On the surface, Pyrite Canyon looks like a choice picnic spot, a wedge of southern California turf flanked by jagged hills and carpeted with hearty sunflowers.

But beneath the tableau lies a stream of man's most lethal chemicals, cyanide solutions, acids, heavy metals and pesticides, the industrial debris of corporate America dumped here in the 1950s and 1960s by enormous tank trucks and left to ooze into the underground water supply of the 7,000 people of this rustic community.

Pyrite Canyon was once home of the Stringfellow Acid Pits, a toxic-waste site. Originally it was welcomed as a lure to industry and jobs. Instead, Stringfellow brought environmental havoc to Glen Avon: property loss, livestock deaths and human illnesses, including high rates of cancer and heart trouble. More ominous is the poisonous horizontal plume that is spreading underground as fast as three feet a day toward the Chino Basin, which provides water for 500,000 people within a 30-mile radius.

This toxic liquid has seeped from the pits despite the best intentions and the considerable resources of the state government and the federal Superfund hazardous-waste cleanup program, which have spent $ 34 million.

The saga of Stringfellow illustrates the limited capability of government to undo man's abuse of nature. It also spotlights a record of official miscalculation, missed opportunity, mismanagement, bureaucratic inertia and technological timidity, the kind of record that Congress sought to improve with tougher guidelines in the five-year Superfund extension recently enacted.

Although Stringfellow is one of the nation's most dangerously polluted dump sites and one of Superfund's first and best-financed projects since the cleanup effort began in 1981, officials can point to little progress in stopping the 300-foot-wide plume of chemicals that have crept to within 2 miles, or closer, of the Chino Basin.

The frustrations of Stringfellow and other cleanup projects have raised a chorus of criticism among ecologists, community leaders, engineers and members of Congress who had high hopes for the Superfund as the environmental savior of the 1980s.

To these critics, Stringfellow is a symbol of the Superfund's ineffectiveness. As in most other cleanups, they said, officials here have relied for the past five years on shortsighted, stopgap remedies rather than permanent solutions.

As a result, the plume of carcinogenic chemicals has kept advancing and, with it, so has the estimated price of the cleanup, now as high as $ 330 million.

When ground water tests turned up toxic chemicals in Glen Avon's private wells, the Superfund paid to have DDT-laced soil scooped from the site and contaminated liquid sucked out of the ground. Both were transferred to another California dump site, which began leaking in 1984 and now is a candidate for cleanup.

The transfer method, condemned here and elsewhere as the "Superfund shell game," occurred at a third of the 100 sites for which cleanup strategies had been formulated as of late 1985, according to a study by the National Campaign Against Toxic Hazards.

To augment offsite disposal of Stringfellow wastes, the Superfund also paid to have the poisons contained at the site. A clay cap was placed atop the surface to keep rain from seeping into the earth. Fractures in the bedrock underlying the site were sealed with gel to prevent contamination from escaping into the ground water below. An underground clay barrier was erected to wall in the hazardous materials.

But parts of the cap eroded and sank, permitting rain to permeate the ground. The water seepage reactivated and put more pressure on the submerged chemicals, forcing them through unsealed cracks in the bedrock and beyond the site.

This containment strategy, scorned here and at other sites as bandaid therapy, was used at a third of the Superfund sites surveyed by the National Campaign Against Toxic Hazards.

Superfund, whose new $ 9 billion budget represents a fivefold increase over its first five years, has completed cleanups at 13 of the thousands of contaminated U.S. sites. Even that number is disputed by critics who contend that, like Stringfellow, several of the toxic-waste sites have been superficially treated for symptoms rather than for the cause of their ills. Moreover, the program has been faulted for ignoring such new technologies as chemical neutralization in favor of the discredited transfer and containment approaches.

The Environmental Protection Agency, which administers the Superfund, says that so few projects have been completed because of the complexity of most waste sites. At the same time, officials point out that the Superfund has resolved 650 short-term toxic emergencies, such as chemical spills from trucks or leaks from barrels of contamination.

In reauthorizing the Superfund, Congress sided with EPA's critics. The law enacted last month prohibits the Superfund from transferring wastes to other leaking dump sites, and it mandated permanent remedies such as incineration wherever possible.

"We can't keep doing patch and plug," said Penny Newman, a Glen Avon community activist, "and this playing musical chairs with the waste doesn't work. The arguments that Superfund has always put forth is that we have to use proven methods. But the only thing that has been proven is that none of them have worked.

"It's been like sitting in a fire truck and watching a house burn down and doing nothing about it," she said of the government's work at Stringfellow.

Keith Takata, the EPA's Superfund chief for the region encompassing Stringfellow, conceded that cleanup work at the California site has been "slow and expensive" and that "a lot of the steps taken are not the kind of steps we'd take today." But, he said, the long delays have allowed time for study of new technologies, some of which may take 30 years to complete the cleanup.

"Obviously, we can't be as frustrated as the community," he said in an interview. "But in many respects, a lot of us working at EPA feel similarly."

Stringfellow made national headlines in 1983 when congressional critics accused then-EPA Administrator Anne M. Burford of delaying a $ 6 million federal cleanup grant for the site in an effort to prevent then-Gov. Edmund G. (Jerry) Brown Jr., a Democrat, from claiming credit for it. At the time, Brown was running for the U.S. Senate.

The 17-acre dump site ringed by the Jurupa Mountains 50 miles east of Los Angeles has been a local environmental story far longer.

In 1954, the state identified the site, then owned by the Stringfellow family, as an ideal burial ground for toxic wastes. The canyon, named after its pyrite rock, was thought to be undergirded by impermeable bedrock, which would prevent seepage of the chemicals into the deeper ground water.

The site began accepting liquid industrial wastes in 1956. Chemicals were unloaded into 20 deep pits gouged into the steep canyon and were left to evaporate. A spray system was used to quicken the drying process.

For 13 years, Air Force bases and hundreds of the largest U.S. corporations based in southern California, including defense contractors, chemical and oil companies and metal manufacturers, paid the Stringfellows to dump more than 30 million tons of contaminated wastes at the site, according to state and federal officials.

A list of the toxic substances dumped at Stringfellow looks like a chemical alphabet soup. Among probable human carcinogens or mutagens were trichloroethylene (TCE), methylene chloride, chloroform, tetrachloroethylene, cadmium and nickel compounds.

The first environmental portent occurred in early 1969 when heavy rains caused the ponds to overflow and spill into the community a mile downhill of the site. Stringfellow erupted again in the rainy months of 1978, 1979 and 1980, with liquid wastes flooding yards, living rooms and the elementary school grounds. Residents recall how tennis shoes and blue jeans disintegrated in the toxic soup.

"It was like a river, foul and foamy," said John Alexander, remembering the 1978 flood that ran across his property here. "It dried, and the earth was a weird gray like a moonscape."

More ecological trouble was brewing below the surface. The bedrock originally believed to be impermeable turned out to be highly fractured. Rain flushed industrial poisons through it in the same manner boiling water forces coffee through a drip-filter pot. A brownish chemical layer settled in the clean ground water, which is located underground, between 2 and 20 feet deep.

Stringfellow suspended operations after the 1969 deluge, and it finally shut down in 1972 after ground water samples at the Glen Avon school revealed levels of heavy metals and certain chemicals higher than local standards permitted.

The farther from the site officials have tested since then, the farther they have turned up ground water contamination. When some of the private wells of Glen Avon residents were found in 1984 to contain radiation two times higher than the federal drinking water standard, the state began providing bottled water to the community. For 2 1/2 years, 400 families have had to rely on the bottled water for drinking and cooking while still using well water for bathing.

Tests last September traced the chemical plume to a point 8,000 feet from the Stringfellow site, in the center of Glen Avon. TCE levels reached 40 parts per billion there, eight times the state's public health standard.

No one knows how far the plume has migrated or how close it is to the Chino Basin, which lies in the path of the underground chemical stream that is moving in a southwesterly direction. Officials have not yet tested beyond the 8,000-foot marker about two miles short of the basin.

The danger looming for Glen Avon's two neighboring counties that use Chino Basin water has already visited this ranching and blue-collar bedroom community for Orange County and Los Angeles.

For years, Glen Avon's children suffered from what seemed to be an unusually high incidence of rashes, earaches and upper respiratory and urinary problems. There also were stillbirths and birth deformities in cattle, peeling hooves in goats and loss of fur in dogs and cats.

"People started to put things together a couple years after the floods," said Penny Newman, chairman of Glen Avon's Concerned Neighbors in Action. "It took a while to make a connection between the site and the health problems."

At her urging, the state hired the University of California School of Public Health to perform a health survey of Glen Avon. The report released last February found higher rates of the chronic children's illnesses in Glen Avon than in a neighboring town as well as higher rates of skin cancer and angina pectoris.

The study cited "moderate associations" between public health and place of residency, noting that Glen Avon citizens may have been contaminated by inhaling toxic fumes from Stringfellow, drinking chemical-laced ground water or having contact with soil and surface water fouled by the floods.

"We're walking time bombs," said John Alexander's wife, Connie. "Some of this stuff is so insidious, you don't know when you'll have trouble."

For Frank Fionda, the trouble has arrived. A year after he moved his family to Glen Avon in 1981, he began having heart problems diagnosed by his doctors as cardiac arrhythmia. In and out of the hospital for the past four years, he has suffered from depression, memory loss, stomach cramps and overheating.

"I never even had a headache until I moved here," said Fionda, who blames his poor health on water drawn from his private well later found to contain TCE and other toxic chemicals.

The government's response to Stringfellow has been summed up by University of California engineer George Trezak, who has analyzed the site for the federal Office of Technology Assessment, as "low-budget, quick-fix activity" and "technical and economic judgments, which in the long run have proved costly."

Perhaps the costliest was the failure of local officials in 1977 to approve the bid of an engineering firm to remove all contaminated soil and liquids for $ 3.4 million, one-hundreth of the cost estimated for such work today.

The Superfund entered the scene in 1981. Although the program was in its infancy, it placed Stringfellow on its interim priority list and served as adviser and later financier of the containment and transfer schemes implemented by the state.

For three years, 350,000 gallons per month of contaminated fluids were pumped out of the site and taken first to the BKK hazardous waste site about 25 miles from Glen Avon and then to the Casmalia Resources Landfill 250 miles away. BKK was shut down in December 1984 after geologic tests showed that chemicals dumped there were leaking into the ground water. Now, environmental groups contend that the same problem has begun at Casmalia, which each month still receives tons of hazardous heavy metals from Stringfellow, including cadmium, mercury, lead, copper and arsenic.

"Our goal was to stop the flow of contamination into [Glen Avon]," said state Stringfellow project manager Ted Rauh. "The only place we could put it was another hazardous-waste facility. Our design was not to create a problem elsewhere."

The containment effort completed in August 1982 was aimed at confining the underground chemical plume to Stringfellow. After shipping 1,000 cubic yards of contaminated topsoil to the BKK facility, engineers capped the site with clay, dirt and kiln dust to neutralize the acids. The plan was designed to prevent rain from seeping into the ground and adding volume to the contaminated ground water.

But contractors ran out of materials needed to fashion the cap into a convex shape best suited to ward off rain. Instead, the design was concave. As a result, the ground cover trapped rain and eroded, reactivating the chemicals in the ground and allowing more water to descend and push the plume forward.

"It was real Keystone Kops," Newman said. "The community had assurances that this would work, and it didn't even last through the first rainy season."

To stop the plume's migration off site, contractors dug a deep trench at the foot of Stringfellow and walled in the exposed earth with a clay barrier. Where the barrier met bedrock at the bottom of the trench, gel was injected to seal fissures.

Soon, the dam came under pressure from seepage of rain and it sprung leaks. Contaminated ground water resumed its flow through the cracked bedrock.

Trezak, in a 1984 report, said that because of the bedrock fractures, such conventional containment was bound to fail. Anything short of removing all the contaminated liquids and soil, he said, guarantees continued pollution of ground water.

The failure of containment and transfer procedures by early 1983 sent the Superfund back to the drawing board. But a scandal involving Burford paralyzed the program nationwide, and it was not until 1984 that EPA officials began to search for alternatives. New plans were supposed to be finished by late 1985, but the agency postponed its study while internal problems preoccupied the state health department.

The Superfund resumed its study last June. And Takata said the adoption of a new cleanup strategy is expected late next year.

"The main thing is that our investigations and studies are getting better," he said.

Meanwhile, Superfund engineers are extracting water from Stringfellow in the hope of slowing the migration of contaminated ground water. A $ 3.5 million treatment plant cleans the water and sends it through an industrial sewer line, with the residual sludge going to Casmalia.

To Newman, the EPA has been "absolutely negligent" in delaying cleanup of Stringfellow. "They've been slow. They've responded to an emergency with old textbook remedies. They've accomplished nothing.

"Superfund was presented to me as being the answer," she said. "I don't think any of us thought we'd still be here asking the same questions."