A 21-year-old South Arlington man was arrested last night and charged with homicide in the death of a prostitute found slain in the county two weeks ago. Police said he also is under investigation in the slaying of a second prostitute in Arlington.

The arrest was the first since police said they were investigating the possibility of a serial killer or killers in the deaths of seven prostitutes found dead in the District and Northern Virginia since April 1989.

The suspect was identified as Chander Matta. Law enforcement sources said he lives on South Oakland Street in Arlington, not far from where the two women's bodies were found May 26 and 27 -- the sixth and seventh prostitutes found slain.

Arlington County police said Matta was charged in the death of Sherry K. Larman, 26, who was found May 26 on the top level of a four-story parking garage in the 900 block of South Highland Street.

Arlington police said Matta also is being investigated in connection with the death of Sandra Rene Johnson, 20, whose body was found a day later.

Johnson's body was found in the Country Club Towers apartments at 2400 S. Glebe Rd., where she lived. The site is less than two miles from where Larman's body was found.

Investigative sources said both of the women apparently had been smothered with plastic bags.

Both Larman and Johnson worked along L Street between 12th and 15th streets in Northwest Washington in an area known as "the stroll."

The deaths of the two women touched off an intensive investigation by Arlington police and were followed by a meeting among police in several jurisdictions.

Arlington police said last night that Matta's arrest resulted from an investigation conducted with Alexandria and D.C. police and the FBI.

"We all worked together," said a D.C. homicide sergeant.

There was no immediate indication of what led investigators to Matta, who authorities said was arrested at 9:30 p.m.

One investigative source said the arrest was made by Alexandria police and that it apparently followed a period of questioning.

In addition, a source said police yesterday searched the house on South Oakland Street where the suspect lives with his parents.

Several people living in Matta's neighborhood were contacted last night, but said they knew nothing about him.

Authorities indicated last night that Matta also will be investigated in connection with the death of a girl whose body was found in Alexandria within five days of the Arlington incidents.

An Alexandria police spokesman said that the 16-year-old found dead near Dawes Avenue also had been asphyxiated.

He said autopsy results on that girl are pending.

Matta is to be arraigned today in Arlington General District Court.

After the deaths of Larman and Johnson, police said that the five other prostitutes who had been killed since April 1989 also had worked along the area known as "the stroll" and had blond or light-colored hair.

But in addition to these similarities, investigators said there were sharp differences among the victims.

After determining that Larman and Johnson were asphyxiated, police theorized that those deaths were related.

Two of the other women were shot in the head, two were shot in the chest and one died from a blow to the head.

Three of the victims were found in the District, and District police said ballistics evidence shows that at least two of the three probably were shot with the same gun.

Police have said that the evidence and the circumstances point in many directions, and while some investigators raised the possibility of a serial killer or killers, sources have said that as many as seven assailants might have been involved.