And now, from the folks who brought you last winter's gas shortage, a new idea to lower gas bills: buy more gas appliances.

The Washington Gas Light Co., prohibited by the public service commission since March of 1972 from signing up new customers because of chronic supply shortages, has just completed the latest in a series of advertising campaigns to get existing customers to buy gas-fired air conditioning.

"Install whole-house gas air conditioning now," reads the flyer mailed or sent with monthly bills to about 20 per cent of Washington Gas Light's 536,000 area customers. "Dependable!. .. Famous gas company service is yours for the asking."

The reason behind this seemingly paradoxical campaign is that, like most gas companies in the region, Washington Gas Light has been losing customers and thus losing revenue. Charles Krautler, company public information manager, said 9,000 consumers have dropped off the rolls since 1972 through "normal attrition:" business closures, demolition of old urban housing, razing of buildings for parking lots and Metro construction.

The lost revenue - roughly $717,000 a year - can't be made up with new customers, and the old customers still have to cover standing capital expenses for pipelines and machinery. It translates into an additional charge for each remaining customer of $1.30 per year - "not much, but something," Krautler said.

The company, in other words, wants more business, but not too much more. "The supply situation is in a state of flux all the time," Krautler went on. "Before we take on new customers, we want to be certain we can serve the customers we still have . . . Air conditioning is a minor load and won't jeopardize the service to our old customers."

The most recent ad campaign lasted from late April to mid-June and resulted in at least 75 air conditioning unit sales, with more still trickling in, Krautler said. Although that is far from making up attrition losses, he said the company was "fairly happy" with the result.

Other companies in the region have also lost customers but have not resorted to appliance promotion campaigns to make up for it. The 14 gas companies that serve various parts of Virginia have all had showrooms displaying gas appliances, especially for use in summer when gas goes begging, according to James Dunstan of the Virginia State Corporation Commission, which regulates the firms.

"However, that was to a lesser degree than Washington Gas Light, which is very aggressive in its sales program," he said.

Dunstan added that declining customers levels are partially traceable to insecurity about future gas suppliers. "People are concerned after last win ter, so even though it's more expensive, most new homes are being electrically heated now."

Virginia firms have always been allowed to replace lost cusstomers with new ones, "but now many are losing more than they're signing up and the ones they do have are using less gas." Dustan went onn. "There's been a great increase in conservation . . . the companies aren't selling the gas they've got."

A spokesman for the Virginia Electric Power Co. (VEPCO) in Norfolk, which serves the Tidewater region, said its number of customers peaked in 1974 at 126,000 and now totals 121,697, with no new customers at all since 1974. "We haven't promoted appliances since 1973 . . . we're more concerned with getting a sufficient supply now so our emphasis is on conservation," he said.

However, Vepco's main revenue source is electricity, not gas, whcih, makes up only 4 per cent of the company's annual sales. "The weather has more of an influence on how much gas is used than the number of customers," the spokeswoman said.

Henry Leber of the Baltimore Gas Light Co. said his firm lost about 600 customers during 1976. He said the loss "isn't serious so far," and that the company had not done any appliance advertising for five or six years.

Washington Gas Light won permission two years ago to add coomercial cooking customers on a highly restricted basis and has put on 52, while another 100 or so residential customers disconnected during the 1968 riots have been reconnected Krautler said.

"We fully expect that at some point the supply situation will be such that we can begin taking on new customers," he said, "but we don't know when yet. Both suppliers (Columbia Gas Transmission Corp. and Transcontinental Gas Pipeline Co. of Houston) have indicated that suppliers this winter will be better will be better than last winter. We're just trying to use the excess capacity we have now . . . if you don't use it, you lose it."