Oil pollution in the ocean and along the coasts is a nuisance, but there is not much hard evidence that spills have any long-term effect on marine or plant life, oil experts here say.

Nor is oil pollution a human health hazard, as far as scientists have been ablt to determine, add representatives of industry, ACADEME and the Environmental Protection Agency at a conference on oil pollution.

"I've never heard of a permanently crippled environment because of an oil spill," said Kenneth Biglane, the chief oil-spill expert. But EPA is sponsoring expensive research because, he said, "we don't know the full effect of oil on the environment, and so long as there's any doubt, the public is concerned."

Science may never provide an absolute answer. But as more than a dozen papers presented here this week show, evidence is mounting from government, industry and university research that nature is absorbing oil spills with little trauma.

On Feb. 2, 1976, a barge sunk at the mouth of the Potomac, spilling 250,000 gallons of sticky black oil into Chesapeake Bay. Beaches and marshes were fouled, thousands of birds were killed and Virginia officials predicted dire consequences for the area's shellfish industry.

However, after a six-week cleanup, the beaches were virtually free of oil. In a few months the marsh grass had grown back thicker than before. And, after an eight-month study, the Virginia Institute of Marine Science found no effects on mussels and oysters.

The case of the Chesapeake Bay spill, reported at a conference of oil-spill experts here, is not unusual. Despite public outcry over a rash of recent tanker accidents, the danger of oil spills appears to have been exaggerated.

When James N. Butler, a Harvard chemistry professor, started oil-pollution research six years ago, he recalled. "Jacques Cousteau [the explorer] was saying that the oceans were dying and I was fairly alarmed. But the longer I've been in the business, the less true that seems to be."

Butler studied tar lumps from oil tanker discharges in the central Atlantic and found no discernable effect on ocean plants or animals. Other scientists, under contract from the American Petroleum Institute, an industry group, compared marine organisms on Bermuda's tar-polluted beaches and clean beaches, and found virtually no difference in popuplation or reproduction, according to a paper presented here.

"Cosmetics is what gets media attention" in an oil spill, said Charles C. Dates, the Coast Guard's chief scientist. After a 1969 off-shore well blow out near Santa Barbara "kids tracked oil into white carpets. The boats got messed up. It's a headache.

But the uproar over the blowout ignored the fact that millions of gallons of oil have sepped naturally into the ocean off Santa Barbara for centuries. University of Southern California researches reported here that marine organisms live and breathe well around the natural seeps, where there is more oil than that around industrial rigs.

Oil is not a single substance, but a blend of thousands of compounds, experts here point out. Crude oil, as it spouts from the ground, varies from well to win. Different kinds of oil, depending on their composition, have vastly different environmental effects.

Of refined oils, No. 6, a heavy fuel used for industrial boilers, is considered among the least toxic. No. 6 was the oil spilled from the Chesapeake Bay barge and from the Argo Merchant tanker off nantucket, Mass, in December.

Despite predictions of ecological catastrophe, the Argo Merchant oil was washed out to sea without any apparent efeects on New England fish, according to Coast Guard Adm. A. F. Fugaro,

However, No. 2 oil, a lighter homeheating fuel, can poison marine life if it is spilled in a confined area, as 100,000 gallons were off Falmouth, MAss., in a 1969 barge accident.

Today, oil persists in a 10 acre marsh, according to John W. Farrington, a marine chemist at Woods Hole Oceanographic Institute, in Massachussets, and several shell fish beds are still closed. However, he said, no evidence exists that eating the shellfish would hurt people.

"We've tried to get dostors to tell us what are the acceptable levels (of oil), But not one knows" he said.

Farrigton, said studies show that No. 2 oil reduces the ability of certain mussels to eat and grow, and that oil can kill marine larvae. But he added that other research show some organisms break down in their systems, others discharge it once they are placed in clean water, and unlike some pesticides, oil does not move up the food chain in higher concentrations.

"You're not going to get a body count from oil spills," he said. "I'm not saying they're okay - we need to know more.There may be a little risk, but it might no be as dangerous as driving a car.

Although public attention has focused on tanker spills, the National Academy of Sciences estimates that marine transportation accounts for only third of the 6.1 million tons of oil that enter the oceans yeraly. About 25 per cent comes from river runoff - much of that being automobile crankcase oil washing into sewers from gas station. Natural seeps and rainfall, which captures air pollution, account for 10 per cent each.

Of marine transportation pollution a small portion - 15 per cent comes from accidents like the Argo Merchant. The rest is from routine tanker cleaning, deballasting and bilge-pupmping.