ABIRD'S eye view of Washington offers vistas of rooftops all over town punctuated by funny little bubbles. Roofs of restaurants, department stores and houses both old and new are bubbling up with plexiglass lumps, pyramid, barrel shapes and all manner of windows to the sky.

"Years ago, when you sat down with a client to talk about his dream house," recalls architect Bruce Preston, cif you said 'window seats,' the wife would sigh a deep sigh and in would go a romantic window seat. Today, the magic word is 'skylight' -- everyone wants one."

Ads for in-town properties boast renovations complete with "sunny skylight in master bedroom." Promotional copy for a new luxury house recently placed on the market went so far as to call a skylighted bathroom a "botanical shower/bath" because of a builet-in planter.

Despite the fact that they are generally made of plastic, skylights are a manifestation of the anti-plastic, let's-get-in-touch-with-the-great-outdoors movement. Townhouses with sand-blasted raw brick interior walls characteristically display a mandatory collection of hanging plants and, of course, at least one skylight.

Skylights are a marvelous way of bringing light into a room. Houses built around the turn of the century often had skylights built into windowless second-floor bathrooms or illuminating staircases. One of America's greatest architects, Thomas Jefferson, liked skylights so much that he had 14 of them installed at Monticello.

It's easy enough to install a skylight today. Just cut a hole into the roof, making sure that you haven't weakened the stability of the roof joists or cut any electrical lines. Frame up the hole inside and out and set your "light" down over the space. To prevent leaks, some skylights come with their own "curbing" or flashing to create what one hopes will be a watertight seal.

The expense of this implosion of natural light is not that great -- prices for standard residential products (excluding installation) range from around $200 for a 4 feet x 4 feet single-glazed dome to $350 for a 4 feet x 6 feet double-glazed affair. Installation costs depend on the work involved but run around $300 to $400 for the sizes mentioned above.

In this frantic return to nature through the roof, most homeowners have considered only the aesthetic side of the equation, ignoring the potentially negative factors. Contrary to what would seem to be the case, most area skylights are not "parssive solar systems." While they may cut lighting costs, they tend to add to heating and cooling expenses.

"Most skylights in Washington are extremely inefficient in terms of energy gain and loss," says architect Vivian Loftness of the American Institute of Architects Research Corporation, one of the key researchers in a massive Department of Housing and Urban Development-backed study of passive solar design. "Because of the pitch of most Washington roofs," says Loftness, "skylights let in too much summer heat and allow too much winter hear to escape." She explains that the winter sun is low and that most rooflines are too shallow to allow skylights to serve as recipients of "direct gain" from solar heat. Instead, hot air flows upwards, finding the weakest point to escape -- usually the skylight. The angle of most area rooftops is perfect for collecting large amounts of summer sun, howeverm, trapping it (if the skylights cannot be manually opened) and forcing up cooling costs. "Ideally, a skylight here should be at a 45-50 degree pitch," says Loftness. She is quick to point out, however, that new gains and losses of energy have to be assessed on a case by case basis to take into account the location of the skylights and other windows, the insulation in the house, relationship to prevailing winds, and so on. A good point to remember, however, is that the average rooftop has about 3 1/2 inches of insulation, giving it an R-value (resistance to hear) of R-19, whereas a double dome (with one inch of air as insulation) has an R-3 rating. The larger the skylight in relationship to the roof area, the bigger the energy loss.

Architects recommend placing skylights opposite standard verticall windows to cut down on glare in a room. They also generally suggest that skylights face north to cut down on excessive summer hear gain. To avoid glare from a skylight, some architects suggest that the rooftop windows be set close to a side wall, so what the light generally falls on a wall, not in your eyes or in areas which might cause fading of furniture or wood finishes.

To overcome the problems of heat loss in winter and heat gain in summer, some sort of interior shutter or shade is recommended. In contrast to the advanced technology that led to the creation of plexiglass molded bubble forms, ideas for shading or shuttering skylights are crude. There are shades that are layered into sections with air traps between each section to form a kind of thermal guard; there are mechanized elaborate systems for built-in shades. One local architect built a kind of wooden louver system which can be adjusted by hoisting an 8-foot stick into a catch. Another solved the problems of harsh summer sun by covering each skylight in his office with a swatch of fabric. The most elaborate shutter system can be seen at the sirport terminal in Aspen, Colo., where 1,750 square feet of horizontal skylights are insulated with a system called "Skylids" by Zomeworks of New Mexico.

The system consists of a set of thick aluminum louvers filled with building insulation set inside the skylights. Each louver is powered by two interconnected refrigerant-charged canisters located on either side of the louber. Vaporization resulting from temperature changes causes the liquid in one canister to move from one side of the louver to the other; the weight shifts cause the louvers to open or close as the temperature warms or becames too cold. The whole system is both cumbersome and elaborate.

For most skylight owners, energy savings are sacrificed to aesthetics. Even on a gray rainy day, a skylighted room is bright and airy and may be worth the added cost.

There is one system on the market, also developed by Zomeworks, that seems to allow you to have your cake and eat it. It's called "Beadwalls." The skylight is essentially two surfaces of flat glass, set about two inches apart. A vacuum and blower motor charged with tiny white Styrofoam beads and controlled by a thermostat causes the space between the two panes to fill up with what appear to be unmeltable snowflakes (see picture) when it's too hot or too cold, giving the wall an R-value equal to a standard wall filled with 3 1/2 inches of insulation. This expensive piece of energy-conscious gimmickry appears to work well -- as long as the owner periodically feeds anti-static solution into the vacuum and blower motor to keep the beads from sticking to the inside of the glass.Washington's only "beadwall" has been installed by a high Carter administration official who prefers anonymity. The official concedes that "in order to support this kind of energy conservation, you have to be rich." The 7 feet x 13 1/2 feet system of three skylights (set at a 55-degree angle to capture as much winter heat gain as possible) cost around $4,000 to purchase and install.