Housing for retired and semi-retired persons may be the hottest item in the residential marketplace in the 1980s.

The number of persons entering this age category is increasing rapidly and many of them are seeking a new way of living.

In the 1930s, '40s and '50s when middle-class couples reached retirement age, they tended to stay in the same homes. Usually, such couples had achieved the goal of paying off the mortgage and actually owning the home. These couples gave scant consideration to the idea of moving, even though their houses usually were as old or older than the occupants and were too large to serve their needs.

But that was another era.

Today's retirees are often more affluent, considerably more mobile and certainly more desirous of a change -- particularly if they have lived in a suburban neighborhood in transition or in the city.

They may want to stay in suburbia or in the city but they want something different -- usually a smaller, less expensive place with more security and less demand for upkeep and housekeeping. Additionally, they often want more recreation opportunities, whether tennis, walking paths, golf or swimming.

"Retirees need just about everything in their homes that other segments of the population require. The difference is that the retired need is (for those things) to be closer," according to one of the conclusions drawn from a forum held last year on middle-income retirees by the Federal National Mortgage Association.

Consider location. Homes for retirees should not be isolated. They should be fairly near stores, banks, hospitals, doctors, dentists, theaters, libraries and churches.

They need not necessarily be within walking distance of the facilities mentioned above but should not be more than a 10-minute auto ride -- and preferably not through congested traffic. Public transportation becomes more important, too. You cannot always count on being able to drive a car as years in retirement pile up. So check out the bus schedules.

The high-rise apartment has an allure for persons in retirement but not always for the person who has not previously lived in an apartment building with an elevator. However, one Washington area couple recently sold a large single house and moved into a first-floor garden apartment -- with an elevator -- and find it highly livable even though it's less than half the size of this couple's previous house.

This couple now has privacy and a good sound barrier -- highly important in multifamily living -- and is close to lots of recreation activities in an adult community. Also, they are closer to other people and have made new friends within three months. That's a plus for moving into a new environment: You make new friends easier and can always retain old friends just by working at doing it.

If there is any conventional wisdom about retirement housing and how to choose it, it's simply this: Start thinking about it long before you intend to make a decision. Read about new housing being created in your area for retirees and take notice of what people slightly older than you are doing about meeting this residential challenge.Many of them seek one-floor living to avoid the use of up-and-down steps in their senior years.