If industrial nations continue to burn oil and coal for energy, the world's average temperature could increase more than 6 degrees centigrade in the next 200 years, the National Academy of Science warns.

Such an increase could have "adverse, perhaps even catastrophic" effects around the world, including dramatic changes in agricultural areas and ocean fisheries and a rise in sea level that could flood coastal cities, the academy said in a study released today.

Twenty-three scientists, among the nation's foremost experts in climate and geophysics, participated in the academy's 2 1/2-year study. They concluded that continued reliance on fossil fuels could result in a four- to eightfold increase of carbon dioxide in the earth's atmosphere.

A transparent gas given off when coal, oil and other fuels are burned, carbon dioxide acts like a greenhouse to impede radiation of the earth's heat into space.

While scientists have long debated the greenhouse effect, the academy study is the first major federally sponsored report to take a position on the issue using specific figures.

The findings, while recognizing many uncertainties, indicate that "a reassessment of global energy policy must be started promptly because long before [200 years from now] there will have been major climatic impacts all over the world," the study says.

A comprehensive worldwide research program costing $20 million to $100 million a year, and a national climatic council to coordinate studies on the carbon cycle, climate, population, energy demand and food production should be established, the academy said.

"Worldwide industrial civilization may face a major decision over the next few decades - whether to continue reliance on fossil fuels as principal sources of energy or to invent the research engineering effort, and the capital, that will make it possible to substitute other energy sources for fossil fuels within the next 50 years," the study said.

"A decision that must be made 50 years from now ordinarily would not be of much social or political concern today, but the development of the scientific and technical bases for this decision will require several decades of lead time and an unprecedented effort . . .

"If the decision is postponed until the impact of man-made climate changes has been felt, then, for all practical purposes, the die will already have been cast," the report said, noting that the carbon dioxie would take 1,000 years to disperse.

Carbon dioxide in the atmosphere has increased 11.5 per cent to 13.5 per cent since the Industrial Revolution began, and will have increased 25 per cent by the year 2000, the scientists estimated. They predict it will double by 2050.

About 40 per cent of the carbon dioxide from fuel burning remains in the atmosphere. The rest is absorbed by the ocean, trees and organic matter in the soil, the scientists said, adding that the rapid clearing of forests for farming exacerbates the carbon dioxide problem.

The study avoids discussion of replacements for oil and coal except to say, "No energy sources alternative to fossil fuels are currently satisfactory for universal use."

At a news conference Friday, Philip H. Abelson of the Carnegie Institute, co-chairman of the study committee, said nuclear energy involves other risks, while solar energy is impractical and costly. "One alternative is to conserve," he said.

The study assumes that world population will grow to 10.7 billion by the year 2075 and total energy consumption will increase to 5 times the current level.

Because so much remains to be learned about climate, Harvard Prof. Roger Revelle, head of the energy and climate panel which reviewed the study, said its conclusions were "very shaky." But he added, "They should be taken seriously, because a change in temperature could have profoundly disruptive effects."

Asked if the Carter administration's push to burn more coal is a mistake, Revelle said, "For the next 20 to 30 years, it is all right to use coal, provided we don't get committed to it. But we'll have to be able to kick the habit in the next century if the climatic effects turn out to be deleterious. We should look for alternatives as fast as we can."

Thomas F. Malone of the Holcomb Research Institute, co-chairman of the study committee, said, "This is a flashing yellow light to administration policy. We have to determine whether it will mean a flashing red light or a flashing green light."

The predicted 6-degree centigrade (11 degrees fahrenheit) increase "would exceed by far the temperature fluctuations of the past several thousand years," the study said, adding that "it would be comparable to the difference in temperature between the present and the warm Mesozoic climate of 70 million to 100 million years ago."

Since the Mesozoic era, the world has experienced a gradual cooling, leading to the present glacial age which began a million years ago and is characterized by ice ages relieved by warmer periods. The most recent ice age, during which average temperatures were 5 to 10 degrees centigrade below the present, ended 10,000 years ago, the study said.

To illustrate the magnitude of a 6-degree change, Malone pointed out that during the year 1816, when the temperature dropped an average of 15 degrees, snow fell every month in New England.

A 6-degree increase could mean that the corn belt would move north to Canada, the study predicts. "This wouldn't be so bad worldwide," Revelle said, "but it would be hard on the people in Iowa. Also, the soils in Canada are very poor, while Iowa soil is very good."

Rainfall would increase around the world, but so would evaporation, studies said, thus reducing any benefit from increased moisture. Arid regions, such as the southwest United States, would expand or contract, possibly making large areas unfit for farming or pastures and damaging soil and ground water.

Such drastic shifts in the location of climatic regions, changes in the relationships of temperature, evaporation, water supply, cloudiness and radiation balance would have serious effect on farming technology, cropping patterns and varieties - all based on years of experience, the academy predicted.

Food producting in underdeveloped countries could be severely affected, the study found.

A warmer atmosphere would mean a warming of the upper layers of the oceans, the melting of sea ice and a rise of about 1 meter in sea level, the study says. Fish populations would drift toward the poles and because warm water would form a lid over deep waters, inhibiting natural stirring of the oceans, marine plants would be less productive.