Since World War II, Americans have made a fad out of compact living. First, the dining room was eliminated. Then the large, old-fashioned kitchen was reduced and squeezed into an efficient line-up of utilities behind folding doors. Finally, the basement was pulled out from under- wasted space, it was said, and it raised the cost of home building. But now the pendulum is swinging in the other direction. Three out of five houses built recently in the Middle Atlantic states have full basements. The same is true of Northeastern and the Midwest states. Evidence like this should make the sales-minded contractor think twice. After all, you still have to provide some space above ground for a heating system and utility room which involve addition cost. And before you lay the floor for a basementless house, you still have to dig pretty deep for trenches and to pour footings. If you just went ahead and scooped out the entire area of a house, you would have a basement for only a few hundred dollar's extra cost and lots of extra space for a growing family.