IF YOU HEAT YOUR home with natural gas and add an electric heat pump, your gas consumption will go down. But if you live in Maryland, your gas bill may go up - because the Washington Gas Light Company's Maryland rates include a heat-pump surcharge that could amount to $30 per month. General Electric, a maker of heat pumps, thinks that the charge is meant ot keep the pumps out of this marketplace. The gas company maintains, though, that its real concern is the more general one of how to deal with customers who use alternatives part of the time.

That aspect of energy conservation is just coming into focus. To consumers, heat pumps and such are much like insulation and weather-stripping; their value is in saving money and energy. To utilities, though, there is a major difference. Insulation reduces a home's energy needs every day. The new technologies do not. Add-on heat pumps will warm (or cool) a house until the temperature drops below about 30 degrees Fahrenheit; then the old gas furnace goes on. Solar hot-water and space-heating systems need conventional back-ups for cloudy days.

Thus, as these devices catch on, a gas company can expect lower consumption and lower revenues in temperate seasons - but no less demand for services when the weather is foul. And thus WGL is worryi*ng about how to maintain its full system and cover its fixed costs with more and more erratic revenues.

It's real problem. Slapping fat surcharges on the new technology is not a fair or far-sighted solution, though. Those fees can inhibit competition and discourage useful conservation. Applied to existing gas-heat customers, the fees are downright punitive; when a homeowner with a gas furnace adds a heat pump, his peak-period, cold-day demands for gas do not necessarily increase.

It would be better for utilities to gain more steady revenues by covering more fixed costs through flat charges on all customers. WGL is already levying "system charges" that separate some of the cost of service from the costs of fuel. That way, customers who put their gas furnaces or water heaters on stand-by still pay something to keep that service available. Meanwhile, the cost of per therm of gas may be held down, which helps everyday consumers a bit. It's not a perfect remedy, or easy to work out, but none of the real issues of energy costs and choices is simple any more. Utilities and their customers ought to face up to that, instead of sniping at the new factors that complicate their lives.