Architecture is the stuff that cities used to be defined by -- and may be again. Experts say that high energy costs are spurring a return to architectural regionalism. The result, they say, is that areas of the country will once again be identifiable by the design of their buildings.

"Universal formulas, which we used for so long, don't work anymore, and architects are realizing they have to adapt buildings to local characteristics," says Paul Kennon, president of CRS Inc., Houston architects.

This trend isn't new; prior to World War II, an Oregon house differed from a Cape Cod house, which differed from a Georgia house. The differences depended on the area's climate, lifestyle and availability of materials. But the era of cheap energy tended to minimize, if not erase, the importance of these differences.

On Cape Cod, for instance, houses historically had long roofs facing the north to protect against the north winds. Small windows kept in the heat. In contrast, homes along the humid Georgia coast had high ceilings that let warm air rise to the top. Windows were tall to ease air flow through the house. Porches gave shade.

But with the advent of air conditioning and cheap energy, "we found we could create artifical environments instead of developing architecture that dealt with the climate," says David Meeker, executive vice-president of the American Institute of Architects.

So in the South, he says, tall rooms disappeared because air conditioning took care of the heat. Windows and lumber became a standard size, in part the result of a housing boom that fostered mass-production techniques. "We began to have a blurring of the regional character," Meeker says.

Now that's starting to change. It's a slow process; architects say that it takes time to translate ideas into buildings, and that design decisions typically are guided by what worked before. But they say that the historical preservation movement and a renewed interest in the cultural heritage of a region already have brought some changes. Expensive energy promises even more.

"There was some increase in regional architecture before the energy crisis -- in San Francisco, for example," says Richard Langendorf, professor of architecture and planning at the University of Miami in Florida. "But the energy situation not only helps to increase interest in it, it also provides a much stronger economic rationale."

Americans first reponded defensively to the higher energy costs: they turned down thermostats, put in storm windows and bought lower-wattage light bulbs. But now, architects say, they're starting to go beyond that on new buildings.

Southeastern homes once again are being built with porches and tall windows. Southwestern buildings are using adobe and masonary instead of relying on air conditioning to cool light frame houses. In the Pacific Northwest, designers are putting broad overhangs on windows so they can be opened in rainy weather, permitting air to flow through the house.

The American Institute of Architects figures that there are at least 16 different climatic regions in the U.S. "That's at least 16 different ways to solve the problem," says Meeker. Among the regions: High Desert; Texas Coast with moderate winters and lots of rain; Pacific Northwest with few extremes in temperature but much gentle rain, and Northern Tier with cold winters and high winds.

Still, experts insist they can't just imitate past designs. New technology won't allow it. "It's tough to keep a Colonial house looking Colonial and adding solar design," says Walter Richardson, an architect in Newport Beach, Calif. "The solar panels, roofs that turn in all directions -- these aren't compatible with all the old styles."

Furthermore, construction materials have changed in both cost and availability. The upshot, says Kennon in Houston, is that "we're trying to blend old, traditional styles that were well adapted to the climate with new ideas."

He says that in San Antonio, for instance, homes are being built with arcades, overhangs that protect windows and interior courtyards. But new, lighter materials are often being used instead of usual thick, heavy stone.

The interiors of homes also are changing by region. Northeastern homes traditionally had kitchens and breakfast areas on the east side and living rooms on the west, according to Harrison Fraker, a Princeton, N.J., architect. In the South, he says, homes had parlors on the north side, with entry rooms and halls facing south and west.