Los Angeles police say there are becoming more vigilant about child pornography on the Internet. So far this year, the department has made 15 arrests for a variety of offenses involving kiddie porn compared to only six all of last year.\n The figures were revealed in a news conference in which Bernard Parks, police chief, warned parents to keep a close eye on what their children are doing when they go online.\n The police chief said the number of homes with computers has created new opportunities for pedophiles. They are able to trade pictures with other pedophiles easily and quickly and can seek out young victims, he said.\n In Los Angeles, the number of police detectives monitoring sex crimes against juveniles is unchanged. Recently, though, they have been allocating more of their time to pursue pedophiles on the Internet.\n Child porn crime includes producing, distributing and downloading sexually explicit pictures of children as well as soliciting minors on bulletin boards and in chat rooms. It is also illegal to use sexual language in computer conversations with minors. Police who monitor child porn say they are seeing new and different material in recent months, indicating that new victims are falling prey to computer-savvy predators.\n The most famous of those recently arrested by the L.A.P.D. was rock guitarist Robert "Waddy" Wachtel and his wife, Annie. They were booked earlier this month on suspicion of possessing child porn based on images found on their computer.\n Internet commerce and chat is international and most Internet users are outside the jurisdiction of the Los Angeles police force. However, police officials in L.A. say they have been able to locate networks of pedophiles as well as individuals who operate within the city.