Dig a deep hole in the ground and fill it full of air and presto, you get electricity. That's a vastly oversimplified description of yet another possible energy source, one that could some day help supply Washington's energy needs.

Utilities across the country are investigating such offbeat ideas and resting assorted ways to encourage conservation at the same time as they explore new ways of billing and monitoring home energy use. It's all a part of the looming energy crisis and the way it translates into higher costs for everyone, consumers and power companies alike.

As part of the industry effort to derail federal rate regulation, which is up for consideration today in the Senate as part of President Carter's energy bill, utility executives from eight states told a press conference yesterday what they were doing along these experimental lines.

Much of the industry effort is directed toward trying to spread out demand during the day. From 11 a.m. to 7 p.m. on weekdays, most utilities operate nearly everything they have in order to keep office lights burning, industry rolling and home appliances humming.

"Conservation during peak hours means I can cut back my most inefficient plants (of power generation) and that means overall costs per unit (of electricity used) go down," said Homer Vick of Wisconsin Power & Light.

The idea of filling a hole in the ground with air is one of attacking this problem. Compressed air would be pumped down into an underground cavern during low demand periods, such as the wee hours of the morning, and then released to drive electric generators during peak demand daytime hours. The idea would be to provide another energy source during those hours without having to build a coal or gas-fired plant in an era of declining sources of supply.

The Potomac Electric Power Co. (Pepco) is one of three utilities in the country doing a $9 billion, two-year study of ways to do this in different kinds of land. Some natural gas has been stored this way for years, occasionally in abandoned mineshafts, according to Pepco.

"As you put tunnel deeper and deeper, the pressure can get higher and higher," said Pepco project director Charles Smith. "The size of the cavern depends on the depth, the megawatt rating of the plant (the output) and the number of hours of storage you want, plus the sophistication level of the machinery." He said a typical cavern would be spread out finger-like in shafts connected like the tines of a fork. One might cover 250,000 cubic yards, about as much volume as a block the size of a football field and 47 yards high.

At the press conference, Samuel Behrends of Carolina Power & Light at Raleigh, N.C., said utilities want to reduce the number of power plants they have to build to meet future needs because inflating construction costs and rising interest rates mean everything they build costs more.

O. V. Holeman of Arkansas Power & Light said his firm raised peak hour prices to a level six times as high as nonpeak hours and installed special meters in an experiment to see what would happen. Usage declined 30 per cent among home owners during that time, he said, but admitted, "We got more revenue. The overall bills did not go down.

The utility spokesman talked of other conservation experiments and devices, including automatic shutoff switches that cut out water heaters or central air conditioners by remote control for 7 1/2 minutes twice an hour for customers who got a billing credit for agreeing to it.

One dissident was Craig Johnson, acting director of regulatory intervention programs for the new Department of Energy, who was part of the audience. "You're putting out a lot of misconceptions," he said.

"State public utility commissions would develop the rates under the pending law."

He added he was unimpressed by the utilities' listing of their innovations: "You guys are the leaders in this kind of thing. There are 160 utilities - after you go 10 deep on the list, what is the rest of the industry doing?" he asked.