On cold nights, when the city's most desperate prostitutes shiver in little more than their thigh-high vinyl boots, detectives on the street keep asking an essential question: "What's your date of birth?" or "How old are you?" and "No, really, how old are you?"

They know they're not being given correct answers.

The past year has been the most productive yet for the D.C. police department's newly revived prostitution unit. With more arrests, a record 923 as of late December, the four-year-old division learns more about the deep roots of the city's prostitution problem and the human wreckage permeating it.

"I think, sadly, this profession has always recruited juveniles and will continue to do so," said acting Sgt. Mark Gilkey, who heads the unit.

The arrest in November of a 12-year-old underscored the presence of juvenile prostitution in the District. But it was an unusual circumstance, sexual assault of the child while she was in a juvenile detention facility, that led to discovery of her age.

Many of the young male and female prostitutes are runaways. But their actual ages and names are rarely known to the District's legal system, making it difficult to track the rate of juvenile prostitution.

"I think that we can be 60 or 70 percent sure in some cases, just by looking at them, that some of these prostitutes are juveniles," Gilkey said. "But they don't have real IDs. They give fake names, and if they're young, they usually don't have a record. So we can never really find out if they're juveniles."

In some cases, with heavy makeup and skimpy clothes, appearances can be deceiving.

"Some of these girls just look so old," Lt. Diane Porter said. "From the rough life of the streets, you can never really tell how old they are."

Porter works day hours, taking complaints from citizens, listening to lieutenants in Patrol Service Areas and planning the next operation.

Based on complaint calls, the prostitution unit has launched an aggressive crackdown. It has a 99 percent success rate in getting courts to prosecute solicitation arrests.

But, "if we make 923 arrests and you can still walk outside your house and see a naked person on the street, we have more work to do," said Assistant Chief Brian K. Jordan.

Prostitution, he stressed, "is not only about a girl selling her body for sex. It's an organized crime, and we have a whole organization to investigate."

Increasingly, Jordan said, prostitutes use the Internet to advertise their services and cell phone numbers. But most aren't skilled computer programmers, and introduction of another party into the criminal enterprise gives detectives a new foothold.

"Now, we can include computer contractors in our investigations," Jordan said.

This kind of specialized work requires office time and limits late-night street raids for the 12-officer unit. Porter is trying to offset that by showing street officers how to operate independent of the unit and make arrests without a massive, undercover operation.

She is teaching beat cops that if they see a prostitute, they can ask her to leave the area. If the officers return and find here there, they can arrest her for failure to obey a police order. In some months this year, more than half of the unit's arrests were for that charge, according to a biannual report on the unit's activities.

The unit also investigates "bawdy houses," or bordellos, in otherwise quiet neighborhoods. For these cases, police have been helped by the best source possible -- the nosy neighbor.

At community meetings, Jordan encourages residents to become involved by calling police with license plate numbers and descriptions of suspects. He also urges them to write impact statements to judges, telling how prostitution affects their lives.

"Judges need to hear from people who say, 'I don't want my 16-year-old to see this' or 'I don't want a pimp out here, recruiting my 17-year-old daughter,' " he said.