Detective Gerald Robertson has seen many prostitutes in his time, and this one, like most, was obviously fluent in the second language of 14th Street: lies.

He first had noticed her on Thomas Circle about midnight last Jan. 5. She had the right strut, the right style--that black cowboy hat, leather boots, the white fur jacket.

Robertson drove closer. Beneath a street light, he could see her features: Her brash demeanor was that of a hardened prostitute. But her face, visible beneath a curly wig, was that of a child.

He called her to the car. Her hands were shaking. Pouting, she plunked herself in the back seat.

She identified herself as "Michelle" and said she was 23.

Robertson marveled at the brazen response.

He could tell the girl was young. But he did not learn until later that she was just 13, one of the youngest prostitutes the D.C. police had ever encountered.

"I just came out," she told him. "That's all I want to do, make one trick and go into the house and pay the rent."

He listened as she rattled on about her wig being real hair and the purple spot under her left eye being mascara. She lied about her parents being dead, about which school she attended. She lied about her address and about not having a pimp. She was intractable. Over the next four hours, she gave Robertson five different ages and three different names.

When he challenged her, she said, "Sir, I don't lie."

Robertson sighed. He wanted to avoid arresting her for prostitution, giving her a criminal record that would put her on a treadmill she might never get off. For the time being, that would mean allowing her to walk away. But he would be back.

"You're out here dressed as Annie Oakley. I've got to find out who you are," he told her as she got out of the car. "A little thing like you might get stomped on."

Robertson wrapped himself in his leather jacket and for the rest of the night stalked the girl, listened to her lies, contacted her sister, and searched for her pimp. He worked with a rare intensity, for there was a child on the streets.

If removing child prostitutes from 14th Street were as simple as finding them, Robertson's job might be a lot more satisfying.

Robertson can understand giving a criminal record to a seasoned prostitute. It's a nightly ritual between consenting adults--the hundreds of women who work 14th Street, and the 20 officers who cruise it to catch them.

But Robertson, who has an 11-year-old daughter, believes that young girls are not criminals. They are victims of crime: abuse and neglect. Instead of arresting these children, he takes them into "protective" custody, talks to them, tries to learn who is exploiting them, and sends them to court as legally ungovernable.

"If my daughter was out there and I couldn't get to her, I'd want somebody to at least have the initiative to try to do something about it," says Robertson.

Yet the D.C. Corporation Counsel's office says that, unless he is searching for a missing person, Robertson cannot arbitrarily remove children from 14th Street if he is unwilling to issue criminal prostitution charges. The city prosecutor invariably dismisses such cases outright, allowing the girls to go free.

"The law is very clear," says Nan R. Huhn, chief of the Corporation Counsel's juvenile division. "You can't just see a girl standing on 14th Street, say, 'She looks young,' and pick her up. You can't exercise police power because you're concerned about someone. We're not in a situation where the police are the kids' parents."

Robertson says he is not sure laws to protect children actually achieve that purpose. "I assume they do have their so-called 'rights,' " Robertson says. "However do they have a right as an 11-, 14-, or 15-year-old, to be out there working as a prostitute, endangering their health and well-being? We have the right to prevent it . . . . Somewhere the line has to be drawn."

There isn't always a lot of satisfaction from working on the 3rd District prostitution squad. A dozen times a night, a thousand times a year, undercover officers disguise themselves as businessmen or conventioneers and drive their unmarked cars along the "Street of Dreams," waiting for a proposition, arresting an unsuspecting prostitute. Female officers dress as prostitutes and when men proposition them, they give a routine signal to backup officers that they have enough evidence to arrest the john.

In the end, judges usually order the johns to write essays as punishment and the prostitutes generally are fined and sentenced to a few hours or, at most, a night in jail.

"I dislike locking up the women--to me it's a moral issue," says Winston Starke, an officer in the 3-D prostitution squad. "I like going out there and arresting the bad guys--the robbers, the rapists."

The officers seek other rewards. Richard Skirchak, a 12-year veteran, says he looks forward to the extra overtime pay for court appearances that accompany most arrests. "If I had to go to court for nothing," he says, "there'd be a lot less arrests made."

Robertson long ago concluded that adult prostitution arrests are made so the police can prove to the public that something is being done about the problem. When he sees the signal that a john has been caught, he gleefully drives up, singing, "Turn out the lights, the party's over."

He would rather concentrate on cases of child prostitution. In 1976, he helped launch the police department's first juvenile prostitution unit. To him the "bad guys" are the pimps who exploit the girls. His greatest challenge is persuading juveniles to get off 14th Street for good.

"If we turn around just one or two a year, if we do nothing else, I feel like we've accomplished something," says Robertson's partner, George Johnson.

As far as Robertson is concerned, that kind of persuasion should not require sending in the undercover officer just to prove she is a criminal.

"Allow her to commit a crime, just so we can lock her up and get her into the system? That's sick," Robertson says.

"We should deal with these people the very day we see them. No matter how you look at it the kid is a victim. . . . We're taking this child out of an environment that, whether she created it or someone created it for her, is not in her best interest . . . . In my mind, she isn't intelligent enough to know what her best interests are . . . . I've never had any qualms about snatching a kid off the street."

Learning about a 13-year-old prostitute is more than just arresting and re-arresting the ladies of the evening. It means hours of waiting and sitting and checking and going into hotels where she might have stayed, and when the manager says, "Most of the girls we had are gone now," it means asking again, giving a description, having someone suddenly remember, and getting a room number.

It means checking with the more seasoned prostitutes who had seen her on the sidewalk and hoping--correctly, as it turned out in this case--that professional jealousy might prompt them to supply Robertson with information about their pint-sized competition.

Robertson likes to tell the prostitutes he encounters: "I'm the best pimp you'll ever have. You don't have to pay me anything."

Despite a life of lies, these women will be honest if it is in their interest. For example, Robertson routinely hears if one of their customers is carrying a gun or if they have been assaulted.

And when a group of Michigan pimps muscled its way into Washington last October and placed a half-dozen new prostitutes on Thomas Circle, infuriating the local streetwalkers (there were threats of shootings and the turf battle became known as the "October War"), the word was passed to the police. One raid later, the Michigan pimps left town.

Robertson takes down in notebooks much of what he hears and shares it with the other detectives. If three women give the same phony address, it might mean they work for the same pimp. It is a cast of characters that Robertson and all the detectives know well.

There are veteran prostitutes, like the portly woman who stands at Corcoran and 14th, who have grown to recognize the undercover officers and successfully avoid arrest. And there are others, such as the glittery Hannah Thompson who has been arrested 50 times.

Robertson banters with the women, collecting bits of gossip and the nightly chatter of the street. He also examines letters and diaries confiscated by police. One prostitute, in a letter from her pimp, was told: "You have pledged yourself to me for a lifetime. You do not think, for when you think you will make a mistake. I am the thinker and you are the performer. There is no limit as to how far we can go together . . . . Some day, you may own your very own real estate."

The prostitute-pimp relationship often can be violent. One night last January, detective Johnson and Sgt. Al Simmers found a woman in the emergency room at a Washington hospital. She was being treated for a concussion and head injuries inflicted by her pimp after she tried to leave him. "I'm afraid he'll try to kill me, or really beat me bad," she told them. "He's known on the stroll as 'Crazy T' and, believe me, he fits the bill."

Johnson and Simmers sent the complaint to a judge in Prince George's County and the pimp, who had been free on probation, was sent back to jail.

The prostitution squad tries to break the bond between pimp and prostitute, but such victories are rare. With juveniles, it is even more difficult.

"That's the biggest problem," says officer Patrick Dennis. "Their parents never took the time to say, 'I love you.' . . . Some pimp out there did ." Dennis says he feels a particular anguish: A distant relative of his once was a prostitute; another was a pimp.

After Robertson's initial meeting with the young prostitute on Jan. 5, he decided to contact some veteran streetwalkers he knew. By the evening's end, he had learned a lot about the girl.

She had been seen on the "Boulevard," as the prostitutes call 14th Street, for just a few nights. She was born in 1968, as her birth certificate later showed. She had dropped out of a local junior high school. Her pimp, a man called Shawn, had recruited her at a McDonald's ("Mac's House of Beef," the police called it). She was staying in a hotel just west of Thomas Circle.

Robertson and Simmers parked outside the hotel and waited for her.

"Speak of the devil," Robertson said as she reappeared. He called out her real name.

She turned around immediately. But when she saw Robertson, she denied that was her name.

"You ain't going back," Robertson said.

With the girl pleading not to be locked up, Robertson escorted her to his car.

"Been working the street long?" he asked on the way to the police department's youth division.

"No."

"How many tricks?"

"Eight."

"What do you charge?"

"$25 and up."

"Where do you turn your tricks?"

"We usually do it in a car."

When they arrived, Robertson took her to a paneled room. He closed the door. He told her: "I don't like the idea of you going out there working as a prostitute. We have two options: jail, or your mamma . . . . "

"I'm sick of being in the house," she told him.

"You're stupid being out there, giving your money to some dumb-dumb."

"I spend my money on me," she protested.

They talked for hours. She rolled her chair back and forth, muttering impatiently as Robertson asked questions. She would answer, and Robertson would interrupt periodically, saying, "You're lying to me, darling" or "Girlfriend, I told you not to lie."

Robertson checked police records and discovered that she was a chronic runaway: 11 times from home; 43 days from school last semester. He learned something else: This child already had a pending criminal charge--burglary.

"This must be my lucky night," she said. "Ain't this a bitch?"

"Let's get to the part where you decided to be a whore," Robertson said. "Whose idea was it?"

"It was my idea."

"I hope you enjoy jail--Whose idea?"

" . . . Shawn's. He wanted to be my pimp. He liked me very much . . . . "

"When did you turn your first trick?"

"Saturday . . . . "

"Who took you out and told you how?"

"I had a girlfriend . . . . She showed me a couple of places. She pointed out the cops . . . . I be smart about it. Every time I see them I go the other direction."

"You didn't move fast enough tonight."

She later said, "I'm not out there every night. That don't make you a prostitute. I only do this when I want to."

"What will Mamma think when she hears you're a whore?" Robertson said. He asked about her designer jeans.

"I bought them with my godmother's money."

Robertson rolled his eyes. "What would she think if she knew these jeans were on a prostitute?"

Robertson asked why she was a prostitute, and she said it was the money. "There's things that I want, and see. When I see things I like I can't get it 'cause I ask my mother--I can't even ask her to give me $3."

At about 3 a.m., Robertson decided that his rehabilitation project was going nowhere. He had hoped for more with her because she was so young and presumably still impressionable. He realized he was trying to counter an attitude in hours that had taken 13 years to develop.

At one point, Robertson tried to reach her family. He spoke with her sister who explained that their mother felt the girl was out of control.

"Mamma says she cannot handle you no more," Robertson said. "A judge is going to have to handle you. You'll be working on my streets no more."

As she was led away, she asked: "Are prisoners allowed soda?"

"Your little girl's on 14th Street again," another officer told Robertson the following night. He made a few calls and learned the city prosecutor had dismissed his "child in need of supervision" case against her. She had been released that morning.

Robertson went to 14th Street and again picked her up. The next morning, her case again was dropped, but a judge agreed to hold her pending her burglary trial in juvenile court. On Feb. 9, she pleaded guilty and until sentencing was sent to Cedar Knoll, the city's facility for delinquent children.

In May, she escaped from Cedar Knoll, and was recaptured a month later.

Last week, on the day of her sentencing, the prosecutor told the judge she had again escaped--and is still missing.

If she goes back to 14th Street, Robertson says he will be waiting: "Unless I get an order from someone higher up, telling me that I can't pick up these children, I will continue."