Since the Endangered Species Act (ESA) was passed in 1973, more than 1,200 animals and plants have been listed as threatened or endangered — a designation designed to protect species on the brink of extinction. But the landmark legislation has been controversial from the start, pitting environmentalists against property-rights advocates in a protracted debate over the ESA's economic costs and environmental benefits. The ongoing controversy has prevented Congress from reauthorizing the law since 1992, but the Republican-dominated Congress is considering rewriting it, complaining that less than 1 percent of listed species have recovered under the law. Wildlife protection groups, however, claim that proposed, so-called sound-science requirements could end up gutting the law. Meanwhile, the Bush administration says it is committed to encouraging voluntary conservation initiatives and to making the law more responsive to the concerns of private landowners and state and local governments.