They are the closest things the real world has to the Dick Tracy wrist radio of comic strip fame: paging devices that double as wristwatches. Now starting to roll off production lines, they have been tested in the Washington area and could be on the market early in 1991.

Weighing about two ounces, the watches are heftier than ordinary timepieces -- more like a diver's watch or a watch with a calculator.

In addition to giving the time, the watches can display and store telephone numbers after receiving them by radio, but they cannot send anything out.

More than 8 million conventional pagers, most of them riding on belts, are in use in the United States today. They are primarily professional tools, often used by doctors or service workers. Paging companies hope that watch pagers will provide convenience and cachet that will help create millions of new customers, including ordinary Americans using them to stay in touch with family and friends.

Some in the industry see the pager taking many novel forms in coming years. "Could the pager be a lapel pin, or a necklace?" asked Stephen Burdette, managing director of Bell Atlantic Paging. The watches, he said, are "the first of a long line of what we think are going to be much, much smaller paging products."

But questions of cost -- the first watches will retail in the $200 to $300 range -- and whether ordinary Americans really want to be reachable at all times make it hard to predict how well the watches will sell.

Like most things electronic, pagers have grown in sophistication and shrunk in size dramatically since their introduction more than 40 years ago. Early models were clunky and simply beeped to tell the user to call a central phone number, where an operator conveyed a message.

Today's pagers are smaller and typically can receive a phone number or a brief written message, which is displayed on a tiny screen. They can store numbers and be set to vibrate rather than beep in places -- a movie theater, for instance -- where sound would be unwelcome.

A key sticking point to market growth is the fact that most pagers hang from belts and are not easily concealed. Pager makers have tried to address this by changing the shape and the place where the device is carried. Motorola, for instance, came up with a pager that looks like a fountain pen and is meant to appeal to executives.

Wristwatches are even more discrete. The companies hope that people will strap them on routinely each morning, just as they now do with ordinary watches. Watch pagers also are expected to be targeted at women, whose clothing styles don't encourage belt units and who haven't enthusiastically bought pocketbook units.

The technical challenge has been to make the pagers small enough to fit in a watch but reliable enough and with enough range and battery life to be practical. Modern microelectronics has made it possible to compress them to a size that paging companies are gambling users will accept. Antennae are in the watchbands.

"Most of the big firms are going to be marketing these pagers in the next year," said Andrew Roscoe, president of Economic and Management Consultants International, a consulting firm dealing with the paging and car phone industry. Later generations of wrist pagers are expected to be smaller and less distinguishable from ordinary watches.

Motorola Inc. and Timex Corp. jointly developed a watch that about 30 people tested in the Washington area this spring in conjunction with Metromedia Paging Services. The company says the watch runs for as many as 40 days without a change of battery and will be available for less than $300, but at present there is no firm marketing schedule. It is compatible with many existing paging systems.

A San Francisco-based start-up company called American Telephone & Electronics Corp. (AT&E), meanwhile, has teamed up with Seiko of Japan to make what is for now the only rival model. To retail at about $225, the watch claims a battery life of as much as a year and is being tested in three cities. But it uses a different technology that will require AT&E to build an entirely new system city by city. The company says Washington can expect this service early in 1991.

But will a true Dick Tracy wrist radio, one that will allow people to talk to others, ever arrive? Many specialists in the industry believe it will be technically feasible sometime in this decade. But the question is, would enough people want it to create a mass market?

Tom Stroup, president of Telocator, a trade association for the paging and mobile phone industry, noted that wrist radio conversations wouldn't be private. Tiny new cellular phones, small enough to fit into a shirt pocket, may be the way this type of communication finally comes to pass, he said.