The discovery of radioactive black ooze seeping from the ground a quarter-mile from the U.S.-owned uranium plant here has buttressed workers' claims of unlicensed dumping of hazardous waste outside the factory fence.

The chance finding of the ooze by plant workers last month led to the uncovering of a burial ground for radioactive debris just north of the Paducah Gaseous Diffusion Plant, federal officials confirmed last week. The waste, barely hidden beneath a thin layer of soil in a grassy lot, came to light when workers noticed a tar-like substance pooling in the tracks made by their truck.

Department of Energy officials fenced off the site and reported the discovery to Kentucky's environmental regulators.

"We're very concerned about any improper disposal of radioactive material," said Mark York of the Kentucky Natural Resources and Environmental Protection Cabinet, which is investigating the incident.

The presence of contaminated material outside the plant appears to corroborate one of the most serious allegations contained in a worker lawsuit filed in June against the plant's former operators: that radioactive material was dumped outside the plant in areas within easy reach of the public.

The finding comes in the second week of an Energy Department investigation at the Paducah plant, which for 47 years produced enriched uranium for nuclear weapons, Navy submarines and commercial power plants. The probe was launched after reports of contamination and sloppy waste management at the plant, including worker exposure to plutonium and other highly radioactive material.

Thousands of tons of contaminated material are known to be buried in trenches or piled in scrap heaps inside the plant's security fence; a key point of contention is whether radioactive material was also dumped outside the plant in violation of state waste permits.

The suit by workers and an environmental group says contaminated debris streamed out of the plant for years. Some was allegedly dumped in woods and abandoned buildings in a state wildlife area. But other waste was trucked to a state-licensed landfill authorized to accept only nonhazardous trash, the suit contends. The landfill, which was closed in 1996, is on federal government property just north of the plant fence.

"If you can kick up black ooze just by driving across a field, it makes you wonder what else is out there," said Joseph Egan, a lawyer representing workers in the suit.

Both the Department of Energy and the plant's current manager, U.S. Enrichment Corp., have contended that they are unaware of any radioactive waste going into the sanitary landfill. Documents prepared by former contractors list the contents of the dump as "uncontaminated trash and garbage." The landfill is "permitted and operated according to Kentucky regulations," according to plant records.

But the discovery of the radioactive black ooze in an area just outside the landfill is sure to add heat to the debate. The ooze was found July 15 by contract workers preparing to install monitoring wells to investigate another possible indication of contamination: radioactive metals in ground water near the dump, discovered last December.

When workers noticed tar-like liquid in one of the tracks left by their drilling truck, they first suspected an oil leak. They dug into the earth and turned up what appeared to be bits of tar paper and asphalt shingles.

"Observations indicated possible roofing debris," an Energy Department report said.

Not until three weeks later, after further excavation at the site, did plant officials learn that material was contaminated. Radioactivity readings were hundreds of times above levels found naturally in soil; they were also nearly nine times higher than the plant's "action level," the limit that triggers immediate steps to seal contaminated areas inside the plant.

Lab tests confirmed the presence of uranium and technetium. Technetium, a radioactive metal that travels quickly through soil, was one of the contaminants brought into the plant inadvertently during the 1950s, '60s and '70s in shipments of recycled uranium from government nuclear reactors used to produce plutonium.

While the tests were underway, plant officials combed through archives for clues about the mysterious dumping. Some records suggested the spot was used as an off-site dumping ground for plant construction debris from the early 1950s to the 1980s.

"We knew it was an area of concern, so it wasn't a total surprise," said Jimmie C. Hodges, the Energy Department's site manager at the plant. He said the buried debris will be further investigated and incorporated into the plant's ongoing cleanup efforts.

The legal implications of the discovery are unclear. Although Kentucky has not issued a formal response, one senior official initially suggested the ooze would be treated as "a release from the sanitary landfill." That would be a de facto admission that the landfill contains radioactive hazards, in violation of the government's permit.

Even though the workers found the ooze a few feet from the landfill, York, the state environmental official, said on Friday the debris "was not part of the landfill." No enforcement action had been taken because the government had promptly reported the waste and was planning to clean it up, he said, adding that further enforcement steps had not been ruled out.

But if the waste was not part of the landfill, it might represent an uncharted and unlicensed radioactive waste dump, said Egan, the attorney. He also expressed skepticism about the government's position that the waste did not come from the landfill.

"It's a sanitary landfill with a ring of radioactive waste around it?" Egan said.

While government officials decide what to do about the discovery, the spot where the ooze was found remained cordoned off last week with plastic chains strung from concrete posts. The mound of red dirt covering the site had been topped off with a scattering of hay.

The contaminated area borders a state wildlife area, which is often traversed by horses and hikers. About a mile downhill from the dump lies a small pond, where on a recent afternoon three fishermen were trying their luck against the local catfish, using chicken livers as bait. A sign at the pond reads, "Notice: All grass carp caught in this lake must be released immediately."

One of the men, Wayne Whitfield, landed a 2-pounder and looked it over for obvious tumors.

"I ain't going to tell you [contamination] hasn't been in the back of my mind," Whitfield drawled as he slipped a fresh piece of liver onto his hook. "I'm waiting until I put one in the refrigerator and it glows."

The latest discovery comes at a time when the plant's neighbors are still recovering from an earlier radioactive scare at a home two miles from the facility.

On Monday, county emergency officials reported that three buried 55-gallon drums discovered behind a couple's West Paducah house were radioactively contaminated, touching off fears that hazards from the plant had spread into a residential neighborhood.

The homeowner, Jim Hutto, was scooping up soil in his yard Monday evening when he uncovered the three barrels a few feet behind his residence. A friend who happens to work at the uranium plant agreed the barrels looked suspicious and called in the Kentucky Department for Environmental Protection. Soon, several government officials were combing through the site.

A county disaster worker produced a radiation monitor, Hutto said, which showed dangerous levels of radiation on Hutto's clothes, on the front steps of his house, on the back of a state inspector's shirt and on an inspector's shoes. The men then walked toward the exposed barrels, holding the monitor ahead of them, Hutto said.

"It just went off, and they started running -- I mean, running," he said.

Federal investigators and plant officials later arrived with more sophisticated equipment. But after hours of tests, they reported no evidence of radiation, except for small amounts on the state worker's shoes. State regulators declared the area a hazardous waste site and launched an investigation into the barrels' origins.

The confusion about radiation dismayed Hutto and his wife, Terri.

"How did it go from a high reading, to nothing? I'm not completely comfortable," she said. "I want someone to prove to me what the truth is."