Whatever damage the run-up in oil prices inflicts on the economy as a whole, the effect on electricity bills is likely to be relatively modest. Of the fuel-consuming industries, the electric utilities have been the most successful in learning the lessons of the first two oil shocks, in the 1970's, and finding other sources.
Oil accounted for about 16 percent of the fuel used by utilities at the time of the Iranian revolution in 1979, but amounted to only an average of 5.7 percent last year, despite a vast increase in the amount of electricity generated over the last decade. Moving the electric system off oil is important because a growing share of the energy used in this country - almost 36 percent last year - is turned into electricity before it is consumed.
But the amount of oil used by utilities still varies widely from company to company, so the effect of rising oil prices on consumer bills will also vary. The Hawaiian Electric Company, for example, is nearly all oil-powered. The Long Island Lighting Company is still 63 percent oil-dependent, while the Consolidated Edison Company of New York depends on oil to generate 41 percent of its power.
A barrel of oil produces about 500 kilowatt-hours when burned. The average household uses about 500 kilowatt-hours a month. If a utility was 100 percent oil-dependent, a $20 increase in the price of a barrel of oil would raise the monthly electric bill by the same amount.
But most utilities that were heavily dependent on oil in the 1970's have weaned themselves away by converting to coal or natural gas and by purchasing or building hydroelectric capacity or nuclear reactors. In addition, experts say, few plants built in the last few years use oil.
''As the utilities began to see themselves as competitors, and wanted to portray themselves as low-cost producers, the incentives were for them to switch away from oil,'' said Marie Corio, president of Applied Economic Research in New York.
They accomplished this first by running their own plants in a different pattern. They used gas- or coal-fired generation first, bought power from utilities with extra coal-fired capacity next, and then rebuilt their hardware to burn fuels other than oil. This required adding anti-pollution equipment in many cases, although the biggest technical difficulty was often finding a place to store the additional coal, some experts said.
As various users now substitute gas for oil, the price of gas will rise, Dr. Corio said. This may discourage the plans of some utilities and independent power producers to build new natural gas-fired power stations.
Others are not sure the price of gas will rise. ''We don't see a very direct linkage,'' said I. C. Bupp, a managing director of Cambridge Energy Research Associates. Even if oil gives up part of the market to gas, ''there will still be gas-on-gas competition,'' he said.
Coal prices will not rise, because ''there is so much spare capacity, nobody has to dig a new mine,'' said Standley H. Hoch, chairman and chief executive of General Public Utilities in New Jersey. It gets about 45 percent of its energy from coal.
Companies with excess capacity to burn coal will be in a strong position to sell power to those that use oil, said Charles B. Earle and Gary R. Licht, utility analysts at Mabon, Nugent & Company, the securities firm. They add that companies that still use oil heavily may find that after they have passed increased fuel costs to their customers, they will run into political resistance to unrelated increases. Eastern Utilities Associates, which wholesales power in New England, is in the former category, they said. Central Maine Power and Con Edison are among the latter. Still, the public's resistance to nuclear power and the emissions problems that arise from burning coal make it doubtful that oil will disappear in electric generation.
In addition, many utilities and independent power producers have added turbines that burn natural gas when it is available and light oil when it is not. In the Northeast, these generators have been blamed for increasing the demand for heating oil on the coldest winter days, when natural gas is in short supply, as happened last December.
Over all, however, the conversion away from oil has been dramatic.
United Illuminating, which serves the New Haven and Bridgeport areas of Connecticut, is now about 22 percent oil-dependent, down from 92 percent at the time of the Iranian revolution. That figure will fall to 11 percent by 1991, the company says, at which point, even if oil prices doubled, electric costs would go up only 9 percent.
The reasons for the switch by utilities around the country are illustrated by United Illuminating's cost structure. The fuel and operating cost per kilowatt-hour at the plant gate is 2.176 cents for Bridgeport Harbor 3, a 25-year-old plant that was converted from oil to coal in 1985. A less-efficient oil-fired plant, which was used only about 7 percent of the time last year, has a price of 5.3 cents per kilowatt-hour.
United Illuminating and many other utilities also substituted uranium for oil by building nuclear plants, which last year generated 19 percent of the domestically produced electricity, up from 4.5 percent in 1973, at the time of the first oil shock. The Seabrook nuclear plant, which went into commercial operation earlier this week and of which United Illuminating owns 17.5 percent, costs the company 1.792 cents a kilowatt-hour, the utility said.
But building new nuclear plants is an option now closed, for all practical purposes, because of waste disposal problems, safety and regulatory questions, and especially cost overruns. Building Seabrook bankrupted the biggest investor, the Public Service Company of New Hampshire and required United Illuminating to seek several emergency rate increases.
Even when oil bottomed out at around $10 a barrel in 1986, he said, the coal the company was burning in converted plants was cheaper.
Florida Power and Light, which was 53 percent dependent on oil in 1979, completed two new nuclear plants and is now seeking other ways to curtail its oil use. It has signed long-term contracts for natural gas, and recently signed a letter of intent to buy a minority interest in a coal-fired plant in Georgia. This year, oil will make up 22 percent of its fuel, said Michael R. Bumgardner, a spokesman.
Southern California Edison was more than 40 percent dependent on oil at the time of the 1973 oil shock, said Larry Papay, a senior vice president. Now it is 4 to 5 percent dependent on the fuel. In the last 10 years, nuclear power has grown to 17 percent, from 4 percent, he said. The company also burns more coal and natural gas, and buys or generates power from solar plants, geothermal plants and windmills.
The company's focus is on improving efficiency, he said. ''Although conservation lost some of its glamour after 1985, we have continued spending $44 million or $45 million a year'' to help customers use electricity more efficiently, he said. Earlier this year, after negotiations with environmental groups and others, it raised the sum to $75 million, and will increase it again to $100 million.
Less successful in reducing imported oil is Long Island Lighting, which built a nuclear plant that would have displaced more than eight million barrels of oil a year if it had operated as its designers said it would. But the plant was abandoned by agreement with New York State because of safety concerns.
In the last 12 months, the company has been 62.5 percent dependent on oil, 13.5 percent on natural gas, 5.5 percent on nuclear power from a plant upstate and 18.5 percent on purchased power - a mix of natural gas, coal, hydroelectric power and even garbage, which is burned in a power-generating incinerator.
In July, Lilco paid an average of $15.19 a barrel for the heavy oil it uses, up from $14.49 in June. On Monday, it paid $22.50.