If you want to get a loan at a bank, you'll need to remember your Social Security number. If you get stopped by a policeman, you'll need your driver's license. If you shop at a department store, your credit card may be useful. Why then are we so frightened of a national identity card?

The question arises in respect to Jimmy Carter's plan for halting illegal immigration. Immigration officials tell me privately that the Carter plan can't possibly work. Why? Because it penalizes employers for hiring illegals without providing any means by which an employer can identify an illegal.

The illegal may have - probably does have - a forged Social Security card and a forged birth certificate for which he may well have paid most of his life savings. Is the employer supposed to spot the forgery?

What is likely to happen under the President's plan is that employers will refuse to hire anyone who looks "different", thus making life difficult for legal immigrants and all U.S. citizens of Spanish. Portuguese or Latin American ancestry.

Yet, the American Civil Liberties Union and the AFL-CIO are adamant in their oppositions to a national identity car. Both organizations fear the establishment of what might become a kind of national work permit that the government could, for reason of crime or political dissent, see fit to withdraw.

We have, both these organizations argue, gone through periods in this country of witch-hunting and political hysteria, and despite our good intentions there is nothing to prove that we won't go through such periods again.

There is logic to this view. In the 1950s, for example, might we not have been strongly tempted to withdraw the identity cards of all persons listed all the Attorney General as subversive?

And we have also gone through periods of violent dissent. During the period of student unrest in the 1960s, might we not have sorely tempted to withdraw the identity cards of all student protestors who destroyed property?

The problem troubles even those who are most concerned about the fact that "the flood of illegal aliens," in President Carter's words, "is severe and getting worse."

Rep. B. F. Sisk (D-Calif.) has introduced a bill that attempts to get around it, at least temporarily. He would call on the government to print a tamper-proof Social Security card and provide that it need be presented only by those who apply for a new job. The bill has some moderate and liberal support.

But Sisk realizes that over a period of a generation or two, every American would have such a card, whereupon it might become exactly what its opponents fear.

European democracies have used national identity cards for years without turning them into instruments for the benefit of gestapos. Americans are afraid of ourselves.