It's lovely to sit back and watch the often-spectacular wildlife photography on PBS' National Audubon Specials. Tonight's hour-long program about North American ducks is no exception: Beautifully done, it follows the migration routes and the problems of mallards and canvasbacks, pintails and wood ducks, as well as some of their brothers.

But executive producer Christopher Palmer also has a harsher, more immediate message: We're fouling up. It's the wildlife and the land that pay for our greed, initially, but the loss is really ours.

"Birds are an index to the health of the land," says one waterfowl biologist. "The ducks are trying to tell us that the land is not in the state that it should be."

In the ecosystem, human lives are inextricably entwined with those of other creatures and the land that supports both. Ducks, we're told tonight, are losing ground rapidly.

But the National Audubon Society is concerned about conservation in general, not just the fate of birds. Next week's installment, narrated by Dennis Weaver, focuses on efforts to persuade the American farmer to cut back on herbicides, pesticides and chemical fertilizers that pollute the land and water and ultimately the food we -- and the animals -- eat. Some believe individual farmers can be persuaded to use alternative methods, such as low-chemical farming, ridge-tilling and integrated weed management, but likely not the agribusinesses intent on producing an overabundance of crops for large profits.

On Aug. 16, the eighth installment in the series looks at the endangered African cheetah and the Florida panther, cousin to the mountain lion, which lives in the Everglades. Less than 30 panthers remain, many of them killed by vehicles that travel Alligator Alley between Naples on the gulf coast and Fort Lauderdale on the east. Both panthers and cheetahs suffer from the results of a diminishing habitat that results in inbreeding and its effect, the inability to reproduce.

For the story on Florida panthers, narrated by Loretta Swit, Palmer and cinematographers Wolfgang and Sharon Obst took Peter Strohs, 59, of the sponsoring Strohs Brewery Company, into cold swamp waters of the Everglades. Strohs, a bird hunter and fisherman, has been a member of the National Audubon Society board for nearly two years, does fundraising for Ducks Unlimited, is a trustee for Conservation International, and is on the board of Robert Redford's Institute for Resource Management.

Tonight, John Heard narrates "Ducks Under Siege" and tells us that the duck population is at its lowest in 30 years: There are only half as many mallards as there were in 1955 and only 31 percent of the pintail duck population. The reasons: poisoned drain water from farms, agricultural practices in the northern prairie regions of the United States and south-central Canada, and the death of marshes in the South. Ducks, who cannot feed in open water, need the shallow wetlands for eating and breeding, and as stopover points during the seasonal cross-continental migrations.

"Their habitat is under attack," says Heard. More than half is already gone, and the rest going fast.

In California, more than 90 percent of the wetlands have already been lost to farming, forcing ducks into the little remaining water, where outbreaks of botulism and cholera have killed as many as 70,000 at one time. Drain water from farm fields contains poisonous levels of selenium, polluting the soil and making it dangerous for ducks to to eat insects hatched there. Those that do often produce deformed ducklings.

Competition for the water pits California farmers against wildlife advocates. While farmers protest that they and everyone employed in farming must make a living, environmentalists point out that much of what is grown in the San Joaquin Valley is in surplus supply. The bottom line, says wildlife photographer Gary Zahm, is that "ducks don't vote."

In the Louisiana Delta, 750,000 acres of wetlands have disappeared in two decades because of flood control levees and canals cut for shipping that allow salt water to flood the freshwater marsh, killing the plant life the ducks fed on.

There, because ducks are crowded into smaller areas, some are being overhunted. Ironically, the sale of duck hunting stamps raises money for wetlands preservation, so that if the United States Fish and Wildlife Service decides to curtail the hunting of ducks, less money will be able to preserve wetlands.

In the north central prairie region of the United States and the south central area of Canada, ducks look for glacial potholes where they can raise chicks. But farmers, who dislike having to plow around potholes and are always looking for more tillable land, prefer to drain them. Half of the potholes the ducks depended on in the Dakotas have disappeared in 30 years.

Nesting ducks are also in danger from farm machinery that runs over the nests and cuts back the grasses that serve as camouflage. Already, says Heard, 90 percent of ducklings there are killed by predators, mainly coyotes and foxes.

And then there's another threat: civilization. Every acre of wetlands in Alameda County, California, is slated for development, a situation so distressing that conservationists and hunters have banded together to fight the developers. Temporarily, a tiny mouse has come to the rescue. The discovery of the endangered salt marsh harvest mouse provided a reason for the group to get a court injunction to stop development.

In New Jersey, there's a happy story. Brigantine Wildlife Refuge, nine miles from Atlantic City, was in danger of becoming polluted by the 800 homes that a developer planned to build. Brigantine is a key site along the flight path of ducks flying south, particularly the black duck, which is down to 60 percent of its 1955 numbers.

Taken to court by environmentalists, the firm sold the project to another developer, who agreed that saving the environment was worthwhile. He set aside 1,000 acres, in perpetuity, for wildlife, decided to forgo the planned golf course, cut the projected number of houses by one-third, gave up other plans, and still believes he made a good business deal.

There are other areas for hope, too: Even though much of the land in the United States and Canada is being eroded and exhausted, the 1985 United States Farm Act included a provision to take marginal land out of farming. Canada has a program to teach its youngsters about environmental conservation, and is engaged in a research project to provide a "safe zone," a small peninsula bordered by electric fencing, to see if ducks will nest there, safe from predators. The U.S.-Canadian North American Waterfowl Management Plan is a joint project to stop and even reverse the decline of our water wildlife.

So "Ducks Under Siege" ends on a slightly optimistic note. From the fear of California wildlife artist Wally Peters that "Nobody's going to have a place to go any more to see a duck," Heard concludes that "there is still time to save the ducks and the marsh ... to save something for tomorrow."

The next Audubon Special, the eighth in a series of 12 coproduced by the National Audubon Society, Turner Broadcasting System and WETA here, is slated for December and will focus on whales. Like all the Audubon projects, it will concentrate on the impact of people on natural resources and wildlife.

The companion book to this series of specials is called Life in the Balance (Harcourt Brace Jovanovich, $29.95) by David Rains Wallace. The title seems to sum it up.

CONTINUED ON PAGE 38 CONTINUED FROM PAGE 9 PHOTO BY LARRY ENGLE "Ducks Under Siege" (Sunday on 26) looks at the decline in the duck population due to their diminishing habitats.

BY FRED SIBLEY, U.S. FISH AND WILDLIFE SERVICE North America's rare California Condor. BY DEAN BIGGINS, U.S. FISH AND WILDLIFE SERVICE The endangered black-footed ferret.

PHOTO BY PETER J. VAN HUIZEN A particularly heavy concentration of ducks at Sacramento National Wildlife Refuge in Willows, Calif., one of the ducks' few remaining habitats.