Germ warfare: new threat from terrorists.

Imagine a weapon so stealthy it's invisible to spy technology, a weapon that detonates without a sound and begins piling up casualties days before anyone notices something is amiss.

No, this isn't the latest version of Star Wars-it's germ warfare. Though banned by federal law and international treaty, biological weapons pose a new threat, scientists say-this time from terrorists emboldened by the breakdown of international order and the rise of extremism.

"Events in the last few years have eradicated taboos against biological warfare. Once it was thought to be too horrific, now it's just a tool of the trade," says Kyle B. Olson of the Arms Control and Proliferation Analysis Center in Arlington, Va.

"The threat of biological warfare is growing because it is so easy, because it can kill so many people, and because an infectious disease can have a long-lasting impact," asserts Kathleen C. Bailey of the Lawrence Livermore (Calif.) National Laboratory.

Building a nuclear capability would cost $1 billion or more, require 1,300 engineers, and take years. Developing biological weapons could cost less than $100,000, require five biologists, and take just a few weeks, using equipment that is readily available almost anywhere in the world.

Moreover, the secrets of cultivating germs are not secret at all-they are described in scientific literature, Bailey said at a meeting this week on the threat of infectious disease.

Extremists have already obtained the tools of biological warfare. Last year, an Ohio militia enthusiast was arrested after he sent away for and received plague virus from the American Type Culture Collection in Rockville, Md. In Japan, Aum Shinrikyo-the cult that spewed poison gas into Tokyo subway stations-built a germ warfare lab and tried to get Ebola virus.

A germ warfare lab is difficult to detect, Bailey said at the meeting, sponsored by the nonprofit National Consortium for Genomic Resources Management and Services in McLean, Va. Through 25 United Nations inspections, Iraq successfully hid five labs that made thousands of liters of the germs that cause anthrax, botulism, and gas gangrene. Finally, a defector-inspired raid on an Iraqi farm in 1995 unearthed incriminating documents.

Western nations probably face the greatest risk of germ warfare because their populations are extremely mobile. "You don't know you've been struck until the blow is 2 or 3 days old," says Olson.