Kathryn Strand, a graduate student at the University of Pennsylvania, used to walk home from campus to her Rittenhouse Square area apartment at all hours.

Not anymore. Strand and many other students and young working women in her neighborhood have been living more cautious, fearful lives since police linked six sexual attacks to a serial rapist who has been stalking young women around the square for more than two years.

"I used to walk home at 2, 3 a.m.," Strand said. "Now, I take the Penn shuttle," which drops her at her front door.

The fear in Rittenhouse Square started in May 1998 when Shannon Schieber, a 1992 graduate of Montgomery County's Bethesda-Chevy Chase High School, was found strangled in her second-floor apartment. Her neighbors had called police, reporting screams from Schieber's apartment in the early morning hours. Officers knocked on her door, got no answer and left.

Her parents, who live in Chevy Chase, think that Schieber, who was a graduate student at the Wharton School, was in her apartment with her slayer when officers knocked on her door. They declined to comment for this story. But they have filed a lawsuit against the city and the two officers, alleging that the officers not only failed to help Schieber but also may have put her in greater danger by refusing to break in when they got no response.

"Had they gone in the night of Shannon's murder, they maybe could have saved her, and it's fairly clear they could have caught him that night," said Marc Fleischaker, attorney for the Schiebers.

At the time Schieber was killed, police believed the attack was an isolated crime. But earlier this year, police linked DNA evidence from the Schieber case to three sexual attacks that occurred in the neighborhood in the summer of 1997--before her death. Then the fear for some in Rittenhouse Square became all-encompassing, as it became clear that there was a sexual predator preying on young women in the neighborhood. The most recent assault, which took place in August, was linked almost immediately to the others, according to Capt. Stephen Glenn of the Philadelphia police homicide division.

Police are investigating whether other sexual assaults in the neighborhood can be linked to the same assailant.

The police department's sex crimes unit has come under fire recently, after an investigation by the Philadelphia Inquirer found that, for years, detectives sometimes downgraded sex offenses to make crime statistics look better and didn't always thoroughly investigate sexual assaults.

"It appears there were several attacks prior to Schieber's murder," said Carol E. Tracy, executive director of the Women's Law Project. "One wonders had [the previous sexual attacks] been investigated thoroughly, would that have given police the reason they needed to knock in her door that night?"

Strand, 23, fits the profile of the rapist's victims--typically young, white women, often students, who live alone in this charming community of brownstones surrounding tony Rittenhouse Square, an oasis of green in the midst of one of the city's most upscale neighborhoods.

She avoids going places alone. She makes fellow graduate student Maria Elena Garcia-Prieto, who lives several blocks from the shuttle stop, call when she gets home to let Strand know she's arrived safely.

"These things happen everywhere," Strand said. But having it so near "makes me hesitant."

These days, while mothers watch over young children playing in Rittenhouse Square's dry fountain and weekday workers enjoy an Indian summer lunch on a park bench, posters with a composite sketch of the rapist are everywhere in sight--plastered in the windows of the IHOP restaurant, a shoe store, the local Laundromat and the kiosk in the center of Rittenhouse Square. The grim black-and-white drawing--white male, dark hair, slim build, 5-foot-10--is as well known in this community as any celebrity photo, but the description is vague: He looks like everybody and nobody.

Peggy Guerin, who lives and works in the neighborhood, said her husband was waiting for her after work one recent evening, and a police officer was eyeing him carefully and jotting down notes. Almost any man who meets the general description is fair game for suspicion.

For now, many women are taking steps to better protect themselves. In recent weeks, Rittenhouse Hardware has been selling at least a dozen cans of Mace each week; usually it sells about one a month. The store also has been selling lots of window pins and bars to residents seeking to beef up security. A local women's college has brought in self-defense instructors.

At Chaucer's Tabard Inn, fewer women are venturing out after dark for the Monday night ladies' special offering half-price drinks. And at Rittenhouse Square Fitness Club, attendance at evening aerobics classes has dropped by almost half since publicity of the serial rapist spread this fall, while more women are coming to the gym before work and at lunchtime.

Elizabeth Leonard, 23, a manager at the fitness club, still walks the three blocks to her home when she gets off work at 11 p.m., but now she makes sure to walk by apartment buildings staffed by doormen--and she carries pepper spray. She asked the police to do a safety survey on her apartment, and got the landlord to fix the window locks in her fourth-floor unit. With two dogs, she feels pretty safe, but she isn't taking anything for granted.

"I have thought about getting a gun," she said. "It's frightening to know someone is out there, maybe watching you."