Washington — Stable oil prices - actually a drop when adjusted for inflation - can be expected for three years. That's the forecast from a new government study. As a result, gasoline prices ''will be soft the next couple of years,'' maintains J. Erich Evered, who heads the Energy Information Administration, a branch of the US Energy Department. He cautions that ''you will always have seasonal variations'' in price.
While a petroleum supply bulge is expected to push oil prices down $5 a barrel by 1985 to about $25 in 1982 dollars, other energy prices will not be so well behaved, the government report says.
For example, residential electricity prices will rise about 1 percent a year after adjustment for inflation, according to the Energy Department's new Annual Energy Outlook.
And residential natural gas prices will climb an inflation-adjusted 7.5 percent a year assuming no change in the Natural Gas Policy Act, which sets ceiling prices for some gas. At the moment Congress is at work on new gas pricing legislation.
Energy forecasting is dangerous business since unpredictable events like wars and revolutions can radically alter supplies and thus prices. Changes in consumer behavior can also affect demand and thus price.
The government currently expects that consumers will continue their energy conservation efforts even though some energy prices will be falling in real terms. Average per household energy use is expected to drop at a yearly rate of 1.6 percent through 1990 to 99 million Btu per household by the end of the decade.
''You don't have to have rising prices to have conservation efforts'' continue, Mr. Evered asserts. ''Prices are high enough to make such investments cost effective.''
Conservation was the watchword in 1982, the new government figures show. With a nudge from recession-pinched budgets and help from a relatively warm winter, total energy consumption in 1982 fell for the third year in a row to 70. 9 quadrillion Btu from 74.0 in 1981, or about 4 percent. And petroleum consumption dropped 5 percent to 30.3 quads.
As a result of falling oil demand, oil imports last year plunged to their lowest level in 11 years. Imports as a share of total energy consumption fell to 12.5 percent, the lowest level since 1972. US dependence on members of the Organization of Petroleum Exporting Countries (OPC) was down for the fifth straight year to 13.8 percent of total petroleum consumption.
Meanwhile, the recession was also cutting into the demand for electricity. After growing throughout the 1970s, electricity generation recorded its first annual decrease since World War II with output dropping 2.3 percent.
With demand for energy at depressed levels, producers brought less to market. Energy production fell for the second straight year to 63.3 quadrillion Btu, a decline of about 1.4 percent from production in 1981.
Most of the decline came as less natural gas was produced. Consumers wanted less gas because its price had increased sharply. Further, the winter was warmer than normal in many parts of the country. The wholesale or wellhead price of natural gas rose 22 percent in 1982 to $2.42 per thousand cubic feet.
While gas production fell last year, domestic oil production rose 1.2 percent. And for the first time since 1970, production rose outside Alaska. Mr. Evered says the increased production was a response to favorable prices in effect before OPEC lost much of its market power at the end of 1982.
By the end of 1982, however, oil exploration activity dropped off as prices fell. The price for US crude oil at the wellhead fell 10 percent to $28.54.
Oil companies responded by sending 13.7 percent fewer crews to engage in seismic exploration than in 1981. And the number of rotary drilling rigs in operation dropped by 22 percent to 3,105.
The demand for petroleum will not stay depressed as the economy recovers. The government expects petroleum consumption to rise sharply from 15.3 million barrels a day in 1982 to 18.0 million in 1985 and then to decline to 17.0 million barrels by 1990.
US producers will not be able to meet the increased demand on their own. As a result, there likely will be a significant increase in oil imports from the 1982 level of 4.2 million barrels a day to 7.6 million barrels in 1985.
A key reason demand for petroleum will rise is that utilities and factories will have considerable incentive to switch boiler fuel from natural gas to oil. Under current law, which is subject to change, natural gas prices will rise sharply. For example residential natural gas prices will rise from $4.43 per million Btu in 1981 to $6.65 in 1985 and $8.53 by 1990.
The rising price of gas ''is making oil a more attractive fuel in many cases, '' Mr. Evered says. Total fuel switching is expected to add about 1.5 million barrels a day to the demand for oil by 1990.
At the same time the US is slated to be boosting its oil imports to cope with fuel switching, the nation's coal exports are expected to climb. US coal exports are forecast to climb steadily from 106 million tons in 1982 to 144 million tons in 1990.