IT has been reported that former President Jimmy Carter was denied access to a Boston restaurant because he was not wearing a jacket. The hostess, after close inspection of the Carter cardigan sweater, took her dress-code-policy position with a firmness that would have made Henry Kissinger seem like a Milquetoast. When a Secret Service agent pointed out that this was a former President of the United States being declared unfit for the society now nibbling cordon bleu delicacies within the restaurant, the hostess was quoted as saying, ''All the more reason he should wear a jacket.''
Our first response was to rush all three of our suits, plus a spare sports jacket, to the cleaners. Nothing in a long time has so signified to us that neo-populism is dead, and everybody better wear his neo-conservative costume if he wants to go on eating - at least at any place higher up the social scale than a fast-food drive-in.
We remember when a cardigan sweater was Mr. Carter's best ambassador. Never mind restaurants. It got him into the hearts of his fellow-Americans, as presidents like to say. Speaking from the White House on national television, Mr. Carter's cardigan sweater silently announced: ''I do not belong to a machine politician, or even a politician in the usual sense. I belong to a peanut farmer from Georgia. I am the uniform of a man of the people. If Abraham Lincoln were alive and turning down the White House thermostat to conserve energy, he would be wearing a cardigan sweater, too.''
How should a president dress? We can rest assured that any restaurant Mr. Carter couldn't get into might have to reject Lincoln and Andrew Jackson as well. But on the whole, the Pascal theory of clothes has ruled the White House. Pascal argued that if judges wore, let us say, green double-knit leisure suits instead of black robes and generals wore, let us say, filling-station overalls, both authority figures would lose a lot of authority.
Mr. Carter's cardigan sweater makes the oldest statement of American democracy - that a person does not have to wear a crown and a purple robe in order to govern a nation. The sweater bulkily clothes the hope that, in a democracy, an individual will be appreciated for what he is, not for his limousine or his house or, least of all, his tailor.
It is an ideal that has always trembled in the balance in everyday American life. In theory we Americans prefer our cowboys to our city slickers - when we put it that way. But then, why do we keep talking about ''power'' dressing? And why do we keep setting up these exclusive restaurants that won't let a country boy in a cardigan sweater through the door?
The double standards for presidents used to be resolved in a simple, if not very logical, way. When the president was on the job, he kept a very stiff collar in place when photographers were around. On vacation he was allowed to go casual, relaxing - preferably on the end of a fishing pole. Even so, a fellow had to be cautious. Harry Truman, who was more prone than most presidents to be human, once wore a wild tropical-print shirt on a Florida vacation, making all the front pages and prompting rude critics to ask, ''Can we trust this man to be President, even after he changes his shirt?''
Appoint those snobs maitre d'.
Dignity is the most difficult virtue to define in a democracy. Boston, of course, has been trying to define dignity all its life, in such concepts as the Proper Bostonian. In fact, maybe the Carter cardigan is a Boston problem. A few blocks away - attention: Rosalynn Carter - another Boston dining room stands guard against women in pantsuits.
We happen to like traditional dining rooms, but not when they're wall to wall with nothing but traditional dressers. A little variety in the diners, please, as well in the menu.
Nothing makes a worse case for rules and regulations than dress codes writ in stone. You're never going to keep out the riffraff that way, and we speak as a case in point. Why, we'd bet anything that Mr. Carter's cardigan cost him more than the Proper Bostonian sports jacket we can hardly wait to get back from the cleaners.