Warning that "congressional hysteria over security" threatens the quality of science at America's nuclear weapons laboratories, Energy Secretary Bill Richardson said yesterday he will begin issuing waivers for foreign scientists to visit the national labs again.

Richardson said the waivers are permitted under a new law that imposed a moratorium on visits to the Los Alamos, Lawrence Livermore and Sandia National Laboratories by scientists from China, Israel, India, Pakistan and other countries deemed sensitive.

The freeze in scientific exchanges and other efforts to tighten security--such as severe restrictions on outgoing electronic mail--began last spring and summer amid a political furor over allegations that China stole U.S. nuclear secrets from the labs, which belong to the Energy Department.

"As a result of congressional hysteria over security, we are in danger of losing the science that we sought to protect," Richardson said in a telephone interview. He added that he wants to "restore the proper balance between security and science."

At the heart of Richardson's concerns, however, are steps that he initiated to tighten security and that Congress subsequently endorsed or took further. His suggestion early this year that polygraph tests be given to employees handling top-secret information, for example, was later put into law by Congress. But it has engendered strong opposition from scientists worried about the incidence of false results in such "lie detector" exams, and Richardson said the latest plan is to require testing of only "several hundred" scientists at each lab, far less than the 5,000 to 10,000 subjects originally envisioned.

Richardson's decision to scale back some new security programs was triggered in part by a National Academy of Sciences study, released last month, that emphasized that "both secrecy and scientific openness contribute to our security." At present, the study concluded, "far more attention is being directed toward avoiding the risks of potential espionage than toward ensuring that we realize the benefits of a properly balanced policy."

The directors of the national labs also have warned that the recent focus on security is having a "chilling effect" on efforts to recruit scientists to work at the laboratories, according to Richardson, who quoted President Harry Truman on the spy hunting of the 1950s: "We cannot drive scientists into our laboratories, but if we tolerate reckless or unfair attacks, we can certainly drive them out."