When Boston's Mayor Thomas Menino swore in his city's 38th police commissioner in early February, he followed tradition. As bagpipes played, the new top cop took an oath to serve and received a gold-plated badge. Menino's choice for the job, however, was anything but traditional. For the first time in the department's 374-year history, the chief of the Boston Police Department is a woman. Menino says Kathleen O'Toole, 49, a former beat cop turned lawyer who ran her own international consulting firm, was the right person for the job. Gender, he says, "simply wasn't a factor."

O'Toole is the newest member of a growing sorority. In the past year women have been appointed top cop in three other cities: Detroit, Milwaukee and San Francisco. Criminal-justice scholars say these appointments could signal a major turning point in the struggle to break what has often seemed to be a bulletproof glass ceiling. In 1985, Penny Harrington became the first woman to run a major urban force when she was appointed chief in Portland, Ore. Few followed her path. Out of 18,000 departments in the country, only about 200--mostly small-town forces and campus police departments--are currently headed by women. But with women now running some of the biggest departments in the country, "it's reached critical mass," says Dorothy Schulz, a professor at John Jay College of Criminal Justice, who is writing a book about women chiefs.

That doesn't mean women are taking over policing. They now account for fewer than 15 percent of the 880,000 sworn law-enforcement officers in the country. But what is changing is the definition of a good cop. Big-city forces used to run on a paramilitary model, which relied on top-down leadership and prized physical training. These days, police officers are expected to be more service providers than soldiers. The emphasis on community policing encourages beat cops to focus on crime prevention and requires commanders to develop strong ties to neighborhood leaders. Education counts more too. In 1979, when O'Toole joined the Boston force, she was afraid to tell her bosses that she was in law school. "I didn't exactly hide it," she says, "but I didn't volunteer it either." But now, most departments require two years of college for beat cops and expect supervisors to have even more. That favors female recruits, who generally are more educated than their male counterparts.

The shift puts more women on the fast track to top jobs. Instead of giving the chief's badge to the "toughest guy in the valley," says Schulz, mayors are looking for sophisticated CEOs who can oversee large budgets, negotiate thorny management problems and set sound departmentwide policy. Modern chiefs are expected to be proficient at marketing and public relations too. "In many ways, the job has become more complex," says New York City Police Commissioner Ray Kelly, who himself recently appointed a woman chief to lead the 1,700 officers assigned to public housing. "It's become brains over brawn."

Which doesn't mean women chiefs aren't tough when they need to be. Detroit's Chief Ella Bully-Cummings, 46, sounded more like Dirty Harry in February when she announced new initiatives aimed at reducing a spiking homicide rate. "We know who you are," she warned. "We know where you are. And we're coming to get you." Acting San Francisco Police Chief Heather Fong has an advanced degree in social work, but it was her reputation as a stern disciplinarian that got her the job. She was brought in to clean house after the last police chief resigned in scandal. "There will always be people who say, 'She can't do it because she's not physically as strong'," says Fong. "But when there's [a] tough decision to be made, I can make it." That's the kind of strength a modern police force needs.