Contrary to what one might expect, a major snowstorm like yesterday's causes an overall decline in the energy demand of most big cities.

Those who produce, dispense and watch over our energy resources agree that many factors are involved and that they vary from city to city and from storm to storm. The central fact, however, is that more people than usual stay home when the snow hits. Especially when it hits, as this one did, on a Friday.

"The net impact is that (energy) demand decreases," said Rue Dann of the Department of Energy's press department. "Nobody comes to work . . . there is a decreased demand for fuels in general if industries are closed."

"Residential demand might increase," said Mike Segal of the Edison Electric Institute, the electric utility trade organization. "People are watching TV instead of being at a work-bench. But industrial plants and commercial institutions might be closed down. The variables are such things as how intense the snow is, how cold it is, how long it lasts and the kind of area it is."

Washington, with little industry, shows less visible energy demand reduction than other areas might, said Gayle Butler of the Potomac Electric Power Co. School and federal government closures tend to shift the demand for power to the suburban bedroom communities, she said.

"Snow is essentially an insulator that holds heat in a house," said Paul Young of Washington Gas Light Co. "It forms a shield against the wind . . . our use varies with the degree of cold, really." The area used 707 million cubic feet of natural gas on Thursday, a clear, cold day, and 710 million cubic feet during yesterday's storm, he said. On Jan. 8 and 9, with temperatures in the 20s, the area used 829 million cubic feet and 860 million cubic feet respectively, he said.

Electricity demand hit a new winter peak on Jan. 10 Butler said, when Pepco recorded 2,682 megawatts of power used on a day the temperature averaged 20 degrees.

"Gasoline use goes down pretty dramatically during a storm, in direct ratio to the inches of snow," said Bryce Cecil, marketing director of the Amercian Petroleum Institute. "When airports are socked in there's a dramatic short-term drop in jet fuel use, of course, but only a little drop in diesel fuel demand - the trucks have to keep moving."

It depends, in short, on temperature drops rather than sheer snowfall. "If a business is heating with gas or electricity and closes down, you save a lot more (energy) than if it's heating with oil," explained Ed Morgan, vice president for fuel oil of the National Oil Jobbers Council. "You get 70 to 85 per cent efficiency if you burn fuel oil at home but only 30 to 31 per cent if it's burned to make electricity and then send to you."

Herb Foster of the National Coal Institute said two thirds of all U. S. coal consumption is by utility and industry and tends to fall off during mild-temperature snowstorms. "Our own building is heated electrically," he said. "We hire Pepco to burn the coal for us."