District of Columbia Police Chief Cathy Lanier knows a lot of the anti–Wall Street protesters camped out in Freedom Plaza, a sliver of a park located between Capitol Hill and the White House. Protests are a way of life in the nation’s capital, and Lanier works hard to build a measure of trust with the demonstrators, walking among them and handing out her cellphone number so anybody can reach her.

“I don’t care who you are,” she says with a laugh. “You’re not going to find me in the office.”

Lanier is the District’s first female police chief, and at nearly six feet tall with blonde hair and a ready smile, she has been a very visible presence throughout the city. Since she was appointed chief in 2006, the city’s crime rate has fallen and is on track to have fewer than 100 homicides for the first time since the 1950s.

She is confident she has the Occupy Wall Street (OWS) protest under control for now, but watching what’s happening in New York and elsewhere, she is preparing herself, and the force that she leads, for something she fears could become massive and potentially violent.

“Any spark could escalate this movement,” she says. “If it happened anywhere, it could happen here—no matter how good a relationship we have with our protesters and our demonstrators to keep violence down.”

The Supreme Court police over the weekend arrested 19 OWS protesters, including Princeton Prof. Cornel West, for refusing to vacate the court’s steps. So far at least, the D.C. police have not tussled with the demonstrators.

Lanier says she understands their goal is to disrupt traffic and inconvenience people, and she noted that a recent march on Pennsylvania Avenue during rush hour did not make them any friends among commuters trying to get home to Virginia. When an ambulance had to get through, the police were able to move the protesters aside.

In lower Manhattan, when the police threatened to evict protesters from Zuccotti Park, claiming they needed to clean the area, demonstrators amassed in a show of strength that forced the authorities to back down.

“One more swell like that could spark a movement that could get out of control very quickly,” Lanier told attendees at a reception honoring her by the nonprofit INFO/Public Policy Roundtable on Monday evening. “Over the next several months, we could be facing some very major violent protests here.”

Lanier says she is “fascinated by the psychology of crowds,” and how quickly the dynamics can turn toward violence. “You have to prepare for the worst,” she says. When asked how she does that, she says, “I haven’t stopped my civil-disobedience training. You can never let your guard down.”

The District of Columbia has not had violent demonstrations with property damage since 2004, when people moved through smashing windows in Adams-Morgan, a hip downtown neighborhood, to protest George W. Bush’s inauguration.

Lanier recalled the spontaneous demonstrations that erupted to celebrate Barack Obama’s inauguration in January 2009. Almost 2 million people descended on the District that day, and as Lanier watched thousands walking across the bridge from Virginia, she knew she needed every one of the 5,000 additional police borrowed from jurisdictions all over the country.

“We can pull them together quickly,” she says, while noting that “if this protest sparks off in many different cities at the same time, major cities across the country will be very busy.” That is the nightmare scenario that Lanier knows all the good will she has built may not be able to avert.