In the most exhaustive study it has done, the National Academy of Sciences has concluded that the only choice the United States has to meet electricity demands for the next 30 years is to burn coal and build nuclear power plants.

The academy also concluded that nuclear electricity may be the nation's only choice for a 20-year period beginning in 1990.The academy said that burning coal to generate electricity may have to be cut back in 1990 because coal will be more valuable as a source of synthetic liquid and gas fuels and because the increased burning of coal may put so much carbon dioxide in the atmosphere that it could trigger a change in the climate.

In a 783-page report for the Energy Department that took four years to compile and was two years late and $2 million over budget, the academy drew another conclusion bound to generate as much controversy as the others: unless the deamnd for electricity abates unexpectedly, the United States must continue to develop the fast breeder nuclear reactor that President Carter stopped two years ago.

The academy said that use of a breeder would keep the price of electricity low and extend the domestic supply of uranium for hundreds of thousands of years.

"At relatively high growth rates in demand for electricity, the attractiveness of a breeder is greatest and at the highest growth rates the breeder can be considered a probable necessity," the academy said. "For this reason, this committee recommends continued development of the liquid metal fast breeder reactor, so that it can be deployed early in the next century if necessary."

The academy held out little hope that solar power and fusion power would make much of a contribution to the nation's energy in the next 30 years but said the country should continue to support their development.

"Because of the higher economic costs, solar technologies will probably not contribute much more than 5 percent to energy supply in this century unless there is massive government intervention to penalize the use of nonrenewable fuels," the academy said. "The danger of such intervention lies in the possibility that it may lock us into obsolete and expensive technologies with high materials and resource requirements."

On the outlook for fusion, a process that mimics the limitless energy of the sun, the academy was cautiously optimistic -- but not for any time in the next 30 years.

"It is not an option that can be counted on within the time frame of the study," the academy said, referring to 1985 to 2010. "Nevertheless, fusion warrants sufficients technical effort to enable a realistic assessment by the early part of the next century of its long-term promise in competition with breeder reactors and solar energy technologies."

The academy identified as the nation's two most serious near-term needs the necessity to conserve energy and develop synthetic fuels to replace the world's dwindling supply of liquid fossil fuels.

"The most critical near-term problem in energy supply for this country is fluid fuels," the academy said. "Nest to deamnd growth reduction, highest priority should be given to the development of a domestic synthetic fuels industry, for both liquids and gas."

Bearing down on what it said was an inevitable worldwide shortage of oil and natural gas in the next decade, the academy said the nation must begin to rely more on coal and nuclear power for its electricity.

"Coal and nuclear power are the only economic alternatives for large scale application in the remainder of this century," the academy said. "After 1990, coal will be increasingly required for the production of synthetic fuels so the requirements for nuclear capacity depend on the growth rate for electricity demand."

The academy conceded there were serious public risks in generating electricity from coal and uranium. It identified the worst from coal as the danger to the miner and the worst risk from uranium as the threat of nuclear weapons spread.

"The problem of nuclear weapons proliferation is real and is probably the most serious potentially catastrophic problem associated with nuclear power," the academy said. "However, there is no technical fix -- even the stopping of nuclear power (especially by a single nation) -- that averts the nuclear proliferation problem.

"At best, the danger can be delayed while better control insittutions are put in place," the academy went on. "There is a wide difference of opinion about which represents the greater threat to peace: the dangers of proliferation associated with the replacment of fossil resources by nuclear energy or the exacerbation of internatioanl competition for fossil fuels that could occur in the absence of an adequate worldwide nuclear power program."

The academy said that despite the risk of proliferation, nuclear-generated electricity represents the best option for the next 30 years. It said that nuclear electricity is still the cheapest form, is less sensitive to increases in fuel prices and to changes in environmental standards than coal.

"Nuclear fuel supplies are more readily stockpiled than coal," the academy went on, "and nuclear electricity is thus less subject to interruption by strikes, bad weather, and transportation disruptions."

The academy made a final point favoring nuclear energy over coal. It said that if the effect of carbon dioxide accumulation on climate becomes a major environmental issue in the early years of the 21st century, "it will be aggravated by commitments to the use of coal, because power plants have lives of 30 to 40 years."