For [many] years, sci-fi writers have imagined weapons that might use energy waves or pulses to knock out, knock down, or otherwise disable enemies--without necessarily killing them. And for a good 40 years the U.S. military has quietly been pursuing weapons of this sort. Much of this work is still secret. But now ... the search for weapons that could incapacitate people without inflicting lethal injuries has intensified. Police, too, are keenly interested. Scores of new contracts have been let, and scientists, aided by government research on the bioeffects" of beamed energy, are searching the electromagnetic and sonic spectrums for wavelengths that can affect human behavior. Recent advancements in miniaturized electronics, power generation, and beam aiming may finally have put such pulse and beam weapons on the cusp of practicality. Scientists say they are natural successors to projects already underway--beams that disable the electronic systems of aircraft, computers, or missiles, for instance. "Once you are into these antimateriel weapons, it is a short jump to antipersonnel weapons," says Louis Slesin, editor of the trade journal Microwave News. That's because the human body is essentially an electrochemical system, and devices that disrupt the electrical impulses of the nervous system can affect behavior and body functions. But these programs--particularly those involving antipersonnel research--are so well guarded that details are scarce. "People [in the military] go silent on this issue," says Slesin, "more than any other issue. People just do not want to talk about this."