Fairfax County police officials said yesterday they are ending one of their most intensive and costly investigations in recent years -- their inquiry into rapes in the Reston area -- after the indictment of a 24-year-old man on a rape charge.

Roland V. Thompson, who was indicted by a county grand jury in connection with the Jan. 6 rape of a Vienna woman, was investigated by the police department in connection with eight other rapes, including several that alarmed the Reston community late last year, said Police Chief Carroll D. Buracker.

"As far as I'm concerned, those eight other cases are closed," the chief said in an interview.

Police had closed a portion of the Reston investigation earlier this year, after the arrest of another man on a separate rape charge. That charge later was dropped after a victim did not identify him in court as her assailant.

Thompson, who lived in the Reston and Baileys Crossroads areas, has been held in jail on traffic charges for almost two months while police continued their investigation of the eight other Fairfax rapes. Until yesterday police had not said publicly that they had a suspect in custody in any of those rapes.

Last fall's $1 million investigation into the Reston area rapes cost the police department an average of $250,000 a month in salaries and overtime alone for more than three months. More than 50 uniformed and plainclothes officers swarmed the wooded trails and winding streets in the Reston area where most of the assaults occurred. Detectives surveyed jogging paths through hidden cameras perched on nearby rooftops. They went undercover, renting a town house and using young female police officers as lures. They pulled records and ran checks on almost 300 known sex offenders throughout Northern Virginia.

Commonwealth's Attorney Robert F. Horan would not comment yesterday on the police statements about the eight other cases. "Any case we thought was provable in court, we brought to the grand jury."

Thompson also was indicted yesterday on two counts of breaking and entering in connection with the alleged rape and a count of burglary involving a house near the home of the alleged rape victim, Horan said.

Thompson has been held in jail since Jan. 28 on a series of traffic charges. His arrest occurred after the date that police said Thompson became a suspect in the rape case.

The rape charge was brought directly to the grand jury, eliminating the preliminary hearing, normally required after an arrest to determine whether there is enough evidence to bring a case before a grand jury.

Buracker said the usual arrest procedure was bypassed to "avoid that first step a preliminary hearing that sometimes airs evidence."

He said the technique is sometimes used in rape cases because "we don't think the victim should be put on the stand twice."

Police say the the 13 rapes that occurred in Reston, Herndon and other Fairfax communities during a seven-month period last year and early this year have been among the most baffling cases investigated by the department. In the nine cases where police believed there was one rapist and tagged the elusive subject as the "town house rapist," the evidence was particularly weak, police said.

After the first few attacks, Buracker said, police believed they were dealing with a "professional," a man who had been through the criminal justice system and knew how to "cover his tracks." He wore a ski mask and overpowered his victims in positions that would not allow them to see his features, the chief said. The rapist wore gloves and left virtually no physical evidence at the scene of the assaults, Buracker said.

Uniformed officers knocked on hundreds of doors in search of information. Undercover officers posing as joggers and bikers kept watchful eyes on the pathways. A "rag patrol" of officers dressed in shabby clothes loitered outside house garages and under street lights, trying to arouse the suspicions of neighbors, hoping people could provide some leads.

In addition to the uniformed and plainclothes officers that patrolled the streets and pathways of Reston, police went undercover renting a decoy house that matched the description of the town houses where the victims resided. It was selected for its sliding glass doors and its shadowy front yard.

For several weeks, police officer Suzanne Ricketts was assigned to live in the house and attempt to lure a suspect inside. A team of police officers occupied the second floor with microphone bugs and other surveillance equipment.

The decoy operation and the surveillance resulted in no arrests. The elaborate undercover operation was abandoned in early January.