Synthetic fuels might help solve the gasoline problem, but their use would accelerate the carbon dioxide buildup that is threatening to overheat the earth's atmosphere, the Council on Environmental Quality warned yesterday.

In a report to the council, four environmental scientists said the danger from carbon dioxide is such that it should be considered as "an intrinsic" part of any proposed policy on energy."

Large amounts of carbon dioxide are produced in the burning of any carbon fuel, such as oil, gas or coal. In the atmosphere, carbon dioxide absorbs infrared radiation and prevents it from escaping into space, the scientists' report explained. The process is often referrred to as the greenhouse effect.

Although many complex factors affect the climate, it is generally thought that the result of continued carbon dioxide production will be a warming of the atmosphere "that will probably be conspicuous within the next 20 years," the report said. "If the trend is allowed to continue, climatic zones will shift and agriculture will be displaced."

Gordon J. MacDonald, environmental studies professor ad Dartmouth College, who is one of the authors said in an interview that large-scale use of synthetic fuels -- made from coal or oil shale -- could cut the time involved by half.

"We should start seeing the effect in 1990 without synthetic fuels. . . . but if you use them, the effect would be much more pronounced by 1990," he said.

Synthetic fuels produce more carbon dioxide than regular fuel because the amount generated in their manufacture has to be counted as well, MacDonald said. The report estimated that for the same amount of heat, synthetic fuels put out 1.4 times as much carbon dioxide as coal, 1.7 times as much as oil and 2.3 times as much as natural gas.

Synthetic fuels are enjoying a popularity boom on Captiol Hill, where legislation is pending that would boost their production with funding of $2 billion and more.

A Department of Energy environmental impact study of synfuels, not yet made public, notes the high carbon dioxide emissions but does not relate them to the climate question. In fact, the study says there is "no absolute environmentally related constraint" on fuel conversion processes now known. DOE is studying carbon dioxide buildup but not this context.

The relationship to climate is controversial. MacDanold, along with scientists George M. Woodwell, Roger Revelle and C. David Keeling, said in the CEQ study that the warming trend is sure even without synthetic fuels and that it could result in the melting of the west Antarctic ice cap in about 200 years. That would raise the sea level worldwide by about 20 feet, flooding most coastal areas.

Other scientists are more cautious. "We're still not completely sure there is a carbon dioxide problem," said Lester Machta, director of the air resources laboratory at the National Oceanic and Atmospheric Administration. It is known that carbon dioxide is increasing at the rate of 3 to 4 percent per year now and at that rate will double its concentration in the atmosphere by about 2030, he said.

"But we don't know how much gets absorbed into the ocean . . . we're not sure of our climate [computer] models . . . and then if there is a warming maybe it's an advantage," Machta continued. Although the CEQ group and other scientists said world agricultural patterns could be disrupted as the weather changes, Machta noted lengthened in some areas, such as Canada and central Russia.

Scientists agree that if there is a warming trend from carbon dioxide buildup, it could still be reversed if enough of mankind cut back on burning fossil fuels soon enough.

"If we wait to prove that the climate is warming before we take steps to alleviate the carbon dioxide buildup, the effects will be under way and still more difficult to control," the CEQ scientists said.

They recommended that the United States embark on a four-part program: acknowledge the problem and relate it to all future energy decisions; pursue conservation of fossil fuels; choose natural gas or other lowemitting fuels, such as nuclear power or solar energy, over coal or synthetics, and promote extensive reforestation to increase the amount of carbon dioxide taken out of the air by plants.

CEQ acting chairman Gus Speth said the report was "very important and cannot be ignored." He added that the council "takes the carbon dioxide problem very seriously and intends to pursue it."

The CEQ is a three-member commission set up in 1969 to advise the president on environmental problems and to recommend measures to deal with them.