Have they lost a friend!

''Have we lost a friend?'' the postcard from the car dealer asked. The address side was wreathed in flowers, pink and yellow roses cradling the signature. The scripted question was in someone's best calligraphic hand. A cartoon face looked out at me, sad and questioning. Had they lost a friend? You bet they had. Two months earlier I had sued them.

No matter. The inquiry obviously had been sent by an oblivious salesman who was wondering if I knew about the new fall line. I, in turn, wondered if he knew the irony of his own.

Of all the affectations that mark our theatrical society, where people are always ''on,'' calling each other ''dahling,'' ''sweetie,'' ''honey,'' and ''dear,'' none so offends as the taking of the name of friend in vain.

A few days later I was to see just how pervasive such bids for friendship were to become. The occasion was a political rally, and while I knew that candidates were fond of calling strangers in their constituency friends, I was unprepared for the degree of endearment that issued from the local leader. It was ''dear friends,'' ''my very dearest friends'' (all 500 of us), and ''friends of my heart.''

Of course, I realize that the car dealer and the politician are not my only friends. For years, I've been told I've had a friend at a certain bank, and only last week I received a number of letters from friends at magazines urging me to take out subscriptions. The proof of their being good friends was their special discount to join.

It may be necessary at times to be a friend of the court (amicus curiae) even under the most litigious of circumstances. But to be suddenly commissioned as a friend by total strangers is quite beyond belief - and acceptance.

Where Damon might do for Pythias, Horatio for Hamlet, or Butch Cassidy for the Sundance Kid, I draw the line at instant affection.

In such cases, ''nimia familiaritas parit contemptum,'' or, as Cervantes wrote in ''Don Quixote,'' ''I find my familiarity with thee has bred contempt.'' But whereas familiarity among true friends also breeds affection, familiarity between strangers pretending to be friends does not. Those who so presume to call us ''friends,'' are trespassing on intimate territory.

If blood is thicker than water, then the stream of consciousness that feeds friendship is thicker still, filled as it is with the rich ore of years of trust , shared experiences, the debris of emotional turmoil, jettisoned without guilt or sense of reprisal.

Friendship is the one relationship we have that is built of choice and sustained by deliberate renewal. To have a friend means to be a friend.

To be a friend means the opposite of possession; it means to have the capacity to look within and deliberately, compassionately, constantly, give what is important, anticipate what is needed, cherish what is received.

The car salesman asked the wrong question. One never loses a friend.