The government's elaborate network for diagnosing bird flu will eventually come down to a sprawling 640-acre campus in the Iowa countryside where strict security is the only hint of the crucial role scientists there could play in a national drama that the country hopes will never materialize.

The security and the elaborate protective clothing the Agriculture Department scientists wear — scrubs, coveralls, rubber boots, protective glasses, hairnets and gloves — looks like a made-for-TV disaster movie.

"These are nice, bright, healthy birds," says veterinarian Michelle Crocheck of four unsuspecting chickens strutting around in their cage.

For now.

If suspected cases of bird flu are found at other screening labs across the country, the future for Crocheck's charges is grim.

The four fowl — and hundreds like them — are key players in a complex testing process at the National Veterinary Services Laboratories that will determine whether the highly pathogenic H5N1 bird flu virus has arrived in the United States.

"Lab diagnosis is definitely the centerpiece of the whole avian influenza response," said Larry Granger, who oversees emergency management for the Agriculture Department.

The labs — normally off-limits to anyone but the scientists who work there — were opened Tuesday to journalists for a walkthrough of the nation's only internationally recognized bird flu testing program.

Researchers test for bird flu, mad cow disease and many other animal diseases on the 640-acre campus near Iowa State University. The sprawling green lawns and low buildings are under tight security.

Known as the H5N1 strain of bird influenza, the virus spread from Asia, where it's blamed for the slaughter of 200 million birds, to Africa and Europe. The virus has killed at least 124 people.

No one knows whether the virus will reach the U.S. or develop into a strain of deadly flu that can be transmitted easily by humans.

To help determine when and where it arrives, the government has begun a massive testing program. The first phase started in Alaska, where thousands of migratory birds will be captured and swabbed. The birds are considered natural reservoirs for bird flu and can harbor hundred of different flu viruses.

Samples will be shipped to a network of laboratories across the country for screening. If a sample contains evidence of the H5 virus, it then gets shipped to Ames, where tests are run over several days to determine if the infected bird carried the H5N1 strain.

First, virus from the sample is injected in bird eggs, which are tested five days later to determine whether it is one of 144 strains of bird flu or whether it is another disease such as Exotic Newcastle, which is harmless to humans but deadly to poultry.

If it contains bird flu, the sample is tested to determine whether it is H5N1 or another of the avian influenzas. Only those testing positive for H5N1 go to the lab with the caged chickens.

Eight of these birds, specially bred and disease-free, are injected with virus from the suspect sample. Perhaps within hours, certainly in two days, the birds will begin moving more slowly, perhaps hunching in the corner of the cage and no longer eating and drinking. Their wattles might turn from bright orange to blue.

"If you lose 75 percent of the chickens, or more, then it's high-path," said Brundaben Panigrahy, head of the lab's avian section, using scientists' shorthand for the lethal strain of Asian bird flu.

Although the test results will be announced publicly, likely by officials in Washington, Granger said this will not be a signal of a threat to humans.

"If we find this virus in the wild bird population, it doesn't necessarily mean there's a human health risk," Granger said. "Likewise, it doesn't mean there is a risk to commercial poultry."

So far, the virus has mostly affected birds. Those who have died from the virus — mostly in Asia — had close contact with infected birds. However, scientists cautioned that the virus could mutate into a form that spreads easily among people and could spark an epidemic.

"Finding it in a migratory bird is an early warning system," Ron DeHaven, head of the Agriculture Department's Animal and Plant Health Inspection Service, said in a recent interview.

"So it would be cause for us to put out an alert, do some additional surveillance testing and do some education and outreach, in terms of practicing good biosecurity," DeHaven said.