Kelly Knerr seemed lonely and vulnerable as she paced a short stretch of busy Brownsville Road trolling for men. The traffic whizzed by in the dark, making her head spin.

She looked shabby -- no hot pants or halter top, just the worn jeans and jacket of a drug-addicted prostitute looking to turn a fast trick for drugs.

Ms. Knerr peered into passing vehicles and eyed men walking by, sizing them up. It was only 8 p.m. on a recent Friday night outside the bustling Foodland parking lot in Carrick, but she was sure she could find business, even under the glare of the fast-food restaurant across the street.

It took all of 27 minutes.

A man pulled his pickup truck into the lot and parked right behind her. He was a typical john. Wife. Two grown children. Full-time job as a factory worker. He stared. She pointed to herself, as if to ask, "Are you looking at me?" He nodded. The game was on.

After two minutes of haggling over the price of oral sex, Ms. Knerr closed the deal. Then she gave a prearranged signal. Seven pairs of eyes watching from three unmarked vehicles spotted it and moved in. Undercover police officers arrested the man for patronizing a prostitute. One of Ms. Knerr's partners swooped in and spirited her away.

The man's red-light hooker, it turned out, was really a lady in blue.

For Officer Knerr, a five-year veteran, the operation was her eighth time masquerading as a hooker in what police call a reverse prostitution sting.

During the past two months, vice detectives have been under orders from top brass to ramp up stings and arrest customers.

Citizens' complaints about men and women having sex in alleys, prostitutes sitting on their stoops, and people tossing used condoms on or near their property are driving the police response. And police said heroin -- which in recent months has been seized about eight times as much as crack cocaine in the city -- is driving prostitution. Women become hooked and sell their bodies to earn enough for their next fix.

"They want to get enough to get high and they're done for the day," narcotics and vice Lt. William Mathias said.

Pittsburghers have complained about several spots, drawing police to the Hill District, Lawrenceville, the North Side and several southern neighborhoods, including Carrick.

During the stings, a female officer poses as a prostitute and wanders street corners looking for men. When the deal is struck, the decoy's backup makes the arrest.

Police view reverse stings as a way to balance out arrests of prostitutes. It's only fair, they say, to arrest the men, too. And from an economic viewpoint, going after the johns is a demand-side strategy.

"It's good to keep the johns on their toes," Lt. Mathias said. "If you don't have johns, you don't have a prostitution problem."

Through October, police made 259 prostitution-related arrests -- 32 of them johns -- compared with 432 all of last year and 531 in 2001.

Although enforcement is down, that does not reflect the extent of the problem. Deputy Chief William Mullen noted that in recent years the number of police officers has dropped, the force lost a vice sergeant's position, and the personnel shortage has led to a reshuffling of priorities. A decline in arrests does not necessarily mean a drop in the crime.

In fact, prostitution is cropping up in some unaccustomed places.

"You could see they're moving into Carrick, where we've never had a problem before," Deputy Chief Mullen said.

Decoys dress for success

During her day job coordinating police manpower for special events, Officer Knerr, 30, looks crisp and polished in her blue uniform and shiny badge.

But when her shift ended that night, she left for a few hours and then returned to police headquarters on the North Side dressed for undercover work. Her long hair, usually worn up while on duty, was down in a ponytail. She wore jeans, sneakers and a light jacket. Her gun and badge were hidden under her shirt.

Female decoys are told not to look too glamorous. Many already know as much from dealing with prostitutes as patrol officers. A woman who seems too clean will likely tip her hand and repel men rather than reel them in.

"You just wear the bummiest jeans you have. Always an oversize sweatshirt, your dirtiest tennis shoes," Officer Knerr said.

Officer Chrissy Gasiorowski, who works with Officer Knerr in uniform, also has done decoy work. When she goes out on a sting, she doesn't wash her hair, skips the makeup and wears her husband's coat.

Decoy work is not for every female officer. Many don't like it. But for those willing to try it -- often early in their careers -- working undercover can enhance a resume and give an officer a leg up on becoming a detective.

Decoys get some ribbing from the guys, but male detectives recognize the guts it takes to work undercover and respect the women who do it and produce arrests.

The work can be unpleasant. Men say all sorts of lewd things. Women have to go with the flow.

"It's very degrading to talk like that and look like that," Officer Gasiorowski said. "Some of them want to grab you, to watch you. 'Show me your chest.' And we'll come back with, 'It's going to cost you five bucks.' You're suddenly just a piece of meat."

That's what bothers her husband, Pittsburgh police burglary Sgt. Kevin Gasiorowski.

"You do get upset because it is your wife and you have these guys making these lewd propositions to her, but then you realize it's part of the job," Sgt. Gasiorowski said. "We actually laugh about a lot of the stuff."

There is always the danger that the decoy will be assaulted, which is why so many backup officers staff a sting. Pittsburgh police do not wire the women because of strict state wiretap laws, meaning they can't hear the conversation between the officer and the john. And some of the male customers carry guns.

"Prostitutes get killed all over this country," noted Lt. Mathias.

'I tell her to be very careful'

Around 7:15 p.m. Nov. 4, six narcotics and vice detectives, Officer Knerr and Sgt. Douglas Epler sat around a table in the squad's conference room for a quick briefing. They discussed tactics, locations and signals before heading to Carrick.

Officer Knerr was a bit nervous. She had never worked on Brownsville Road before. But she had the benefit of past experience -- and a mother, Elaine Knerr, who is a 19-year veteran of the force and has run prostitution stings out of the East Liberty station.

"I just tell her to be very careful," Elaine Knerr said.

Once in the neighborhood, the group met with a uniformed officer whose job was to hide her marked car and transport the johns to jail. Then they dropped Officer Knerr off and got into position. It was 8 p.m.

"OK, guys, our friend's out on the beat, copy," crackled the radio.

At 8:11, a guy in a car stopped to talk to Officer Knerr but quickly drove off. He returned a few minutes later.

"He's building up his courage," one of the detectives said over the radio.

"He's real squeamish," Sgt. Epler replied as he watched. "Chicken. Do it!"

No luck. The car took off. It turned out he wanted to see Officer Knerr naked, but left when she asked for $20. Officer Knerr was offended. "You know what kills me?" she said later, "On the North Side they pay $20."

It was only a temporary setback. The factory worker rolled up moments later. He was the first of three johns to be busted by 10 p.m. The others were a construction worker and a roofer, but police also have arrested white-collar customers, including a computer analyst and a professor.

After the arrest, Sgt. Epler zoomed up. Officer Knerr got in and described what happened.

"I said, 'You looking to party? He said, 'Yeah, I'm looking to party. He said, 'How do I know you're not a cop?' He said, 'How you gonna prove it to me?'"

She told him to come to the back of the parking lot with her and she would show him. The deal: oral sex for $10.

"There's some cheap bastards out here," Sgt. Epler said with a laugh. A short time later, he let Officer Knerr out to set up for the next bust.

"All right, honey, have fun at work," he teased. "See ya."

"Don't stay up too late," she shot back.

City is less harsh than some

Some communities advocate public humiliation of johns as a way to stop their behavior. Denver is a prime example. The city's Web site posts names and pictures of johns. Their faces can also be seen on "Johns TV" on the city's cable channel.

In some cases, johns' cars are impounded for two months, meaning that wives will almost certainly find out about their husbands' indiscretions.

"It's ugly, isn't it?" said Denver police Lt. Donna Starr-Gimeno, who runs the force's public nuisance abatement unit. "Momma wants to get the car out and she wants to know what the hell's going on. We've had some knock-down, drag-out fights right here in my office."

Pittsburgh has no punishment so harsh. Here, second-time offenders might get jail time. But those arrested for the first time will likely end up at "johns school," a program launched by police Sgt. Lavonnie Bickerstaff in 1999 after surveying residents of the city's Bluff neighborhood. People there complained of prostitution. But it wasn't only the women who bothered them.

"They didn't want the men to just get off scot free," Sgt. Bickerstaff said.

Johns sit through six hours of presentations. They are lectured by vice detectives, prosecutors and former prostitutes. They learn about health risks and the impact of their crime on a neighborhood. And then they are told they can have their records expunged. So far, 419 men have gone to class.

Officer Knerr has no sympathy for the johns. She feels badly, though, for their families.

"I think it's terrible that they're out with these heroin addicts, IV drug users," she said. "They don't know what they have, they don't know what they're taking home to their wives."