What's more, they were hearing.

Officials say that as they searched fruitlessly for Eric Robert Rudolph — the fugitive suspect in last January's Birmingham, Ala., clinic bombing — apparent Rudolph sympathizers were successfully listening in on radio and telephone transmissions throughout the area.

Despite the difficulty of capturing the type of signals used today, these people apparently were employing new, sophisticated equipment to good effect.

"We know that they were monitoring cell phone traffic in North Carolina," says James Cavanaugh, the ATF's special-agent-in-charge who was then leading the manhunt. "There are people out there who were making great efforts to run communications surveillance, to listen to all the business of government agents."

It's not known precisely what the eavesdroppers heard, although it is evident that antigovernment activists learned where many agents were running their operations.

What is also clear is that more and more hard-liners in the antigovernment movement are using expensive electronics to spy on law enforcement, military operations, news reporters, public utilities and other strategic facilities.

And that has many observers deeply worried.

'At Their Fingertips'
"There are a lot of technicians in the movement, people who have gotten their training in the military," says Oliver "Buck" Revell, retired deputy associate director of the FBI. "The Internet and the communications they're capturing give them more intelligence than they've ever had in the past.

"And because the movement includes active members of law enforcement, the military and the National Guard, they also have access to vast amounts of human intelligence. It's all right there at their fingertips."

Not long ago, the most electronics buffs could do was listen in on police and emergency radio traffic on their scanners. But soon, they were able to monitor analog telephone signals sent via repeating towers.

Now, thanks to breakthroughs in "trunking technology" people can listen in — illegally — to cellular phones, even though these signals often jump frequencies every few seconds. Sophisticated systems use home computers to reassemble the fragmented transmissions into speech.

In the last few years, movement activists have sought to gather intelligence in a variety of ways. They've distributed forms seeking data on everything from military movements to the operations of public utilities, and they've put up Internet pages seeking information on individual law enforcement and other officials.

A few have apparently even managed to hack into well-defended computer systems.

Now, such operations seem to be spreading.

"All agents are counseled to be absolutely concerned about this kind of activity," says Cavanaugh. "Number one, cell phone communication is not secure. Number two, if you're not on encrypted radio, your communications are being heard."

In North Carolina, most law enforcement traffic was encrypted — either using the STU-III system for fixed telephones or other systems to code radio traffic. But agents can drop their guard, particularly when using cell phones to talk to local law enforcement agencies.

In addition, news reporters — who sometimes are working on tips that even agents don't have yet — normally use cell phones to talk to their offices.

"When the FBI, ATF and the media were out here looking for Rudolph, anyone with a scanner could listen to the news crews," says Bob Grove, publisher of North Carolina-based Monitoring Times, an electronics magazine specializing in scanners.

"And occasionally, even the FBI and ATF conversations could be heard because they didn't encrypt everything."

Bugs, Beepers and Laser Beams
The variety of surveillance devices is remarkable. A sampling:

· Window bounce lasers. If aimed at a window at exactly the right angle, these devices send a laser beam that captures the vibrations made by a conversation inside. The vibrations are then translated and amplified, allowing the listener to eavesdrop.

· Miniature video cameras. No bigger than a credit card, these devices can be hidden almost anywhere and are capable of transmitting images to a viewer at a remote location. Peephole cameras also are available that can shoot through a 1/16th-inch hole.

· Wireless bugs. These audio transmitters can be hidden virtually anywhere. Although illegal, they can be acquired relatively easily from unscrupulous distributors and are said to be selling faster than any other spy device.

· Bumper beepers. Secreted beneath gas tanks or bumpers of vehicles, these tiny transmitters allow the spy equipped with a receiver to track movements of police or other targets. At more than $1,000, they're more expensive than most equipment.

· Night vision binoculars. These telescopic devices utilize infrared light, not visible to the human eye, to allow spies to work under cover of darkness.

Most of this equipment, along with much else, can be bought legally, although officials have shut down some "spy shops" that have illegally sold certain types of equipment.

Dozens of distributors advertise in such publications as Monitoring Times, Nuts & Volts Magazine and Spycomm. Many publications and Internet sites also detail how to build equipment.

'A Revolution in Technology
Radical right groups have been involved in intelligence-gathering and countersurveillance for years, especially since the 1995 Oklahoma City bombing.

That summer, three such groups — the Tri-State Militia, the Militia of Montana (MOM) and the neo-Nazi Aryan Nations — simultaneously launched intelligence campaigns by asking members to begin covert reconnaissance.

They distributed hundreds of "S.A.L.U.T.E." forms, the name of which stands for size, activity, location, unit, time and equipment — the information the groups wanted spies to collect.

Later, the underground League of the Silent Soldier produced a 14-part operations manual that described how to monitor the radio traffic of local and federal law enforcement agencies. The manual was found with a Florida bomb-builder arrested last year.

In 1996, MOM and a New Hampshire group formed the Un-American Activities Intelligence Committee, apparently to gather information on their enemies. The same year, an Arizona antigovernment group known as the Viper Team used video cameras to surveil government buildings in Phoenix, allegedly as potential targets.

By 1997, another effort was under way. The American Constitutional Militia Network, a coalition of 15 militias, distributed its "Intelligence Gathering Guidelines." The guidelines asked supporters to document troop movements and to develop sources for information about security at sensitive civilian and military installations.

And just this April, federal officials said in court documents that three men allegedly plotting a bombing and assassination campaign in Michigan had obtained a sophisticated device to counteract electronic surveillance. The North American Militia members also had developed their own intelligence report form, officials said.

All of this worries the ATF's Cavanaugh.

"The revolution in technology has changed things," he says, recounting how notes were left in North Carolina motels last February to let agents know they were being watched. "Law enforcement officers really need to understand that."