dwellings, circa 1998. The places we'll live in during the next decade, and beyond. THE HOUSE: SMART [ cf. THE HOME: FAMILIAR ]

WE'LL call them John and Joan Jennings. They are a two-income family, mid-level executive types with some yuppie preferences. And, since the apartment block is going condo anyway, they've opted to go all the way and invest in a single-family home of their own. Theirs will be a special house: They will be able to talk to it, and it will talk back. They will give it instructions, and it will obey. In short, it won't just house them; it will be their servant as well.

For several years now the National Association of Homebuilders at its research center here has been developing a ``Smart House'' - the wave of the future, as many see it. Construction on 20 prototype homes in the United States and Canada will start next summer. The 100 or so scheduled for 1990 will be the front end of more than 5,000 ``demonstration'' homes that will be completed in the early part of next decade, and as many as 8 million units 10 years from now, condominiums included. Retrofit kits that will turn your 1850s Cape or Garrison into a Smart House are expected by 1992.

So what can be expected from a ``thinking'' house? Let's look in on the Jennings household:

No one is home for much of the day, so the house, not sensing any movement, has let the interior temperature rise into the upper 80s to conserve energy. Normally the air conditioning will come on around 5 p.m. to bring the temperatures to a more acceptable 74 degrees F. by the time the couple returns home at 6. But on this occasion, business commitments will keep them both in town later than usual. So Joan phones home to tell it they'll be late.

The computerized answering service takes the instructions (inserted via the phone's push buttons) and tells the air conditioner to hold off for an hour. The stove, with dinner waiting to be cooked, is similarly delayed, as is the water heater.

When the couple finally return, the house is pleasantly cool, the water is warm enough for an after-work shower, and dinner is nearly ready.

The voice-mail center bids John good evening and announces the time in pleasant tones, then tells him that three telephone messages have come in, the doorbell rang once that day, and letters await them in the mailbox.

Later that evening the Jenningses take a break from watching television to ask the same TV monitor to give them a rundown on the day's energy use and notes a slight decrease in air-conditioning costs, presumably because it turned on an hour later than usual. The lawn sprinklers, it tells them, have not been used for the past 24 hours, because the soil is still moist enough following the thunderstorm two nights ago.

On going to bed, the Jenningses check a schematic on the TV monitor that jumps from room to room, showing that all doors and windows are closed and locked except for several windows on the second floor, which are deliberately left open to let in some of the cooler night air. The monitor will remind the couple to close them before leaving for work the next morning. The schematic of the kitchen shows that all electrical appliances are turned off and that the refrigerator door is not ajar.

All lights turn off automatically when the house senses no movement in a room for more than a minute, but will switch on again the moment someone walks in. At the same time the house knows enough not to turn on the light simply because the cat wakes up and trots over to the milk saucer. Yet it can be programmed to wake the dog if a prowler is detected outside. Inside, an intruder would trigger an alarm that no one could sleep through.

In the morning the coffeemaker is activated several minutes before the alarm radio turns on. The TV comes on and turns first to the weather channel before switching to a news program (Joan's preferred sequence).

In the early hours of the morning, the washing machine did the day's laundry, because the local electric utility rates are cheaper at that time. For the same reason the dishwasher waits until 3 a.m. If the garden calls for it, this is when the sprinklers come on, because water pressure is invariably higher at this time.

Now if all this sounds too remarkable to believe, consider this: The new Smart House requires no technological breakthrough. All the various sensing and other devices are already on the market in one form or another as individual items.

``All we are doing,'' says Ken Geremia, spokesman for the Smart House developers, ``is gathering them together into one package.''

To do this, however, one innovative development had to take place: A single unified cable (a composite of several wires encased in a ribbon of plastic) was developed that distributes electrical power, control/data signals, and audio/video/telephone signals to all corners of the house.

In other words, where homes presently have one wire system for the power, another for the telephone, a third for cable TV, plus low-power wiring for the doorbell, the Smart House will have just one. That means any appliance can be plugged into any outlet. You can plug the telephone into the same outlet you were just using for the hair dryer. You could move the portable TV to any outlet in the house and still receive a cable signal.

Special multi-use receptacles at the outlets and matching plugs on the appliances, appliances together with computer chips that identify the type of appliance being used, make this sort of convenience possible. It's also safer.

For instance, the moment you plug in the iron, the chip in the appliance tells the central power source what it is and what sort of power or signal it needs. Then the correct power is supplied. If the iron is accidentally knocked over, the chip indicates that something is amiss, and the power is automatically shut off. Similarly should a short occur in an appliance being used, it won't blow a fuse and plunge a third of the house into darkness. Instead, the power is shut off in a fraction of a second, only to the appliance involved. Everything else will continue operating.

Should a child decide to push the end of a paper clip into the outlet just to see what will happen, nothing will. Not having a built-in chip, the paper clip can't tell the central power source what it is or what it needs, so no current will be supplied.

The system also includes a low-voltage backup system that would provide essential devices with emergency power in the event of an outage.

How much all this convenience, energy efficiency, and security will add to the cost of a house depends on many variables. Putting in the simplified wiring system would be less costly than installing the spaghetti-like array that has to go into a new house at present. But the computerized power-distribution center will cost more than an ordinary fuse box.

The system's cost will also depend on how many sensing devices and TV monitors the occupants want. Not everyone will want to be told that there's mail in the box or that someone came to the door while you were out. Also, appliances being adapted for the Smart House are likely to start out more costly, but would no doubt come down in price.

For all these reasons, then, Mr. Geremia is reluctant to suggest how much more Smart House capability will add to the cost of a new home. Surveys show that would-be homeowners are prepared to pay between $5,000 and $12,000 extra for Smart House technology.