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ROME, Dec 15th-A new computer-aided report from the conserv ationist Earth Club indicates that without major policy changes a sev ere shortage of oil by the year 2020 will force a drastic fall in production, widespread unemploy ment, soaring inflation, and choking pollution.The report, based on a computer model assuming present patterns of industrial growth, said by the end of the first two decades petroleum will provide only one-third of the world's energy needs.Natural gas production will fall off even more sharply, it said, and most of the world's gas and oil pipelines and refineries will be working at less than 35 percent capacity-further reducing efficiency and increasing waste. Soaring prices will encourage exploitation of difficult- to extract oil and gas deposits, it said. Ev en assuming double current world estimated reserv es, the computer predicted supplies would not come close to meeting world needs. The report said a large increase in the use of coal was the only short-run possibility. But it warned massive use of coal--both clean-burning anthracite and more plentiful, but more polluting-would sharply increase worldwide air pollution with unforeseeable effects on climate and world oxy gen levels.The report was nearly as pessimistic about more exotic energy sources. Solar power, it said,would provide much needed energy inputs, especially for home heating, but was too limited-at least with present technology-for the major power requirements of industry ，transportation, and electrical generation. Wind, geothermal, and hy droelectric power were also useful, the report said, but too limited to have much effect on total energy supplies. The report indicated questions of safety，radioactive waste disposal, and limited supplies of enriched uranium would sev erely retard the growth of nuclear fission power.It predicted the breeder reactor, so called because it produces ("breeds") more fuel than it consumes, could only come into use when worries about its end product- -dangerous, weapons-grade plutonium-could be put to rest. It said the breeder-reactor, whose dev elopment has been halted in the United States for safety reasons, could not possibly be on line before the year 2020 and the predicted energy crunch.The last alternative examined was that of fusion power. The study concluded that even with the best of luck and massive gov ernment spending, fusion would only just be coming into use as the crisis hit-too little and too late to help.The report concluded there was no single answer to the energy crisis. It suggested that a drastically revised "world energy life style" that included much less industrial growth, vigorous energy conserv ation schemes, lower population growth, and much higher use of replenishable energy sources such as solar power- -was the only way to soften, if not avoid, the worst effects of the coming energy shortage.