The partly clothed body of a woman was found behind an office complex in Alexandria last night. It was the third such discovery in Northern Virginia in five days.

Two women who were found dead in South Arlington last weekend had been asphyxiated; they were identified by sources as prostitutes who worked in the District and as the sixth and seventh prostitutes to be found dead in the District and Northern Virginia since April 1989.

It was not clear whether the death of the woman whose body was found last night was connected with the slayings of the two women, who were found Saturday and Sunday less than three miles away.

Alexandria police did not release the woman's identity and would not comment on the cause of death. They said the dead woman was white, as were the women found dead over the weekend.

The body was found about 6 p.m. in a grassy area behind the Seminary Professional Village, an office development in the 5200 block of Dawes Avenue in the city's West End, police said. They said the discovery was made by a groundskeeper for the office complex.

About 9 a.m. Saturday, the partly clothed body of Sherry K. Larman, 26, who lived in Maryland, was found atop a four-story parking garage on South Highland Street near Columbia Pike in Arlington.

About 5:30 the next morning, the body of Sandra Rene Johnson, 20, was found in the South Glebe Road apartment building where she lived. Police sources said both women had been arrested on prostitution charges in the District.

Arlington police said early this week that they were cooperating with police in the District of Columbia and Alexandria in their investigation of the two weekend killings.