Snow geese circle, rise and circle again before settling in a greening meadow. A blue heron glides low over a dark pool framed by bronze cattails.

There is silence except for the riffling water and the rustling reeds. And the popguns, testament to good works gone awry.

The government's propane guns, noisy but harmless, boom across the Kesterson National Wildlife Refuge here every few minutes, scattering ducks, herons and geese to flight from a placid reservoir that has become a deathtrap.

Birds that disregard the guns and nest here produce grotesquely deformed offspring -- chicks without eyes, without legs, with twisted wings, contorted beaks, and brains protruding through malformed skulls.

Kesterson is contaminated with selenium, a naturally occurring element now dangerously concentrated in the waters of the refuge as a byproduct of the way man has rerouted water across this state for purposes of agriculture.

For years vast amounts of water have been brought from the north to the San Joaquin valley south of here; a desert has been transformed into one of the nation's richest agricultural areas. But because the valley has an impermeable floor, the water could not escape until the government also built a drain, a ditch back to the north.

That ditch now ends in the refuge, carrying not only used water but salts and minerals leached from the valley's soil. The selenium is one of these.

Once a haven for egrets, white cranes and grebes, the refuge now lies at the heart of the latest controversy over the water-intensive farming practices of central California. The battle this time is over repairs, whether to stop the irrigation water, find some way to treat it or find some other place to put it -- and who will foot the multibillion-dollar bill.

Farmers here, confident that Washington will not turn its back on the cornucopia that it created, say they expect the Treasury to come to their rescue.

The drainage ditch, called the San Luis Drain, was not intended to end here. If completed, at a cost estimated at nearly $5 billion, the drain would carry Kesterson's selenium-laden water to the watershed above San Francisco Bay, from which the state pumps drinking water south to Los Angeles.

"The only way to stop producing the water is to stop irrigating the land," said William Johnston, manager of the Westlands Water District, the largest importer of water in the western San Joaquin valley. "If the land can't be drained, it will go out of production."

Federal officials say the cheapest way to clean up Kesterson would be to close it, and the San Luis Drain as well, with "serious adverse economic consequences" for the valley's farmers. More than 40,000 acres of farm land would go out of production, according to the Interior Department.

But farmers here contend that the impact would be far greater, potentially threatening more than 1.5 million acres in the western San Joaquin.

The valley's agricultural interests have come up against the formidable problem of toxic waste. And the farmers' traditional foes, armed with the stark evidence of the polluted reservoir, are determined to make Kesterson a symbol of what they view as the folly of national water policy in the West.

"I don't want to say it's insoluble," said Albert Meyerhoff, an attorney with the Natural Resources Defense Council. "But there's going to be a significant economic crunch. And a good part of the land that has been put into production may well have to be taken out."

Bill Davoren, a former Interior Department official who heads the Bay Institute, a San Francisco-based conservation group, is more direct.

"They should have known better than to put good river water in there to start with, and they're going to have to start relocating that water to land that is not so mineralized."

At the root of this dilemma is geology. The San Joaquin valley's western slope, blessed with a benign climate and fertile ground, is considered prime farm land. By the measure of productivity and price, it is. Land goes for $3,500 an acre and produces, with the help of irrigation, up to three times the yield of non-irrigated lands elsewhere.

But the soils are laced with the salts and minerals of the sea bed it once was, and the vast, flat fields are underlaid by impermeable clay.

Add irrigation water and the land blooms -- for a time. As water pools above the clay, the soil becomes saturated. The rising water table drowns roots and pushes salt to the surface in crusty white patches.

"They've got a flowerpot without a hole up there," Davoren said.

The federal Bureau of Reclamation, which designed and built the massive Central Valley Project that waters the western San Joaquin, anticipated the need for drainage and 30 years ago set about to create a hole for the flowerpot.

In the 1960s, with political help from the area's well-connected farmers, the bureau persuaded Congress to approve $700 million for the San Luis Drain. The drain was envisioned as a 200-mile canal that would carry waste water back north.

The money ran out in 1975, with the drain more than 100 miles shy of its eventual drainage point in the Sacramento-San Joaquin delta above San Francisco. The terminus was the Kesterson reservoir, a 1,200-acre complex of ponds that was set up to do double duty as a wildlife refuge and a regulating reservoir for the drainage system.

For several years, while the bureau laid drain pipes under farm land, the reservoir was filled with fresh irrigation water from the Delta-Mendota Canal. Then, in the late 1970s, farmers began laying drainage tiles under their fields and hooking them into the San Luis Drain.

Waste water began to flow into Kesterson, with dramatic effect.

Gary Zahm, who came to Merced County in 1981 to manage the Kesterson refuge and other federal wildlife preserves in the western valley, said he knew immediately that something was amiss in the reservoir.

"I didn't see the diversity of life. I didn't see muskrats, crayfish, turtles," he said. "After 18 years of working in marshes, it just didn't look right."

Only tiny mosquito fish remained in the brackish waters.

Zahm, suspecting something akin to a pesticide spill, called in a team of biologists. The verdict came in December 1982: Sediment from the reservoir was contaminated with concentrations of selenium more than twice what would qualify it as hazardous waste under federal law.

Water showed selenium at levels up to 4,200 parts per billion, more than 400 times the level considered safe for drinking. The mosquito fish showed the highest concentrations of selenium ever found in living creatures -- up to 53 parts per million.

At the same time, biologists started finding deformed nestlings, evidence that selenium was working its way up the food chain.

"That was the first indication anybody had that there would be a problem with the drainage water," Johnston said. But more tests showed that the problem was not confined to Kesterson.

Farmers and federal officials had studied the drainage problem here for decades, mainly concentrating on salts and boron, another abundant mineral that at high concentrations can damage plants.

But somehow selenium escaped notice.

"We knew when we imported the water this would happen," said Dan Nelson, manager of the Broadview Water District, one of 30 irrigation districts in the western valley. "We all thought Kesterson was as efficient as hell. But we didn't know about the selenium. We had enough problems without the selenium."

Last month the state Water Resources Control Board gave the Bureau of Reclamation five months to design a cleanup plan for Kesterson and three years to put it into effect.

The bureau argued that the situation cannot be corrected so quickly.

Alternatives to the San Luis Drain have been suggested, but most of them involve even more expensive strategies (such as desalinization) or alternate dumping sites that have political opponents.

At one time, farmers thought of draining their waste water into Nevada's Mojave Desert, but the selenium discovery has stiffened resistance there. Another possibility is ocean discharge near Monterey, Calif.

"The real hard fact is that by adopting this order the board may force 42,000 acres of prime agricultural land out of production," bureau regional director David G. Houston told the board.

Three thousand of those acres belong to Darrell Silveira, who grows cotton, sugar beets and alfalfa in the western San Joaquin. Silveira's farm was one of the first to need drainage.

"My grandfather took this land out of sagebrush," he said. "Now, just one phone call and I'm bankrupt."

There is no denying the benefits that imported water has brought Silveira. He pays $21 for enough water to flood an acre the depth of one foot, and he uses about 9,000 acre-feet a year.

But the real cost of that water is $53 an acre foot, according to Silveira, which means the federal government subsidizes his irrigation at the rate of more than $280,000 a year.

Silveira and other farmers here contend that they cannot afford to dispose of the excess water.

"We might have to go to the taxpayer for some help," district manager Nelson said. "That's not out of line, given the advantages the taxpayer gets from irrigated agriculture."

Adds Silveira: "If there's no other solution but to put me out of business, I can accept that. But to cut off the ocean for disposal would condemn agriculture as we know it."