SAN FRANCISCO – At age 22, Patricia West already has her small-business model fully launched. She’s done her market research, knows how to advertise online and has a competitive rate structure.

There’s just one problem: She works in the world’s oldest profession – prostitution – which is illegal.

In industry parlance, West is an “in-call sex worker.” Clients meet her in safe locations. Though this helps her avoid the violence and arrests that routinely come with working the streets, she’s always on guard for police stings on the Internet.

West wants that to change. She believes all sex workers, including exotic dancers and pornography stars, should be able to ply their trade free of the discrimination that comes with a criminal record.

She’s one of a number of sex workers waging a campaign to decriminalize prostitution here. They’re supporting Proposition K, which would shift the city’s focus from prosecuting prostitution to pursuing those who prey on sex workers and increasing public-health outreach. The goal, West says, is to reduce violence against women and improve the health of sex workers and their clients.

“It’s a morally based, antiquated law,” she said. “Decriminalize prostitution and you bring it out of the underground and off the black market. That way you can start organizing, clean up the dangerous elements. Sex workers want safe streets like everyone else.”

The battle over Proposition K is causing political rifts in this free-thinking city, which for years has wrestled with ways to effectively regulate its vibrant sex industry.

The measure is opposed by Mayor Gavin Newsom, District Attorney Kamala Harris and much of the business community, who say it will attract unwanted criminal elements to the city and hamper efforts to fight human trafficking.

But it also has powerful backers. Placed on the Nov. 4 ballot after receiving 12,000 petition signatures, Proposition K was recently endorsed by the Democratic County Central Committee. The measure is also supported by Jeffrey Klausner, director of sexually transmitted disease (STD) control and prevention for the city’s health department.

“When a female sex worker talks to her doctor, she’s often not forthcoming about her occupation for fear of arrest,” he said. “Doctors can’t give adequate care without knowing a patient’s occupational risks.”

Klausner hasn’t discussed his support for Proposition K with his bosses at the health department and acknowledges there may be a political price for his activism.

“But sometimes you just have to do the right thing,” he said.

The prostitution issue makes for uncomfortable politics. At least three supervisors voted to endorse the measure in the Central Committee tally, including Supervisor Jake McGoldrick. But asked about his support this week, his office declined to comment.

Former supervisor and Central Committee member Leslie Katz, a local attorney, said she also voted to endorse the measure.

“I walked into the meeting planning to vote no, but there was compelling testimony about STD statistics. A lot of people are engaged in prostitution without practicing safe sex,” she said. “But listen, this measure isn’t perfect. I’m still conflicted.”

Proposition K would ban San Francisco police from using any public resources to investigate or prosecute sex workers on prostitution charges. Critics say the law would attract pimps, human smugglers and others who profit from the sex trade.

“Prostitution is not a victimless crime,” said Harris. “It’s a crime that victimizes neighborhoods and plagues communities and compromises the quality of life of the people who live in those neighborhoods. This measure would prohibit us from putting public resources into helping those residents. And that’s not acceptable in this community.”

Proposition K isn’t the first attempt to decriminalize prostitution in the Bay Area. A similar effort by San Francisco sex workers two years ago failed to get enough signatures to be placed on the ballot. In 2004, Berkeley residents voted down a similar measure.

Terence Hallinan, San Francisco’s district attorney from 1995 to 2003, has long supported decriminalizing prostitution. He thinks Proposition K is a step in the right direction.

“I support the concept that prostitution is something that should be legalized but controlled. But how far citizens can go in telling police how they can spend their money is legally at issue,” Hallinan said.

If Proposition K were to pass, San Francisco would join 11 Nevada counties and the state of Rhode Island, which take a more liberal stance toward prostitution. Hallinan calls that progress.

“What it says is that San Francisco is strong on personal liberties; it’s not a kooky city at all,” said Hallinan, who after leaving public office has represented Mitchell Brothers, which owns sex clubs and theaters here. “People here are willing to say they need a change. They take positions that may seem a little out there, but in the end so often have turned out to be right.”

The city’s Erotic Service Provider’s Union, which spearheaded the initiative, argues that in countries such as the Netherlands, New Zealand and Thailand, where payment for sex is allowed, sex workers are more likely to use condoms and have lower rates of sexually transmitted infections, including HIV. But in San Francisco, prophylactics are often seized, backers of the measure say.

“Condoms are used by police and prosecutors as evidence of illegal activity, so sex workers are less likely to carry or use them,” Klausner said.

Critics say that argument is false.

“Condoms are evidence that prostitution is going on, but it’s not evidence against the sex worker themselves but the location of where the crime is committed,” said Tim Hettrich, who retired this year as a captain in the San Francisco Police Department’s vice and narcotics unit. “There’s no law against carrying a condom, or we’d be arresting 16-year-old boys all over town.”

Proposition K would force police to target people who prey physically on prostitutes – including thieves and customers.

Hettrich said those risks are overstated.

“Obviously, these people are victimized,” he said. “Customers say, I’m not going to pay this prostitute, I’m going to smack her.’ But I don’t think the magnitude of that violence is that high. And this new law would not stop the brothel owners and pimps from getting violent, it would help them. It’ll make it harder for police to zero in on their work.”

No proposal along the lines of Proposition K is on the horizon for Los Angeles.

“I think L.A. is many years behind San Francisco in terms of sexual politics, sexual rights,” said Mariko Passion, founder of the Sex Workers Outreach Project Los Angeles. “To have an opinion about what sex-worker rights really mean, the awareness is not there at all.”

Patricia West says she moved to San Francisco from Texas in 2007 because of the Bay Area’s reputation for activism. If sex workers are going to earn equal rights through the polls, she said this city is where it’s going to happen.

“This work has afforded me so much – a six-figure income and the ability to travel the world,” she said. “This is my profession. And I’ll keep doing it as long as I’m comfortable, happy and safe.”