Several weeks ago, with appropriate fanfare, the Democratic National Committee unveiled six slick television commercials branding the Republicans as the party of "unfairness."

Everybody's favorite ad shows an elephant lumbering through a china shop, smashing crystal and crockery. A closeup has the elephant's hoof crushing a plate labeled "Social Security."

Turnabout is fair play, of course. The Democrats were presumably responding to a Republican commercial, equally slick and simplistic, in which a friendly postman assures you that President Reagan has kept his promise: Social Security checks are still keeping up with the cost of living.

It is jolly good fun. It is also terribly familiar, too familiar in fact. After the laughs, you suddenly realize that the Democrats and Republicans are going after one another -- electronically at least -- as if we had jumped straight from the 1930s to the 1980s with no events of consequence between. The Democrats are still running against Herbert Hoover and the Great Depression; the Republicans are still running against Franklin D. Roosevelt, the first of the federal big spenders.

That isn't amusing. Like the current slump, it's depressing. Goodness knows what our great political parties would do for slogans if somebody suddenly fenced off the ancient well of Depression-era issues. But the president did well with nostalgia in 1980, evoking a golden age that exists, mostly in his imagination. The Democrats can hardly be blamed for following suit.

But what has all this to do -- really -- with solving the looming industrial and employment problems of the 1980s?

The Democratic commercials imply that if Democrats regained full control of Congress, they would bring back our lost prosperity. No doubt the Democrats would have different answers. Would they be better? At last notice, congressional Democrats were offering public employment as the interim solution--a variation on the "leaf-raking" formulas inherited from WPA days.

A government job is undoubtedly better than no job at all. But government jobs cost a lot of money to create, and a lot of that money goes to arrangers skilled at the art of grantsmanship. They're poor substitutes for the jobs that a booming private economy generates. The failure of Reaganomics lies not in its aims but in its methods.

And what about the threat to Social Security? It is real enough. But insofar as it is the result of any partisan conspiracy, it's the result of a bipartisan conspiracy to entrench costly entitlements in law. The attempt to make Social Security a party issue, for short-term gain, will only make the system harder to put back into actuarial repair.

As this season's jolly television commercials (and others not so jolly) suggest, congressional elections are a grossly ineffective way to register the voters' will on national issues. Congressional elections tend to turn on local or parochial issues. To the extent that broad-brush commercials add national issues to that mix, they imply the possibility of a party discipline and coherence that vanished from Congress with the late Sam Rayburn and the seniority rules.

Come Nov. 2, we'll have our last laugh at the cumbersome elephant, or sigh our relief at the news from Ronald Reagan's avuncular postman, or conclude from a brutal commercial briefly tested by Jerry Brown in California that unless you're for a nuclear freeze you're for blowing up the world. Thus instructed, we'll pull the levers and a new Congress will be born.

My own hunch is that, for reasons having little to do with all this infantile advertising, the Democrats will gain heavily -- up to 35 House seats, perhaps, and maybe control of the Senate too.

The danger is that the parties actually believe the evasive myths contrived by their "media consultants." If so, the new Congress will probably be no more effective than the last at fixing what needs to be fixed.

We have turned our elections into electronic fun and games, assuring their triviality and irrelevance. Political fun and games, equally irrelevant, are the likely result.

As they say in the computer trade: garbage in, garbage out.