involved quantities ranging from a gram to an ounce of cocaine, and from an ounce to a quarter-pound of marijuana.

The largest dollar value was an ounce of cocaine worth $2,200 allegedly sold by two sisters, according to Sgt. George.

In a separate development, a federal grant jury in Alexandria indicted a District of Columbia woman yesterday on charges that she attempted to smuggle 264 pills called "purples" and "tans" into the Lorton Reformatory last February.

Loretta Y. Sweet was charged with smuggling and possession with intent to distribute the drugs, which when cooked and injected are commonly referred to as the "poor man's heroin," federal prosecutor Anthony Epstein said.

Authorities said Sweet was arrested in a trailer at the reformatory's main gate. She is scheduled to be arraigned in federal court on Friday.