Metro police spent almost $120,000 over a three-year period to foster encounters, mostly skin-on-skin, between confidential informants and prostitutes in an effort to further Nashville's crackdown on the illicit sex trade.

Confidential informants pocketed more than $70,000 of that, with the rest going to providers of sexual services, according to police records from 2002 to 2004.

The Police Department stands behind the controversial practice of paying informants to touch and be touched and sometimes go further while gathering evidence of prostitution. But the county's top prosecutor says it is unnecessary and raises a host of legal and ethical issues.

''Certainly, having video and audiotapes of the transactions is valuable,'' said Davidson County District Attorney General Torry Johnson. ''But going beyond that once the transaction has been completed is unnecessary from our point of view and is a little contradictory in letting the confidential informant engage in the very act you're trying to stamp out.''

Johnson praised the department's aggressive approach to ''blights'' such as prostitution and gambling, but said that, in the past, sexual contact between informants and prostitutes was not needed.

''We have made plenty of prostitution cases against the prostitutes, owners, others not only for promoting it, but money laundering and other statutes and have not had to have the informant actually engage in any kind of sexual activity,'' he said.

A Metro police spokesman said the department and district attorney's office were discussing the matter but insisted the practice was essential to infiltrating businesses engaging in prostitution.

Police have had to change their tactics as criminals have learned to thwart older methods, department officials said, adding that it has become increasingly difficult even to engage in conversation about prostitution at a business under suspicion without being nude.

Metro police policy bars officers from taking their clothes off during prostitution investigations.

''What's the greater good?'' asked Capt. Todd Henry, who heads the department's specialized investigations division. ''It may be distasteful to some people, but it's better that we have those places shut down.''

Since April 2002, the city has used anti-nuisance laws to close more than 35 businesses believed to be selling sex, including massage parlors, spas and adult bookstores. City officials also have disconnected more than 100 phone lines linked to escort services.

The money paid to informants and prostitution suspects comes from seizures made in other prostitution and gambling cases.

Metro police pay informants about $300 for up to three prostitution ''buys,'' or transactions, and an extra $100 for each additional buy, department officials said.

''It may sound like officers are paying people to have sex all over the place all the time, but that's just not the case,'' Henry said.

''The point is not to go to completion. Completion is very, very rare.

''We do everything in our ability to get them out without jeopardizing the investigation.''

Henry said there were a variety of tactics police used to get the informants out of sexual situations without compromising a case. He declined to give specifics.

Many of the informants have criminal records and came to police attention through other prostitution investigations.

A certain amount of sexual touching is usually necessary to show that the money being paid by the informant is clearly in exchange for a sexual act, Henry said.

''They can't come back and say there was no intention of performing a sex act,'' he said.

Using informants allows the department to establish that prostitution is an ongoing pattern at a business and not an isolated event. The strategy is aimed at targeting business owners, and not just prostitutes, police said.

Metro Law Director Karl Dean said, from the standpoint of the city's liability, the less contact between the informants and prostitutes, the better.

But he was quick to say, ''I'm reluctant to second-guess what the police have done so far because it's been so successful.''

Information about the involvement of confidential informants has been included in civil nuisance suits brought by Metro government, Dean said, adding that the use of the informants had never been challenged by those businesses.

To make individual arrests, but not look at shutting the businesses down permanently ''is purely a Band-Aid approach and not getting to the heart of the problem,'' Dean said.

Informants can go too far, however, he said.

''We always need to be evaluating whether we're doing it right,'' he said, ''and if we're not, improve.''

A few confidential informants have mistakenly been allowed to progress too far in some interactions with prostitution suspects, conceded police spokesman Don Aaron.

''But that in no way takes away from or negates the successes we've had in scores of cases,'' he said.