The Clinton administration acknowledged yesterday that the black-tailed prairie dog should be listed as a threatened species, but stopped short of granting it protection under the Endangered Species Act. Such protection would have imposed restrictions on developers and ranchers. The U.S. Fish and Wildlife Service said that it is dealing with a backlog of other species that need protection more urgently and that it could take as long as two years for the prairie dog to get to the head of the line and be listed as threatened. The feds said the postponement would give state officials, who don’t want a federal listing, the opportunity to implement their own plans to protect the species. Black-tailed prairie dogs once inhabited as much as 100 million acres of the Great Plains, but now live only on about 1 million acres.