WASHINGTON—The government acknowledged that an outbreak of one of the most contagious animal diseases from any of five locations being considered for a new high-security laboratory—an event it considered highly unlikely—would be more devastating to the U.S. economy than an outbreak from the isolated island lab where such research is now conducted.

The 1,005-page Homeland Security Department study, released Friday, calculated that economic losses in an outbreak of foot-and-mouth disease could surpass $4 billion if the lab were built near livestock herds in Kansas or Texas, two options the Bush administration is considering. That would be roughly $1 billion higher than the government’s estimate of losses blamed on a hypothetical outbreak from its existing laboratory on Plum Island, N.Y.

The administration is studying the safest place to move its research on such dangerous pathogens from Plum Island to the U.S. mainland near herds of livestock, raising concerns about a catastrophic outbreak. A final choice is expected by late fall. The foot-and-mouth virus does not infect humans but could devastate herds of cattle, swine, lambs and sheep.

The five locations the U.S. is considering are Athens, Ga.; Manhattan, Kan.; Butner, N.C.; San Antonio; and Flora, Miss. A sixth alternative would be construction of a new research lab on Plum Island. That option is considered less likely because the administration spent considerable time and money scouting new locations and because of financial concerns about operating from a location accessible only by ferry or helicopter.

Economic losses in an outbreak would exceed $3.3 billion if the new lab were built in Georgia, North Carolina or Mississippi, the report said. It calculated losses of $2.8 billion in an outbreak from Plum Island.

The Homeland Security official in charge of the study, Jamie Johnson of the Office of National Laboratories, said it sought to identify specific risks to each candidate location.

“What the EIS (environmental impact statement) concludes is that the likelihood of release of foot-and-mouth disease is extremely low,” he said. “However, in the event that foot-and-mouth does get out, what does that mean to these sites?”

The new study concludes that risk would be low to nonexistent that an accident or terrorist attack would result in the outbreak of a dangerous pathogen at any of the sites except in case of a fire and explosion. Such a fire and explosion would pose a moderate risk that virus or disease could spread to nearby livestock or wild animals.

The threat from fire and explosion would be diminished for the government’s isolated laboratory on Plum Island “due to the low likelihood of any disease getting off of the island,” the report said.

The new National Bio-and Agro-Defense Facility would replace the existing 24-acre research complex on Plum Island, which is about 100 miles northeast of New York City in the Long Island Sound. Besides foot-and-mouth disease, researchers also would study African swine fever, Japanese encephalitis, Rift Valley fever and the Hendra and Nipah viruses. Construction would begin in 2010 and take four years.