A mysterious ailment has killed 14 cranes, including three endangered whooping cranes, and sickened 100 other birds at the U.S. Fish and Wildlife Service's wildlife breeding facility in Maryland, the Interior Department disclosed yesterday.

The Patuxent Wildlife Research Center near Laurel has the world's only captive breeding flock of whooping cranes, and the government has mobilized experts from across the nation in an effort to identify the malady and stop its spread.

The deaths are the worst setback at the center since 1984, when seven whooping cranes died of eastern equine encephalitis, a mosquito-borne disease. Before the recent deaths, the center had 44 whooping cranes, more than 20 percent of the world's population.

Fish and Wildlife Service spokesman Megan Durham said biologists do not believe encephalitis is involved this time, but "they haven't ruled out anything."

According to Durham, the disease appears to be confined to the research center's crane flock, of which more than a third have fallen victim since Sept. 19. The ailment also has killed one endangered Mississippi sandhill crane and 10 Florida and greater sandhill cranes, which are not endangered species but are used as foster parents in the breeding program.

The ailing birds are being treated with antibiotics, fluids and vitamins. "They appear to be improving," Durham said. "The cranes are holding stable now." The last death occurred Sunday.

Autopsies of the dead birds showed evidence of kidney damage, she said, but researchers have not pinpointed the cause of death.

The service summoned a special team from the National Wildlife Health Center in Madison, Wis., and has enlisted help from the Agriculture Department's laboratory in Ames, Iowa, and the University of Maryland at College Park, Durham said.

"They are testing the food, the water, the grass -- everything in the birds' environment," she said. No contamination has been found, she said, but the birds' food and water supply has been changed as a precaution.

The breeding program is part of the federal recovery plan for whooping cranes, which number 160 in the wild. Of those, 133 are in a flock that migrates between Canada and Texas. Using captive-bred birds, the service has established a second flock of 27 cranes that migrates between Idaho and New Mexico.