CIUDAD ACUNA, Mexico (AP) _ In a handful of cities on the Mexican border, American men still throng to the brothels of ''boys towns,'' legal prostitution zones little changed by fears of sexual disease or campaigns for more wholesome tourism.

At least five Mexican border cities have flourishing boys towns, and though some have been moved away from central tourist districts, they remain popular attractions for businessmen, hunters and teen-agers.

They're accepted with little controversy, although Texas' Republican gubernatorial candidate, Clayton Williams, drew heat after admitting recently that he frequented border brothels during his college years more than 30 years ago because they were the only place to get ''serviced.''

Visiting the prostitutes, Williams said, was just ''part of growing up in West Texas.''

On a Thursday night in Acuna, across the border from the Texas town of Del Rio, about 50 American men mingled with Mexican women at the Hunters Saloon beneath a glittering banner that proclaims in English: ''Welcome Hunters.''

While nude dancers perform on stage, prostitutes lead customers toward the bar's back rooms.

''We're just here to check it out,'' said one Texas man, gazing around the bar. ''This is really mild compared to a lot of places.''

Outside along the dusty streets of boys town - also known as La Zona de Tolerancia or Zone of Tolerance - scattered groups of men from nearby Air Force installations, teen-agers and other Americans wander to bars like the Rio Club and La Camelia.

The half-dozen bars, most only a few years old and well-appointed, are clustered on a small hill along a gravel road south of town. Smaller and older brothels cater to Mexican clients.

A Del Rio businessman in his 40s who has frequented the brothels for more than 20 years says there's little fear of AIDS or other sexual diseases.

''I believe there are more problems with diseases ... in the big cities,'' said the man, who declined to be identified. ''These ladies go to medical checkups. Every week a doctor checks them.''

Dr. Herbert H. Ortega of El Paso, executive director of the U.S.-Mexico Border Health Association, said AIDS is ''almost nonexistent'' among the prostitutes. He credits education efforts by the association and other groups, such as the Pan-American Health Organization that he leads.

Acuna health officials last week cited some prostitutes for not having health certificates and checked them for disease.

Men visiting boys towns say many prostitutes require condoms. Some say the threat of disease limits them to looking.

''It's too much of a chance, going home with something you don't want,'' said a Brownwood, Texas, man who made a side trip to Acuna from a seminar for undercover narcotics agents in Del Rio. The agent, who did not want to be identified, said he was there only to drink and look.

Until the early 1980s, boys town was near the center of Acuna, a city of about 120,000. After residents complained about the noise, the district was moved out of town and the party atmosphere subsided.

Boys towns also flourish in the border towns of Reynosa, Juarez, Neuvo Laredo and Piedras Negras.

Prostitutes come from all over Mexico to earn money at the brothels.

Clients say the women charge $40 to $100 for their services. The prostitutes won't discuss profits.

They say they have no pimps and keep all the money they get except for about $5 per customer they pay the bar for use of a room.

By contrast, the legal minimum wage in Mexico for unskilled workers is $3.90 a day. Mexican workers in some American factories along the border generally are considered well-paid at about $100 a week.

The prostitutes shy away from discussing their personal lives.

Rosalinda, 26, said in her six months in Acuna she has had sex with thousands of men.

Her only complaints are slow nights early in the week and the American youths who come not for sex but to take advantage of Mexico's lower drinking age.

''You don't need them around,'' Rosalinda said in Spanish. ''What do you need them for?''