MORGAN CITY, La.— Radium from the earth's crust has been brought to the surface in decades of oil drilling, causing widespread radioactive contamination of the nation's oilfields.

The problem is only now being examined by the oil industry and the Federal Government, which has no regulations to deal with oilfield radiation.

A naturally occurring radioactive material, radium has been found in every oil-producing region in the country, from Alaska to Florida, causing low levels of radiation in pumps, pipes and storage tanks. The radium leaches from mineral deposits into water that comes to the surface with oil. Worst in the South

But the contamination is worst in the South and along the Gulf Coast, where radium concentrations in the water are much higher than in other regions. Compounding the problem in the South is that for years oil companies routinely poured billions of gallons of the water into thousands of unlined ponds before pumping it back into the ground or releasing it into wetlands.

"When I got here in 1988, this radium contamination in the oilfields was the only environmental problem that I had never heard about," said Dr. Paul Templet, the Secretary of the Louisiana Department of Environmental Quality. "At first I didn't believe it. But we investigated it, found out it was true and now it's our newest environmental problem."

The oil industry, he added, "can no longer use the environment as a free disposal system." Questions About Health Risk

State environmental officials do not know the extent of the health risk to oil workers who handle drilling equipment contaminated by radium or to people exposed to radium-contaminated water and soil. But they are worried that exposure to radium raises the risks of cancer and other illnesses. The oil industry contends that the risk is minimal or virtually nonexistent.

Tests of wells in Louisiana and other Southern states have found that the oil-water mixture pumped to the surface contains radiation levels 5 to 30 times higher than the Government allows to be released from nuclear power plants. In contrast to the heavily regulated nuclear power industry, where emissions are strictly controlled and workers heavily protected, radiation in the oil industry has been wholly uncontrolled.

Tests this year on four ponds, or oil pits, in Louisiana found that three of them contained radium concentrations in the soil at least as high as those found at abandoned uranium mills in the West and old nuclear weapons plants in the Midwest and East. The Government is now spending billions of dollars to clean up these mills and weapons plants, and experts suggest that if the Government holds the oil industry to the same standards of safety, the costs of cleaning up oilfield radiation could also reach into the billions of dollars.

Buck Steingraber, a geologist for the Mobil Oil Corporation and chairman of a committee at the American Petroleum Institute that is studying the radium issue, said: "I do not believe the oil and gas industry is going to shirk their responsiblity for cleanup where it's necessary. The question of cost is going to be determined by the standards of safety that are set by regulators." Abandoned Oil Pits

Louisiana officials do not know how many oil pits exist, but most are in the marshes in the southern part of the state or in the pine forests of the north. Many have been abandoned by their owners and are seldom fenced off to keep people or animals away.

Scientists consider the oil pits to be biological dead zones, where no vegetation or wildlife can exist. Officials say the greatest health threats from the pits come from airborne radium dust or from radon, a colorless, ordorless radioactive gas produced from the natural decay of radium. Environmental officials are concerned that if the pits are filled in and homes and businesses built are built over them, the buildings could be contaminated by radon, which has been shown to be a cause of lung cancer.

"There are 70,000 active wells and 120,000 inactive wells in the state of Louisiana," said Glenn Miller, Administrator of Radiation Protection Division at the Louisiana Department of Environmental Quality. "We don't know how many of them could be contaminated. This problem has been out there for years and nobody wanted to talk about it."

Outside the South, particularly in California, Pennsylvania and Alaska, the use of oil pits was prohibited or stopped early in the development of the industry because the excess water contains high concentrations of salt and toxic oil-based chemicals. In these states the contaminated water is pumped back into the ground.

But in the southern oil states like Texas, the industry has operated for most of its history with virtually no environmental controls. This has been especially true here in Louisiana, which is only now trying to address the situation. It has adopted new regulations requiring oil companies to close oil pits by 1993 and is about to propose regulations to require companies to halt discharges of the contaminated water into wetlands and bays. Other Southern states are also considering environmental measures.

The Environmental Protection Agency is conducting its own study of the problem.

Although the oil industry acknowledges that it has known for at least 50 years that radium is present in water pumped up with oil, uncontrolled contamination from radium was not seen as an important health and environmental issue until April 1986, when an oilfield worker found radioactive pipes in a well in Mississippi. Pipes Used on Playgrounds

An investigation of the problem revealed contamination not only in the field but also in the yards where the pipes were cleaned and in nearly 30 schools around the state where old oilfield pipes were used in playground equipment, railings and awning supports. The old pipes were also used to train welders in some of Mississippi's vocational-technical cla****.

One pipe cleaning yard found to be contaminated was in Laurel, Miss. The Shell Oil Company and Chevron USA Inc., two of the yard's biggest clients, paid a total of $100,000 to dig up the soil and haul it to Chevron's uranium mill in Texas. The yard's owners and former workers have filed suit against Shell and Chevron, asserting that the companies were negligent in not issuing warnings about radiation in the pipes. One of the suits is scheduled to be tried in March in Federal District Court in Hattiesburg, Miss.

Radium has been recognized since the early decades of the 20th century as one of the most toxic radioactive substances. It is most dangerous when particles are inhaled or swallowed. Radium emits alpha and gamma radiation, and once the particles are lodged in tissue, they bombard surrounding cells with damaging radiation that can disrupt the biochemical processes that control growth and reproduction. Can Cause Cancer

In the 1920's, scientists discovered that exposure to high concentrations of radium caused lung and bone cancer and other severe bone diseases in workers in New Jersey who painted luminous dials on watches with paint made from radium. More recent studies of residents in Iowa, North Carolina and Florida who were exposed to much lower concentrations of radium in drinking water pumped from wells found that the rates for birth defects and some forms of cancer were above national averages.

The discovery of extensive radium contamination in the oil industry has provoked a new debate over the health threats from exposure to low levels of naturally occurring radioactive materials.

The American Petroleum Institute, an oil industry trade group, has begun a study to look at the health risks to pipeyard workers and to the public.

The institute conducted one study last year that showed that 99 percent of all oil equipment tested across the country produced less than 2 millirem per hour of gamma radation, the level at which the Occupational Safety and Health Administration requires companies to protect their workers.

But state officials across the South have found old pipes and equipment, some used in public buildings, that emit radiation levels as high as 8 millirem per hour. If someone stood close to thes pipes for four hours they would receive as much radiation as one bone X-ray.

Tests by the Louisiana Department of Environmental Quality have attempted to a****s the threat from contaminated oil pits. In one pit southeast of Houma and east of Morgan City, the department found radium readings as high as 533 picocuries per gram in the soil. Natural background radium in Louisiana's soils and sediments range from 4 to 8 picocuries per gram.

The high radium levels found in the pit are comparable to those found at the nuclear weapons production plants and uranium mills around the country, which are now being cleaned up by the Energy Department. The department considers radium levels in soil at its plants safe if they are 5 picocuries per gram or less.

Experts suggest that the greatest potential threat to workers in the oil industry comes from cleaning radium-contaminated debris from drilling equipment. Just as dirt acc**ulates inside a kitchen drain pipe, sludges containing radium collect on the inside of oil drilling pipes and on the bottom of tanks. The sludge forms rust that is radioactive enough to be classified as low-level nuclear waste. Contaminated Dust in Air

When the pipes are cleaned, radium-contaminated dust fills the air and can be inhaled or swallowed. At a pipe cleaning yard in Lafayette, Louisiana's radiation inspectors discovered radium levels high enough that an employee working full time in the area could absorb more radiation than the average nuclear industry worker.

Last year, Louisiana became the first state to require pipe cleaning companies to protect workers with masks.

Here in Morgan City, 90 miles southwest of New Orleans a center for Louisiana's offshore oil activity the Shell Oil Company has stirred protests with a plan to dispose of radioactive oilfield wastes by pumping them back down an abandoned well 40 miles offshore, near Eugene Island.

Shell is storing pipe-cleaning wastes in more than 1,600 barrels at an industrial yard here near the center of town. Shell executives said they planned to build a processing plant to mix the pipe rust with drilling mud. That mix would then be shipped to the abandoned well and pumped back into the ground.

They say disposing the wastes in abandoned wells is safer and less expensive than shipping and storing the wastes, at a cost of $300 to $500 a barrel, at a site in the desert 80 miles west of Salt Lake City. The site is the nation's only repository for storing naturally occurring radioactive materials. Three other sites, in Washington State, Nevada and South Carolina, are licensed to accept the waste but have discouraged it, saying the waste would take up too much room.

The proposal to use the abandoned wells has gained support from the Department of the Interior, but some Morgan City residents say they are concerned that if Shell's proposal is approved by the state and Federal governments, Morgan City could become the center for processing radioactive wastes for disposal offshore.

"We're just finding out about this now, and it's got us nervous," said Merlin Price Sr., a Morgan City resident and a law-enforcement officer in St. Mary Parish. "They say it's going to be safe, but nothing has been proven. It's the first time anything like this has been done in Louisiana and it's all happened very quietly."