FEDERAL and state authorities have agreed to an enormous experiment with nature to save Florida's deteriorating Everglades, but success is by no means assured.Funding for the half-billion-dollar rescue is uncertain, farmers are trying to block it in court, and the Bush administration's proposal to limit the definition of wetlands still threatens this wilderness area. The Everglades covers 2,000 square miles of sawgrass marshes, wet prairie, and sloughs that the United Nations has designated a World Heritage site and International Biosphere Reserve. In dry years, feeding the Everglades will force new water management techniques and conservation on south Florida. In her 1947 book, "The Everglades: River of Grass," Marjory Stoneman Douglas described the wetlands as "a set of scales on which the forces of the seasons, of the sun and the rains, the winds, the hurricanes, and the dewfalls, were balanced so that the life of the vast grass and all its ... forms were kept secure." "It is a haven ... for fish and wildlife that are found nowhere else in the United States," says Carol Browner, head of Florida's Department of Environmental Regulation. Farms and cities have claimed half the original wilderness. Much of what is left is damaged by pollution and by reduced supplies of water. "We're talking about an ecosystem that has been badly degraded over the last four decades," says Robert Chandler, superintendent of the Everglades National Park. It is the most threatened park in the National Park system. The flocks of wading birds - egrets, storks, and ibis - that once darkened the sky have been decimated. Fourteen animal species in the park are endangered, including the Florida panther and the American crocodile. In 1988 the federal government sued state environmental authorities, charging they were not enforcing the state's own water standards and were failing to protect from polluted water the park and the nearby Arthur R. Marshall Loxahatchee National Wildlife Refuge. The state fought back at first, but Democratic Gov. Lawton Chiles, who was elected in November, pushed for an agreement. The first step was the passage this spring of the state's Marjory Stoneman Douglas Everglades Protection Act. Mrs. Douglas has defended the Everglades since the 1940s. The second was a settlement of the suit on July 26 which sets details and deadlines. The settlement identifies two threats to the Everglades: insufficient water, and phosphorus pollution from pesticides in farm-water runoff. The pesticides support new plant species that overpower native plants, which have adapted to water containing almost no nutrients. Cattails, for example, grow so densely that large areas of the "River of Grass" turn into fetid swamp. To decontaminate farm water at least 35,000 acres of filtering marsh land will be set aside. And farmers will have to reduce nutrient contamination. "These components are designed to make sure that water entering each part of the remaining Everglades meets state water quality standards by the year 2002," says Allan Milledge, chairman of the South Florida Water Management District, the state agency that controls Everglades' water. By 1997 phosphorus levels in water entering the Everglades must drop 85 percent. A board of scientists will evaluate the Everglades' recovery and adjust the rescue plan when necessary, but regenerating this complex ecosystem will be difficult. Previous efforts have not always worked. For instance, authorities have provided more water, but scientists now are discovering sudden water releases drowned 90 percent of the hatch in alligator nests two years in a row. The rescue project is a huge experiment with nature, the first of its size and scope. Environmentalists generally have endorsed the rescue, but park superintendent Chandler cautions that other threats have not been addressed, such as mercury contamination and invasions by exotic plants and animals. Washington poses another threat: the Environmental Protection Agency is considering a revised definition of wetlands that would exclude areas now protected. "Half of what is obviously Everglades will not be Everglades under the new definition," says Friends of the Everglades' Joseph Podgor. Closer to home, farmers, especially sugar growers, have already gone to court to block the settlement. "It's not the cleanliness of the water that's a problem. It may be the amount of water they are getting and when they are getting it," says Robert Buker, US Sugar Corporation's vice president of environmental affairs. Farmers could tie up the rescue for years, says Kathy Anclade, spokeswoman for the South Florida Water Management District. Financing is another hazard. The rescue is estimated to cost from $400 million to $600 million and funding is not yet in place. "Political will is going to have to be sustained for the next 10 years," says Ms. Anclade.