In 1999, Sweden took the approach of decriminalizing the sale of sex but continuing to punish those who paid for it, prompting even more discussion about the best way to combat the sex trade.

A notable exception to targeting prostitution customers is in the federal system, where prosecutors say johns would have to cross state lines or take advantage of vulnerable victims such as children to justify the expense of a federal case.

Barbara McQuade, U.S. attorney in Detroit, said she does not believe her office prosecuted any of the 30,000 or so clients of a decade-long sex ring that made millions of dollars by dispatching prostitutes nationwide.

‘‘We were looking for the organizers,’’ she said. ‘‘In the federal system, we exercise a lot of discretion because we have scarce resources. We can’t arrest and prosecute every john hiring a prostitute.’’

The law enforcement community is starting to realize that the women in the sex trade are frequently victims of circumstances so cruel that their work is carried out under pressures more common in slavery, said Norma Ramos, executive director of the Coalition Against Trafficking in Women.

It’s all part of changing the public’s perception of prostitution, she said.

‘‘The idea is to discourage men from the notion that they have the right to buy the bodies of lesser privileged women and children for sexual gratification,’’ Ramos said.

‘‘We have to move away from the ‘Pretty Woman’ model and towards understanding that prostitution’s pretty ugly.’’

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