For US, edging down the thermostat has paid off

Turmoil in world oil markets should not be allowed to obscure the shining US success story of energy conservation. No single factor, experts agree, contributed more to the decline of OPEC's power and to tumbling oil prices than the decision by Americans to cut back on their wasteful use of oil.

Today the United States burns 20 percent less oil than it did at the peak period four years ago - 21 million barrels per day early in 1979 compared with just over 15 million b.p.d. now.

That translates into nearly 6 million barrels a day saved. If the country had continued to burn, instead of save, that amount, the 13-member Organization of Petroleum Exporting Countries would still be comfortably in the driver's seat , dictating the global price of oil.

US oil imports have gone down 45 percent over the past five years, according to the American Petroleum Institute (API) - from nearly 8.8 million barrels daily in 1977 to 4.8 million b.p.d. in 1982.

From the standpoint of energy security - that is, vulnerability to an oil cutoff - the US position also has greatly improved. Much more oil comes from non-OPEC sources than was the case a few years ago.

Arab nations now provide only 12.4 percent of all crude oil imported by the US, says the API, a striking drop from the 34.7 percent from Arab wells as recently as 1981.

America's chief suppliers of foreign oil currently are Mexico, Canada, Nigeria, and Britain - none of which would participate in an Arab oil embargo, such as caused havoc to US supplies in 1973.

By the fourth quarter of 1982, Saudi Arabia, long the No. 1 supplier to the US, had dropped to fifth place. Last December they sank to eighth place, providing only 237,000 b.p.d. - a fifth of their total a few years ago.

The full scope of the US contribution to world energy conservation can be measured in another way. Today the noncommunist world burns about 46 million b.p.d. of oil, down from 52 million barrels daily in 1979.

That 6 million barrel decline is only slightly more than the daily savings achieved by the US alone.

Now the question is: Will Americans hold onto those gains, as the economy recovers and the price of heating oil and gas drops?

Factories running at 80 percent capacity obviously will burn more fuel than plants operating at 68 percent of capacity, the utilization figure of the past few months.

Clearly, the temptation to drive more miles and use a bit more heat or air conditioning grows, as the price of fuel shrinks.

Nonetheless, some powerful built-in factors militate against a return to the wasteful ways of the past, experts agree.

Cars on US roads, taken as a whole, are much more fuel-efficient than the fleet of a decade ago. Improvement continues as gas guzzlers are replaced by new models. This is ''mandatory conservation,'' required by law.

''Voluntary conservation'' is shown by US government surveys which found that more than half of all American homeowners have reinsulated or otherwise improved the energy efficiency of their dwellings since 1973.

US factories, large and small, have reduced the amount of energy needed to manufacture goods. Oil refiners, the chemical industry, and makers of aluminum, among others, have met or exceeded government targets for energy conservation.

Permanent gains built into the US economic system will remain, no matter at what level oil prices stabilize.

Gasoline prices at the pump, which have fallen roughly 12 cents a gallon since the beginning of the year, will take a slight upward bump when the 5 -cent-a-gallon increase in federal taxes takes effect April 1.

Most dealers, having squeezed their profit margins over the past few months, are expected to pass through to consumers most or all of the 5-cent surcharge.

''I have to pass it along,'' said a suburban Maryland station owner. ''My selling price on regular leaded now is only 2.5 cents a gallon more than I pay my supplier.''

Even a 5-cent-a-gallon increase may cool the ardor of many drivers who had been tempted to drive more miles by the recent free fall of gasoline prices.

The Department of Energy estimates that US demand for oil this year will rise only 0.7 percent above the 1982 level, despite economic recovery and lower oil prices.

Conservation and increased efficiency in the US automobile fleet, says J. Erich Evered, a senior Energy Department official, are major reasons why the consumption increase should be slight.