Pure democracy may cease to be the Holy Grail of the Romantic Left and become an awkward reality.

Since December 1977, Warner Communications has been experimenting in Columbus, Ohio, with QUBE, a system of two-way cable TV. Each of the 30,000 participating homes has a console that allows the viewer to respond to the station. For example, when the announcer says, "If you like the show, push yes," the viewer dutifully pushes, a central computer at the station tallies the results and flashes them on the screen: an instant rating.

QUBE's executives expect the system will spread to the entire country. Next year, Houston and Cincinnati will have QUBE.

The system has been used for things like selling books. A salesman reveals a work's astonishing meris, the excited viewer pushes a button to indicate his desire for a copy and the computer automatically retrieves his name and address from memory. Two days later, he gets the book and a bill in the mail.

QUBE also permits the audience to take part in games.

Warner does not permit abuse of QUBE. In the hands of a less scrupulous company, two-way television has enormous potential for invasion of privacy. People would push buttons to answer a variety of questions. In time, the computer could automatically accumulate an elaborate profile on subscribers: political preferences, choice of books, eating habits, who was at home when.

Such a data base, combined with information from other sources, would tell a manufacturer that buyers of Seventh Heaven Organic Kitty Litter average $27,000 a year, have a master's degree and 1.3 divorces, and live in condominiums. This comes close to being watched by television and wraps the public much deeper in the growing web of electronic surveillance.

Another danger is the instituting of plebiscitary democracy. Two-way television would soon cater to the national mania for political polls. Few newsmen could resist the temptation to conduct a nightly poll on the issues of the day. Nor could the audience resist the fun of seeing their opinions reflected on TV. Should two-way television set in nationwide, a national tally would probably follow. Stations would have little difficulty putting their totals on a telephone wire to a computer in New York. QUBE has already polled its subscribers on a presidential speech and had the answer televised nationally.

One imagines Walter Cronkite asking, "How many think the B1 should be built?" Millions of fingers descend. Within seconds the answer appears on the screen -- and perhaps at the station, broken down by congressional district or even by name and address. Few congressmen would dare disregard so clear a mandate. These direct, if unofficial, votes would have tremendous influence over the legislature.

In a small community faced by simple problems, pure of even plebiscitary democracy might work. But American society is massive, incomprehensively complex and beset by problems that can scarcely be counted, much less understood. Specialization makes many matters comprehensible only to specialists. An intelligent and well-informed person may be able to decide whether a stronger military is desirable; unless he is a graduate electronics engineer specializing in strategic aircraft and privy to secret information, he cannot know whether a specific aircraft is a good idea. He will, nonetheless, push a button to register an opinion.

And, of course, a high proportion of the public is not well-informed. In the last few days, I have seen polls indicating that 39 percent of the public never read books, that only 34 percent know who represents them in Congress. The cliche that television aims at an eighth-grade mentality is reasonably accurate. Beyond the beltway, interest in all but local questions drops off sharply.

To encourage the uninformed to vote on detailed policy is unwise because it is certain to produce Gong Show politics based on the enthusiasms of the moment. The public mood fluctuates wildly, but stability is essential to policy. For example, the energy shortage tends to be forgotten when the gas pumps start and to be resurrected when they stop. Long-term policy isn't possible in a Gallup government.

The virtue of democracy is not that it promotes the rule of the people, but that it prevents the abuse of the people. The best argument for abolition of literacy tests was that the power to vote lessened the abuse of a class of people. It was not expected that the illiterate votes would improve the quality of policy.

A delicate balance exists between giving the governed too little power, which leads to tyranny, and giving them too much, which leads to government by whim. The point of representative democracy, as distinct from pure democracy, is that it makes the legislator responsible to the people without making the people responsible for policy. Technology is rapidly outflanking representation.