On a bank of the Delware River, in the hazy shadow of the giant Memorial Bridge, sits a 275-megawatt yo-yo.

It is the Deepwater Generating Station, a power plant that happily powered its turbines almost exclusively with coal for the first 40 years of its existence. Then it fell victim to the great energy zigzag -- a changing federal energy policy that has pressed it to switch fuels four times in the last 12 years:

In 1969, the government told Deepwater the coal it burned was too dirty, so the plant switched to oil.

In 1973, the government said oil was too scarce. The plant changed back to coal.

A year later, the government again decided that clean air mattered more than oil. So the plant dropped coal and went back to oil a second time.

Now, bent on reducing the nation's dependence on imported oil, the government has had another change of mind. Within three years, Deepwater again will burn coal.

"We're victims of circumstance," complains plant superintendent John McCann. "It's rediculous."

Until now, Atlantic Electric, the south Jersey utility that owns Deepwater, had never faced an actual order to switch fuels. But shifting federal policies, in the face of economic considerations, left the utility with little choice.

It all began in the late 1960s, when the age of the environment rolled around, bringing with it reams of tough new pollution regulations: limits on how black smokestack emissions can be and how much grimy ash can fly into the air, restrictions on sulfur in fuel, a chemical that mixes with air to damage lungs, corrode buildings and ruins crops with acid rain.

Rather than spend the millions for special equipment to meet the new rules, Atlantic Electric converted the plant in 1969 to oil, not only light in sulfur and soot, but also then cheap and easily available.

But times changed. The 1973 oil embargo dried up the plant's fuel supply and drove its costs, so when the government temporarily relaxed pollution standards to encourage use of coal, Atlantic Electric jumped at the chance -- which didn't last long.

The Mideast oil choke loosened. Meanwhile, the usually quiet folk of Pennsville Township began to worry about the thick black smoke they saw pouring into the air from the Deepwater stacks. And they began to complain about the fine black dust that floated down onto their cars, homes and everything else.

Atlantic Electric blamed the problem on its use of "junk coal," low-quality stuff full of sand, dirt, clay and balls of sulfur. The utility says the coal industry had nothing else to sell.

But Deepwater's location beside a major access road to New Jersey gave its pollution problems a high profile in a state already troubled with its image of an industrial near-wasteland.

Mortorists entering the state are greeted by a "Welcome to New Jersey" sign, notes Atlantic Electric production vice president Chris Schwemm, "and just to the right of the bridge are our stacks."

So when state officials started citing the plant for violating antipollution standards, the utility took it as a hint that its request to keep burning coal would not get a warm reception from either the state or federal government. By the end of 1974, Deepwater was back on oil.

Now the Department of Energy has told Deepwater -- and dozens of other plants -- to convert again to coal, this time to ease the nation's addiction to expensive foreign oil. The utility has drawn plans to spend $25 million for new antipollution equipment needed to meet air quality standards. Most of the money will pay for a giant filtering "bag house" to trap ash particles that would otherwise fly out the stacks. The $3.6 billion federal "backout" bill, passed June 24 by the Senate to help utilities pay for the conversion to coal, would cover much of the cost if it is enacted.

But while the antipollution equipment won't be ready for three years. Deepwater could switch to coal in less than a month, and Atlantic Electric is eager to move to cheaper coal right away. The utility has petitioned the Environmental Protection Agency for an interim exemption from the air quality rules.

If granted, the exemption would let Deepwater's No. 8 boiler -- the one that would switch to coal -- emit nine times as much sooty particulate matter as air pollution standards allow, according to the utility's own estimates.

Pennsville Mayor Donald W. Sparks says that's too much. "We had the problem before, and we're really not interested in having it again. We just don't want to be polluted, when the technology's here." Sparks says the township will try to keep Deepwater from burning coal without the planned filtering equipment, even if the plant gets an exemption from the EPA.

Atlantic Electric senior vice president Doug Huggard concedes that "if there is an impact to firing coal, it's going to be local." But utility officials say the switch would save its customers $9 million a year -- about $1 on each home's monthly bill.

For Deepwater, coal presents a new and old set of problems that leave Superintendent McCann ater 33 years there, with mixed feelings. It willl require a new work crew to move the coal from small mountais outside onto the conveyors that feed the boilers. It is also a rougher fuel that will cause far more leaks and breakdowns than oil. Says Mccann: "I'm an operator; oil is easier. I'm a customer; coal is better."

Burning coal on boiler 8 -- and two other boilers that provide steam for an adjacent DuPont chemical plant -- wll leave Deepwater with as much as 200 tons of waste ash each day. Atlantic Electric hopes to sell some of the stuff, but will pump the rest out to a planned 10-acre pond in front of the building.

But that is only a short-term solution. "If and when we fill the pond, we'll have to go somewhere else -- and I don't know where," says Howard McIlvaine, a company official helping plan the coal conversion. The most obvious possibility is a landfill. But the plant's ash would require a large site, and potential problems of blowig dust and groundwater contamination suggest such a fill should be in an isolated site -- hard to find in heavily developed New Jersey.

Despite all the hazards, area residents don't seem terribly concerned about Deepwater's move back to coal. A public hearing on the matter last week drew more reporters than concerned citizens.

"Sure, the soot's going to bother people," says John Fue, manager of a lumber store across the street from the Deepwater entrance. "But I'm looking at the lesser of two evils. It's a matter of having people around with black lung or no people at all."