The Clinton administration will send to Congress today the centerpiece of its ambitious plan for restoring the Florida Everglades, a proposal for federal and state governments to spend $7.8 billion over 20 years on a giant re-plumbing project that would attempt to mimic natural water flows across South Florida.

With Vice President Gore promoting the plan and congressional Republicans threatening to cut off funding without stronger environmental assurances, the debate over Florida's water is developing into a major campaign-year battle.

The administration plan, designed to mitigate some of the environmental damage done over the last half century by flood control and water projects that have spurred Florida's urban and agricultural growth but cut the size of the Everglades in half, is "the most critical step yet to restore . . . one of America's true treasures," Gore said in a statement.

Developed over several years by more than two dozen federal, state and local agencies led by the Army Corps of Engineers and the Department of Interior, the complex plan would nearly double the amount of fresh water now available in South Florida and ensure that 80 percent of the increase flows to the Everglades--and at the right times of year. Much of the remainder would be available for municipal use in a state whose population is expected to double by the year 2050.

A draft of the plan was unveiled last October to sometimes hostile reviews by environmentalists, the National Park Service and scientists concerned about the degradation of one of the world's largest and most biologically important wetlands.

Since then, the plan has been toughened significantly, with more water earmarked for Everglades National Park, a shorter timetable for completion of many of the five dozen individual engineering projects, and creation of a scientific panel to monitor its success.

In addition, in its letter to Congress accompanying the plan, the Corps of Engineers has declared unequivocally that its "primary and overarching purpose" is to "restore the south Florida ecosystem." To that end, the Corps pledged to work with other federal and state agencies to ensure the plan is carried out.

To Everglades advocates in the environmental community and on Capitol Hill, ensuring that Florida water officials comply with the plan is crucial in a state where politically powerful urban and agricultural interests compete for water with the Everglades.

On Tuesday, for example, the House Appropriations Committee voted to withhold $42.4 million in land acquisition funds for Everglades restoration until the Clinton administration nails down an agreement with Florida specifying adequate water supplies to "ensure a restored ecosystem." The land acquisition program is a separate feature of the administration's overall restoration plan announced in 1996.

Although he has supported Everglades restoration, Florida Gov. Jeb Bush, the Republican brother of Texas Gov. George W. Bush, declined invitations to attend today's Capitol Hill announcement.

The administration's plan must be authorized by Congress in legislation that will be considered next year.

The plan going to Congress grew out of a study commissioned in 1992 of ways to undo the environmental damage caused by the massive Central and South Florida Project, which encompasses about 1,000 miles of canals and levees and 16 major pump stations. The project has fragmented and disrupted natural processes in what was once a massive, slow-moving, shallow lake by diverting billions of gallons of fresh water a year out to sea, and by impeding the southward movement of water. Among the victims are wading birds, whose populations have declined by as much as 90 percent.

The overall goal of the 20-year plan to be jointly funded by Florida and the federal government is to re-create as much of the natural system as possible by adding water, ensuring it flows at the right time, and by dismantling barriers to its southward journey across a project area that covers 18,000 square miles stretching from the Kissimmee River drainage in the Orlando area to Florida Bay.

To reestablish the "sheetflow" of water through the Everglades, 240 miles of canals and levees will be removed, and 20 miles of the Tamiami Trail, the highway that cuts across the heart of the Everglades, will be rebuilt to allow water passage underneath.

To store water so it is available for both the Everglades and Florida's booming metropolitan areas, a network of surface reservoirs and underground storage systems will be built. And to help treat urban and agricultural runoff, some 30,000 acres of man-made wetlands will be created, in addition to the more than 40,000 acres already being built.

Environmentalists are generally enthusiastic. "We think it's a very good plan," said Ron Tipton, a veteran Everglades advocate who serves as director of U.S. eco-region conservation for the World Wildlife Fund. "You're going to have the volume of water you need to deal with the wet-dry cycle of the Everglades."

Tipton and other environmentalists, however, would like to see more agricultural acreage converted to water storage. "Engineering alone won't save the Everglades," said Frank Jackalone, the Sierra Club's representative in Florida.

Staff writer Ceci Connolly contributed to this report.

CAPTION: The image of a white heron is reflected in a canal in the Florida Everglades, subject of a massive environmental restoration plan.