A group of scientists, warning of potential ecological imbalances and climatic changes, yesterday urged the government to slow its pursuit of a large-scale synthetic fuels program.

The scientists said the ecological changes could result from higher levels of carbon dioxide in the atmosphere -- one assured by product of a switch to synfuel production.

They described the so-called "greenhouse effect" whereby heat is trapped close to the earth by increased levels of carbon dioxide, and predicted some long-term effects might be erratic world food production, severe droughts in some regions and costal flooding in others.

If temperature levels rose by five degrees in the West Antarctic region, "ice shelves there might break apart, cutting loose the ice they hold up and eventually raising sea levels by about 15 feet," claimed climatic specialist Stephen Schneider, of the National Center for Atmospheric Research in Boulder, Colo.

In a symposium before the Senate Governmental Affairs Committee, the scientists urged President Carter and Congress to diversify federal investments in future energy sources, paying more attention to renewable resources than to fossil fuels.

"There is no way I'd spend $88 billion on synfuels -- $8 billion would be more reasonable. The money should be spread across the board, with more attention to wind and solar power and making nuclear power more safe," Schnedier said.

"Synfuels" are liquid fuels derived from coal, shale and plants. Their proposed production is a major component of the presidents energy plan. Schneider said yesterday that production and use of synfuels would release two to three times as much carbon dioxide into the air as would direct use of coal, because of the energy involved in extracting the liquid fuel.

According to the scientists, this would increase only by only 2 percent the 17 billion tons of carbon dioxide emitted into the air each year from the burning of coal, oil and natural gas. But the contemplated synfuels program would constitue the "single largest source" of carbon dioxide emissions, and thus should be a prime target for government concern, said ecosystem specialist George Woodwell of the Woods Hole Oceanographic Institue.

Schneider said the greenhouse effect is a relatively new idea -- whether the earth is truly warming up will not be discernible for a generation. But since high caron dioxide levels are practically irreversible, "you just can't wait until then to decide you have a problem," Schneider added.

By the year 2000, "if synthetic fuels investment and infrastructure are in place, it will be estraordinarily costly in economic and social terms to move away from a synthetic-fuel economy," according to scientist Gordon MacDonald, to Dartmouth College, a former member of the Council on Environmental Quality.

Experts also voiced concern about the international implications of a U.S. synfuels program. Unless a global agreement is reached on future energy sources, less developed countries will probably choose to develop large-scale synfuels programs of their own, favoring cheap energy and economic growth over less immediate environmental concerns, they said.