Faced with $25,000 monthly electric bills, apartment manager Thomas E. Humphrey installed an IBM Series I computer that has turned the 481-unit Buchanan House in Crystal City into a kind of giant energy-saving space-ship.

Untouched by human hands, the air conditioning in each bedroom quietly shuts off for 3 out of every 15 minutes, and thermostats in 1,183 rooms automatically cycle on and off according to various schedules.

A weather station atop the building feeds temperature and humidity data to the computer. Ninety-two monitors check the angle of the sun as it makes its way across the sky, signaling the computer which rooms are in shadow and which in light so that continual adjustments may be made.

If the outside temperature hits a comfortable range, the big air conditioning chillers are throttled back to idle as 57 dampers click open all over the building and the outside air is blown in.

Humphrey figures the computer system, which cost $110,000 to buy and install, will save $50,000 a year on his electric bill. IBM told him he could reasonably expect to save at least $42,000 a year.

In big ways and little ways throughout the Washington area, people are intensifying their efforts to conserve energy and hold soaring energy costs in check.

Some homeowners have put in minicomputers that work the way Buchanan House's does. Many have installed wood stoves. An Alexandria motel is experimenting with a system that shuts off the lights and air conditioning automatically when a customer leaves his room.

A survey by the Potomac Electric Power Co., which sells electricity in Maryland and the District of Columbia, found that 55 percent of home-owners have caulked and weatherstripped their houses, 47 percent have lowered the temperature setting on their water heaters, and 48 percent said they are deliberately using their appliances less.

But it is across the river in Virginia, where the Virginia Electric and Power Co. has raised the price of electricity 47 percent in two years, that the ethic of energy conservation has become a fervent way of life practically everywhere.

After all, everyone uses electricity. And Vepco's increases have been on top of an 18 percent increase in the price of natural gas in the Washington area during the last year, and nearly a 100 percent increase in the price of home heating oil during the same period.

By contrast, Pepco's electricity rates have increased only 16 percent in three years -- the result of such factors as the absence of nuclear power plants and strong regulation by public officials.

Pepco charges twice as much and Vepco nearly four times as much today for electricity as they did just before the 1973-1974 Arab oil embargo -- and this the key to the conservation that is intensifying today.

Energy-saving computers are not just for big buildings. Donald and Lucille Crump have an "Energy Cruncher" computer in their six-bedroom house in Burke that shuts off the water heaterd for 3 minutes out of 10 and controls other appliances as well.

"It's fine if you can stand the furnace not running 4 out of 10 hours," quipped Lucille Crump. She said she thinks the system is saving money but, "as fast as Vepco goes up, it's hard to tell."

More traditional methods, work, too. Thomas and Mary Elizabeth Cox put a wood stove in their Burke house and slashed their electric heat bills from well over $100 a month to practically nothing.

Thomas Cox gathers his firewood for free.

"To me it's very appealing to heat your house without using Vepco or WGL -- in other words to be self-sufficient," Mary Cox said.

Both Pepco and Vepco report that their residential customers are using less electricity on an individual basis than they were just before the embargo touched off the nation's energy crisis more than half a decade ago.

Vepco's typical all-electric customer used 24,000 kilowatt hours of electricity in 1972 but only 19,600 in 1978. Nonheating customers used 8,600 kilowatt hours in 1972 but only 8,000 in 1978. n

Since 1978, those declines have continued, and the increasing prices show why.

That typical all-electric customer paid Vepco $439 in 1972. By 1978 he was using 18 percent less electricity, but the price tag was $901. Today it would be $1,365.

For the nonheating customer, those price jumps would have been from $157 to $380 to $557 a year.

For commercial customers, individual use has climbed slightly -- but the rate of that increase has slowed dramatically from 11 percent annually in 1973 to less than 3 percent today. With the recession, Vepco expects the slowdown to intensify.

These trends -- and the local picture here is mirrored nationally -- have deeply affected the financial planning of the electric power industry. Sales that spurted 7 to 10 percent annually in the early '70s now grow at only 2 percent or so each year.

As a result, companies are curtailing their expensive power plant construction programs. Vepco has just delayed construction of a huge new power storage facility in Bath County for several years, and Pepco last Thursday canceled construction of a $930 million power plant in Montgomery County, saying it isn't needed because people are conserving.

That brings to nearly $2 billion the amount Pepco has shaved from its construction plans since 1975. But the utility still has a 28-percent excess generating capacity over its peak demand -- a substantial safety factor.

Vepco, whose 17-20 percent excess capacity is closer to the industry average, has had such bad luck with maintenance of its nuclear plants and some older plants that it frequently must buy electricity from other companies at enormous cost to its customers.

Recently, for example, Vepco appealed to customers to turn off their air conditioning and imposed a 5 percent power cut to customers because the company unexpectedly lost 3,000 megawatts of its 9,000-megawatt generating capacity after accidents caused the shutdown of power plants, including a big nuclear plant.

Since plants representing another 2,000 megawatts of capacity were already out of service for scheduled maintenance, Vepco had to scramble to buy premium-priced electricity elsewhere while making the appeal to its customers.

Electricity that Vepco is forced to buy from other companies always costs a lot because those companies use their most efficient generators to produce electricity for their own customers, and their least efficient and often oil-fired generators to produce electricity for sale to Vepco.

While footing these bills, Vepco's customers at the same time must pay the huge depreciation costs of the Vepco plants that are not operating.

All of this adds up to increasing tension in the years ahead between the electric utilities and their customers.

"It's very hard for people to realize that the days of energy availability and lower prices are gone forever," said Irene M. Moszer, Vepco's director of forecasting and economic analysis. "The adjustment process that people will have to go through is going to be painful and there is only so much that most businesses or individuals can do."

Michael Van Atta, a Fairfax County energy consultant who sells energy-saving computers and other devices, puts it another way: "Vepco is like an animal hiding out there in the dark," he said. Nobody knows what it is [or] whether to believe it or not."

That seems close to the popular view of Vepco.

"I think it's ridiculous. Something just doesn't seem kosher," said Paul E. Reese of his Vepco bills. Reese has a small shoe store on Columbia Pike called Paul's Shoe Box, where he is constantly turning off the air conditioning and lights whenever possible to save money.

Said Reese: "I don't really believe that a lot of these increases are warranted. I would be the first to say there probably are people that do waste electricity and energy, but in this store here, a tiny store like this, for me to pay an average of $100 a month is ridiculous."

At the Old Town Ramada Inn in Alexandria, manager Jaap Vandervorm has put polar film on the windows and rigged some rooms -- on an experimental basis -- with a special lock system that automatically shuts off the lights, television and air conditioning when a customer leaves his room.

There can be problems with that if there are two people in the room and one goes for a drink at the bar while the other stays in the room. The locking system can get out of phase.

A more sophiscated system will be tried in a Western motel under construction in Springfield -- sound sensors in the rooms will pick up "spikes" of sound but not the hum of an airplane or a nearby car. This will signal a computer that the room occupant has returned so the computer can turn on the electricity in the room.

Vandervorm said the solar film seems to work fine in the summer but is little help in the winter, when the Inn's all-electric heat brings the biggest bills of all.

At the nearby Olde Colony Motor Lodge, manager Bill Williams has made some less modernistic but still effective changes to combat his $6,000 monthly electric bills.

The room maids are under orders to turn off electric lights and appliances in all rooms before beginning to clean. Lock boxes have been placed over the controls of air conditioners in public areas. A night watchman goes around systematically turning off lights. Williams shuts off whole wings of the motel during slack periods.

Williams isn't sure exactly how much he has saved, but he can remember when those $6,000 bills were only $3,500, and he is sure they would be a lot higher now if he had not taken strong action.

One reason people are turning to computers and other sophiscated energy-saving devices, according to utility company analysts, is that in many cases the easy savings achieved by insulation, weatherstripping and other traditional methods have been exhausted -- yet prices continue to soar.

Ron Rosh of Dale City was so upset by paying Vepco $111 for 3,380 kilowatt hours a year ago January that he set out to tighten up his house.

By last January, he had managed to slash more than 1,000 KWH's from his consumption, reducing it to 2,166.

His bill for that: $112.

"It all comes down to I'm being ripped off," he groaned. CAPTION: Picture, Manager Thomas Humphrey, above, of 481-unit Buchanan House apartments in Crystal City, estimated $110,000 computer saves $50,000 on his electric bill yearly. By John McDonnell -- The Washington Post