SUMMER IN Washington is the season of air-conditioning, and you would be justified in feeling some concern for the region's electricity supply. It's no worse than last summer, but demand is running very close to generating capacity, and a hot spell would mean more brown-outs. That wouldn't necessarily be the end of the world, but it would be a further reminder that the Washington area is doing only a barely adequate job of reconciling its steadily rising demand for power with its habit of resisting the construction of new generating plants.

There's no hope of importing more power from other areas, because the present transmission lines are already fully loaded and the public opposition to building more of them is even greater than to building generators. The immediate cause of the squeeze is that both of Baltimore Gas and Electric's nuclear reactors at Calvert Cliffs have been shut down for the past year because of a leaking weld discovered in one of them. There will be some relief in July, when the other goes back into operation. Over the next several years Pepco plans to install gas turbines at Chalk Point and Dickerson, Md. It's too expensive to use turbines to carry the base load around the clock and around the year, but they are very useful to meet the peak loads on hot summer afternoons. The District of Columbia, in response to neighborhood opposition, has refused to allow similar generators to be installed here in the city at Pepco's Benning Station.

But the new turbines won't create a sufficient margin of reserve capacity. Even if the weather this summer is no more than normally warm, the utilities expect peak demand to be nearly 3 percent higher than last year. The only way to balance the equation is through conservation, and both Pepco and BG&E are pushing conservation programs vigorously. Pepco has offered to pay $90 million over the next five years in bonuses and rebates to customers who conserve. That means, for example, a big commercial customer who installs more efficient lighting. It also means you, if you buy a more efficient air-conditioner.

If voluntary conservation doesn't suffice, the next recourse will have to be involuntary conservation. A brown-out is a 5 percent drop in voltage -- a slight dimming of the lights and barely noticeable except to delicate equipment like certain computers. If you use a computer, you might want to get into the habit of saving your work frequently as a defense against sudden attacks of amnesia when the temperature begins to rise.