The first rape in Reston in about six months occurred in July near a shopping center. Then, a few weeks later, another woman was raped not far from the site of the first attack.

Since then, the rape total has risen to seven, with the victims including a 15-year-old girl and a 70-year-old woman. With no suspects in sight, many residents of Reston, the Fairfax County planned community built in part as a haven from the evils of urban living, are uneasy, to say the least.

"We have this beautiful community, a place ideal for living, and yet we have to be afraid," said a mother of three, who asked not to be named. "It makes you angry and sorry and sad at the same time that we have to harbor this fear."

That fear already has imposed changes on Reston life styles, residents say. Women now walk in pairs, for instance, and parents chauffeur their children door-to-door. Locks are routinely checked at night where before there was little concern. The Fairfax County police SWAT team has been dispatched to the community. And a total of $7,000 in reward money has been offered by residents.

"We know that, as the population of an area grows more and more, you have statistically a higher chance of coming up with this kind of s.o.b. invading your lives," said Reston Community Association president Harry Mastakos. "So you just don't go forth with the same kind of naivete."

Mastakos says the community is fighting back, something that residents say is not surprising, considering what they say is the spirit of Reston, 30 miles from Washington where committees and carpools and fathers who volunteer to coach soccer are the norm.

In one example of such spirit, Philip Landis, owner of a gas and oil exploration company and a longtime resident, donated $5,000 to the reward fund. "I did it to make a positive statement," Landis said. "I wanted to do something to show this guy that we citizens are actively trying to create an environment where people will think twice about bringing harm here."

In addition, there have been neighborhood watches, say residents.

Yet, though there is fear, said Mastakos, residents have maintained a sense of community.

"Even with the troubles," he said, "we know Reston has been and always will be a very well-planned community with caring people dedicated to the idea that concern for each other can be a driving motive of life."

"Reston is viewed as an ideal and model community, and it's my view that it's just that," said Fairfax Police Chief Col. Carroll Buracker. "I like Reston. The problem I see is occasionally when you have a model community, something can happen and it gets a lot more attention. They're just not used to it."

In fact, police say, Fairfax County has the lowest rate of violent crime of any county in the Washington metropolitan area, and Reston's rate is even lower than that of the county as a whole. In 1981, for instance, Fairfax County reported slightly more than 174 crimes per 100,000 people (compared with Montgomery County's 295 per 100,000 and the District's 2,278 per 100,000). And in 1982, when the major crime in Fairfax County decreased by 16.5 percent, crime in Reston dropped by 20 percent.

Buracker also pointed out that seven rapes in Reston, the only seven since January, are not a large number, statistically. In l981 there were four, in 1980, 11, and in 1979, eight.

"The data doesn't show that Reston should be a place where residents are worried about their safety," said Buracker. "Last year, there were only three robberies in Reston where a gun was used. In a community of 65,000, that's incredible."

Part of the problem, Buracker said, is that Reston's wooded trails -- there are about 40 miles of them winding through the 70-square-mile community -- are prime spots for potential rape attacks.

To combat that disadvantage, said Capt. Andrew Page, commander of the police public affairs division, police have assigned a large number of officers, including foot patrolmen, undercover officers and their 16-man SWAT team, to investigate the rapes.

Buracker said all of the rapes have occurred in a two-square-mile area near the Hunters Woods Village Center. Four of the women were attacked on wooded trails. Two women were raped in their homes.

Whether one man is responsible for the rapes is unclear, police said. They did say that the rapes all have involved someone who is said to be tall and muscular. In all cases, the rapes have occurred after dark. In one case the assailant was armed with a knife, according to police reports.

Buracker also said he has been in touch with other jurisdictions, particularly Aspen Hill in Montgomery County, where there have been 16 sexual assaults in the past 18 months, but that "it's hard to say if there is any connection with the Aspen Hill rapes because the circumstances in most rapes are similar."

Mastakos, of the Reston Community Association, which donated $1,000 of the reward money, said citizens are pleased with the action county police have taken.

"They are concerned about the community and about community relations, and are competent and dedicated in the same way we are to ensuring that Reston stays a good place to live."

Still, the specter of a rapist stalking Reston is unsettling to most residents.

"I was kind of worried about putting up $5,000 toward that reward," said Landis. "I was afraid the guy would come after me."