The first letter I opened yesterday hit me right between the eyes. Shirley Krutilla of McLean wrote:

"I'd like to ask you a question about your position on buying American rather than foreign cars. If, in the past 10 years, all Americans had followed your advice and bought only American cars, what would have been the motivation for American automobile manufacturers to build smaller, gas-efficient models?"

Touche, Shirley.

I have some answers, but they are not good enough to detract from the validity of the point you make.

Answer No. 1: I didn't advise people not to buy foreign cars. I just said I couldn't bring myself to buy one when I saw American jobs evaporating.

Answer No. 2: I am a member of so many minorities that it never occurs to me that any great number of people will be acting, reacting or thinking as I do. I just hoped I could persuade a few people to join me in bucking a trend that threatened our basic industry.

Answer No. 3: It's terribly unfair of you to inject logic into an emotional issue.

Seriously, Shirley, I don't think American auto makers need to be taught any further lessons about the popularity of high-mileage cars. What they need to be taught now is how to make them efficiently enough to win back their customers.

This may take longer than some people think because so much "lead time" elapses between the development of a new automotive idea and the production of the finished product.

Example: A reader suggested that autos could use a system of red, yellow and green lights to let other drivers know when the fellow ahead has his foot on the accelerator, when he is neither accelerating nor braking. I phoned Detroit and talked to some design executives.They told me they had long been interested in such a system. However, they would need a few more months for testing. And then it would probably be three more years from the drawing board to the production line.

That was 15 years ago.No such signal system has come off a production line yet, but if you were to ask Detroit about it today you'd probably get the same answer I got 15 years ago.

I hope the big brains up there have finally gotten the message that they can no longer stand pat and survive. PERSONAL NOTE

Ann Buchwald: Letters are pouring in to tell me that if I wasn't such a dummy I would have understood your directions for hanging up a pair of trousers. If everybody who has written to scold me buys a copy of the book you'll be rich enough to hire John Riggins and donate him to the Redskins. THE ORATORS

In yesterday's Washington Post, staff writer Robert G. Kaiser gave us an interesting analysis of media coverage of the presidential race.

He quoted Johnny Carson's comment about the debate being sponsored by the League of Women Voters:

"They say that if Carter doesn't show up for that debate, they're going to put on an empty chair while Reagan and Anderson debate. You know what bothers me? Suppose the chair wins?"

We laugh ruefully at this bit of topical humor for the usual reason: there's so much truth to it. This is a year in which all the candidates are disliked by many voters and all the candidates seem determined to find a way to lose. The most frequently repeated joke is that "None Of The Above" is leading in the polls.

Ronald Reagan has been criticized for flubs like his China policy and calling the Vietnam war "noble." He deserved most of the criticism, but I am sorry he was clobbered for saying, truthfully, that we didn't go to war for selfish reasons. We wanted to help South Vietnam defend itself against attack by communist invaders.

But Reagan didn't choose his words well, and they came flying back at him in a fierce barrage. His China statements were a fundamental blunder. And he didn't endear himself to many voters when he was the first to respond to new Iranian demands and said we ought to give Iran everything it asked. A thinking person would not have cut the legs out from under his president and weakened his country's bargaining position.

A wise man once said, "It is better remain silent and be thought a fool than to speak out and remove all doubt." I haven't been able to find this line in a reference book, so I can't quote the words accurately, but I'm sure you'll recognize the sagacity inherent in the music.

If you know who wrote the line, please tell me. Meanwhile, somebody should tell the candidates that at the rate they're going, the empty chair may indeed win.

Politicians ought to rest their vocal cords occasionally and give their brains a chance to catch up with their mouths.