Maybe, just maybe, the fabled "personal digital assistant" -- the tiny computer that goes everywhere with you and keeps you in touch -- has already arrived in force. It is right under our noses. Or rather, on our belts or in our purses.

The pager. It doesn't have a fancy name, and it doesn't get much respect. It's so common -- there are about 22 million out there -- that we take it for granted. Yet the thing keeps multiplying and learning new tricks, doing jobs a lot more complicated than simply telling us that someone wants to talk.

Now the Federal Communications Commission has auctioned off licenses for the next big step, "two-way paging." These devices would do what existing ones already do: receive phone numbers, stock quotes and messages. They would tell us the time and remind us of appointments. But they would give as well as get -- sending messages out over the air.

Sounds a bit like a stripped-to-the-bones Apple Newton, doesn't it?

How different things are than in 1949, when commercial paging got its start. The first units received voices. When people called the service company to have someone paged, operators broadcast their names to all paging units in the area. CB-radio style, you listened for the messages for you and ignored the rest.

Years later came the beeper. The paging company could target its signals. It could send out a signal that would set your beeper, and yours alone, to beeping. That sound generally meant: Call the office, or call our operators and we'll give you the number of someone who's trying to reach you.

Later the units went digital, acquiring small liquid crystal displays that would give the phone number of the caller. You dialed the number direct. Then, a decade ago, letters were added -- the things could now receive brief messages.

Paging entrepreneurs proliferated (there are about 2,000 services nationwide) and got ever more creative: Services that once worked only locally, searching for you in just a single city, went national.

USA Today news now goes out to pagers, as do stock quotes. Companies use them to broadcast internal messages to traveling sales forces, restaurants to inform waiting diners when a table is ready. Electronic mail services use them to deliver messages to people on the run.

And drug dealers use them to deal.

Begun as a business tool, paging is increasingly going personal. Parents page kids at the playground; babysitters page parents when the baby is sick; pregnant women page fathers when labor pains begin. It's not a big expense. Pagers can be rented for $15 a month. Economic and Management Consultants International Inc., a Washington research firm, found in a recent survey that more than half of all new pager customers get them mainly for personal use.

Still in use through all this change are a few voice-based pagers. But few companies offer them because they hog radio frequencies. Operators would much rather use their limited supply of frequencies to field many non-voice units than a few voice ones. That problem is being worked on, though -- scheduled for introduction in 1996 are frequency-efficient voice units that will transfer a voice-mail message to your pager for storage, replay etc.

All of these services are one-way. But that soon will change, with pagers that talk back. Motorola Inc., the country's main manufacturer of the pagers, is offering a model called Tango, a six-button device with a small screen. It can receive messages and store up to 100,000 characters of information. It will alert you to appointments and tell you the time.

But where it's really different is its ability answer the big question of today's paging: Did my message get through? A message to this pager can automatically trigger it to send out an acknowledgment, which is then conveyed back to the sender.

This outgoing channel can also conserve scarce space on the radio spectrum. Before sending a 2,000-word message, for instance, the paging system might first send out a query. Are you there, Unit No. 12345? If it got back a yes, it would go ahead and send the full text.

Or the unit might periodically emit a signal that says to the local service, Pager No. 12345 is now in this city. The next time a national paging message seeks out that unit, it could go direct to the right city.

But what about Tango sending out substantive messages? It is too small to have a keyboard. So it would come preprogrammed with boilerplate messages that you could select, along the lines of "I got your message and will comply" or "I can't do it and will call you."

Motorola sees customized messages stored in your pager as well -- the paging service would program into your device 15 or 20 responses that you wrote yourself. You would select the appropriate one -- "Get out of my life," perhaps, or "Great idea!"

Detailed replies composed on the spot would be possible too, providing you had a laptop with you. You would type your reply on a laptop, which you would then connect to the pager.

So, show some more respect to the pager. Think of it as a tiny computer. The Personal Communications Industry Association, the pager industry's trade group, estimates that there will be 35 million of them around by 1998. Who knows -- one of the converts might be you.

An e-mail correspondent points out that in my last column I gave some bad information about what happens when air traffic control computers fail. The standard backup in those situations is -- other computers.

John Burgess's e-mail address is burgessj@washpost.com.