The government is adapting environmental monitors scattered across the nation to detect bioterrorism, hoping they will provide early warning if smallpox, anthrax or other deadly germs are released into the air.

The system would retrofit many of the 3,000 existing environmental monitoring stations with new filters to detect biological agents, administration officials said.

"It's part of our precautions to protect the country," White House spokesman Ari Fleischer said Wednesday. He added that the White House has no specific information about a pending threat.

Results of the early warnings could be confirmed at a network of laboratories within 24 hours using DNA analysis.

The system was tested throughout 2002, including at the Winter Olympics in Salt Lake City.

Nightmare scenarios envisioned by bioterrorism experts include a small plane flying above a community, releasing anthrax or other germs over a large gathering of people. Depending on the winds, thousands of people could become ill, yet it could take days to figure out what happened.

The sooner health officials detect a bioterrorism incident, the sooner they can properly treat victims with vaccines or antibiotics and protect others who might become infected.

Monitoring systems now run by the Environmental Protection Agency will be adapted to check for a number of biological agents. The systems, which filter air, were created to measure pollutants and the quality of the air.

If a station detects something suspicious, samples would be sent to the closest of some 120 labs that are part of the federal Centers for Disease Control and Prevention's Laboratory Response Network. Results from these labs would be available within 12 to 24 hours, depending on the tests being conducted.

The tests involve genetic analysis using polymerase chain reaction, or PCR, techniques. They examine the genetic fingerprint of a germ sample and make a quick and accurate determination as to what it is.

These tests are considered much more reliable than hand-held devices often used by emergency responders, which often indicate the presence of a particular germ when none is there.

The new system is intended to work with existing patient surveillance systems, which monitor symptoms of patients, looking for strange patterns of disease that may detect a biological agent infecting many people at the same time.

The system, first reported in Wednesday's editions of The New York Times, is being created by the new Homeland Security Department. It will cost about $1 million to upgrade each monitoring system and an additional $1 million per city, per year, to run the system, analyzing samples that are collected.