Of all the millions of new jobs created by the Internet, Randy J. Aden has the one that is, arguably, the most completely not fun.

Aden is the supervisory special agent in charge of a squad that hunts down and arrests sexual predators of children, criminals who use the Internet not only to generate and trade in child pornography, but who enter cyber-chat rooms to engage in sexual talk with minors--and in some cases, then travel to meet with them.

Aden's undercover operation, the first in the FBI targeting the Internet and the sexual exploitation of children, works out of the 15th floor of the Federal Building on the west side of Los Angeles. Because of the nature of their work, the handful of agents under Aden toil in a secure corner of the building, away from other agents, because he understands that the material on their desks would be deeply disturbing to co-workers.

The modus operandi of the operation is for agents to enter chat rooms, posing as minors, and engage in electronic conversations with possible predators looking for sexual kicks, mostly white males who want to talk with 13-year-old girls about sex and their fantasies. They troll for their quarry in rooms with names such as "dad&daughtersex."

The operation, called the SAFE team, for Sexual Assault Felony Enforcement, made its most high-profile case in September, when team members arrested the young software impresario Patrick Naughton, when he was lured to the Santa Monica Pier to meet who he thought, according to the FBI, was a 13-year-old girl after chatting with her (or the agent posing as her) on and off for seven months.

The case, which goes to trial today, is sensational because Naughton is one of the authors of the breakthrough computer language Java, was head of technology at Infoseek Corp. and was about to assume a leadership post at Walt Disney Co.'s Internet subsidiary.

What does Aden look for in an agent to work such cases? Aden, a trim man with graying hair in a starched white shirt and shiny FBI shoes, ticks them off: strong work ethic, imaginative, resourceful, good at thinking on his or her feet and "a good sense of humor."

Why a good sense of humor? "Because it keeps you going," he said, in an area of law enforcement that is widely seen as the most grim.

Aden is not a stranger to the field. He worked as a police officer in nearby Simi Valley for 10 years, and two of those he spent in the juvenile unit, investigating cases of abuse, neglect and molestation.

"It had," he says, "just an incredible impact on me. It's rewarding. But it burns people out. You're dealing with the victims, and they can be so very, very defenseless and vulnerable."

Aden and his agents do not get specialized training in how to act on the Internet like teenagers. "You just pick it up from the popular culture," he said. They read magazines, keep up with the slang and watch "Buffy the Vampire Slayer" on television. Plus, some of the agents have kids themselves.

While the activities of the SAFE unit have not been exactly kept secret, Aden says that its case load continues to grow. Since setting up shop two years ago, the SAFE team has arrested 19 "travelers," as they call them, men who cross state lines to meet with the phony young quarry.

As Aden sees it, the men who look for young sex partners on the Internet build fantasies around their encounters, but the fantasy usually does not include the prospect of getting caught. They are risk takers. Many of those arrested, too, seem to believe that because they use code names on the Internet, they cannot be found. But a search warrant or subpoena usually produces a real name.

"The myth of anonymity on the Internet," Aden said, "is just that: a myth."

As the Internet grows and expands, with all its usefulness and empowerment, so, too, does child pornography and illegal sexual talk between adults and children.

But the work of the FBI and other agencies is controversial. One defense offered by those arrested is that they were just talking about sex, and that the Internet is filled with people acting out their fantasies with other "role players" and that nobody really knows who anyone is on the Internet.

Aden is not impressed by that argument. "We repeatedly inform the people we are communicating with that we [the agents] are underage children," he said.

Aden says he is disturbed by the presence of what he calls "Internet tar pits," sites that bring users to pornographic sites and then make it hard to get out.

Asked how closely he would recommend a parent monitor a child's Internet use, Aden said, "Right over their shoulders."

Players

Randy J. Aden

Title: Supervisory special agent, head of Sexual Assault Felony Enforcement Unit, Federal Bureau of Investigation.

Age: 47.

Education: Bachelor's degree in criminal justice, University of Nebraska; master's in public administration, California Lutheran University, Thousand Oaks, Calif.

Family: Divorced, two children.

Previous work: Police officer.

Pastimes: Riding his Harley.

CAPTION: Special agent Randy J. Aden directs the undercover SAFE team, the first in the FBI targeting the Internet and child sexual exploitation.