THE huge postwar generation that nearly overwhelmed the country’s institutions of higher learning in the 1960’s has now begun to make its numbers felt in the growing scramble for new housing. As the children of the 1940’s and 1950’s begin to raise families of their own, they are leaving behind the singles’ apartments built just a few years ago to search the suburbs for single-family homes. Their numbers are so large-households headed by those between the ages of 25 and 34 increased by 3.3 million between 1970 and 1975-that the situation is reminiscent of the late 1940’s. At that time, returning veterans, plus young couples who had been unable to afford a place of their own during the Depression and then to find one during the wartime shortages, were clamoring for homes. Within a few years, the Levittowns and other suburban developments met most of the need, set new records for single-family homebuilding that still stand, and put in place the middle-class suburbia that shaped American life from the 1950’s to the 1970’s.