A Reston woman who was sexually assaulted inside her apartment Tuesday night may have been the sixth victim of a man who has committed a series of similar attacks mainly in north Reston, Fairfax County police said yesterday.

In four earlier break-ins since September 1998--one involving two victims--a short, thin man wearing a ski mask and wielding a handgun surprised women in their homes. Sometimes, the man pried open a door or window, and sometimes he slipped in through an unlocked door, police said.

There were no obvious clues as to how the man in Tuesday night's attack broke into the ground-floor apartment, police spokeswoman Jayne Woolf said.

The victim, a 28-year-old woman, had just entered her apartment in the 1500 block of Cameron Crescent Drive when the masked gunman grabbed her from behind and sexually assaulted her after a struggle. The woman was not seriously beaten or robbed, Woolf said.

The woman described the suspect as white, possibly Hispanic, about 5 feet 5 inches tall and thinly built, with a long-sleeved plaid shirt and gray khaki pants, according to authorities. Police did not have a description of the mask worn in Tuesday's attack, but in the similar cases, the assailant wore either a black or white ski mask.

The victim called police immediately after the 10 p.m. attack, Woolf said. Detectives, crime scene technicians and uniformed officers returned to the area again yesterday morning, canvassing residents and searching for evidence in the daylight, Woolf said.

The first attack in the series occurred Sept. 20, 1998. Two women on Forest Edge Drive took out their garbage, and when they returned to their town house, they were confronted by an armed man in a black ski mask, according to authorities. A police affidavit said that the man spoke with both victims at length, asking for marijuana and alcohol, and that he had a Spanish accent.

In the second assault, on Oct. 28, the assailant blindfolded his 28-year-old victim inside her Rosedown Drive house. The third incident occurred Feb. 19 in an apartment in the 1700 block of Lake Shore Crest Drive. The 25-year-old woman told police the gunman was waiting for her when she entered her second-floor apartment just northwest of the Reston Town Center.

After the third assault, Fairfax detectives formed a task force to focus on the "Reston rapist" and consulted with the FBI for help in developing possible suspect characteristics. Officers also distributed fliers in the neighborhood near the Town Center.

In the fourth attack, June 6, a 23-year-old woman was confronted in her second-floor apartment in the 1700 block of Jonathan Way by a man with a white mask and a handgun. She was ordered to disrobe and was assaulted. That attack was at least the second in which the man is believed to have entered a second-story residence, police said.