Two prostitutes whose bodies were found in South Arlington last weekend died from asphyxiation, police say.

They were the sixth and seventh prostitutes killed in the metropolitan area in the past 13 months. Four of the others were shot to death, and the fifth was bludgeoned.

The body of Sandra Rene Johnson, 20, was found Sunday morning inside the South Glebe Road apartment building where she lived. On Saturday, the partly clothed body of Sherry K. Larman, 26, who lived in Maryland, was found atop a four-story garage on South Highland Street near Columbia Pike.

Police sources said both women had been arrested on prostitution charges in the District. Authorities declined to give details of their investigation, or to say whether they believe the weekend killings are linked to each other or to the five earlier deaths.

Arlington County police spokesman Michael Rocconi said his department is coordinating its efforts with other police agencies.

"We're cooperating with police in Alexandria and in the District of Columbia in our investigations," he said.

Police sources in Alexandria and in Arlington said that so far, the only common element is that the victim in each of the seven cases is a prostitute.

Also yesterday, Arlington police identified Reginald Keith Veney, 32, as the man who shot and killed his estranged girlfriend, Geraldine Whitley, 22, as she waited at a South Arlington bus stop Monday evening. Veney then turned his shotgun on himself, in the second murder-suicide in the county this year.