BACK WHEN I WAS in school, English teachers used to refer to something called the "willing suspension of critical faculties." What that meant, as far as I could tell, is that you were supposed to believe something that could not possibly be true. In the movies, this is called casting.

The picture that brings this to mind is a little gem called "My Brilliant Career," which is bound to become the cinematic darling of the women's movement. It is, after all, about a turn-of-the-century Australian woman who forsakes marriage to a very rich and very handsome man so she can pursue a writing career.

Where you have to suspend critical faculties is not in the plot but in the casting. All during the movie you are told over and over again that the woman is what is called "plain." She says it and her mother says it and her grandmother says it and you get the impression that everyone for hundreds of miles around is saying it. And the way everyone says plain -- linking it to her dismal marriage prospects -- it's clear that they don't mean she is just short of beautiful. They mean something close to ugly. She is, in fact, very attractive.

She is lovely. She has a fine, wide, dimpled face. She has a nice figure and while in the movie she is personable as can be, it is not her personality that makes her attractive. It is the fact that she is, clearly, attractive. Plain she is not.

It's ridiculous to make claims for the movie, which it itself does not, but there is a message to the film nonetheless. It is that through dint of personality and character and brains and indomitability, even a plain woman can become not only a literary and social success, but a romantic one as well. Since the movie is based on a book and since the book was written by the woman involved, this is probably what happened in real life. On the screen, though, it does not happen this way. On the screen, an attractive woman becomes even more attractive. This is not quite the same thing.

Movies do this quite a bit. In an "Unmarried Woman," separation and then divorce are realistically portrayed -- up to a point. What is not realistic is the Unmarried Woman's magical source of income and her uncommon good looks, which immediately bring her none other than Alan Bates. He, I daresay, could take the edge off separation and maybe even divorce.

What these movies do is announce they are about something and then duck that something altogether. They present a dilemma that they then don't deal with, and most often they do this when the issue is what a woman looks like. The old question of whether beauty is, in fact, only skin deep and therefore of fleeting importance is never answered in these movies.

Instead, what you get is a cinematic version of the old ugly duckling tale. The problem with that one is that the duckling is really a swan. It avoids the question of what happens if the duckling is really an ugly duck. The movies do this by casting attractive women to play plain ones. This is usually accomplished by having the actress play half the movie with her hair up and the last half with her hair down. This is the modern version of that old routine where the woman takes off her glasses and the man exclaims, "Why, Miss Jones, you're beautiful!" It makes you wonder if the wrong person has been wearing the glasses.

A classic in this regard is that classic itself -- "The African Queen." No amount of protestation on the part of Katherine Hepburn that she is a dowdy spinster succeeds in convincing either us or Humphrey Bogart that she is not, underneath all those frowsy clothes, Katherine Hepburn. In a somewhat different vein, we get Sally Field playing Norma Rae for whom, I assure you, life would have been quite different had she looked like Sally Field. She might have wound up living with Burt Reynolds, instead of sweating it out in some Southern textile mill.

What this sort of casting does is manage to gloss over the real importance of looks in American society. The consequences of looking plain are not dealt with when the actress playing the role of the plain person is herself stunning. If there is a message here it is that to be attractive, one has to be attractive to begin with.

In life, this is not the case. In life, there is real plainness, but there also is remedy aplenty. There is charm and personality and character and even, by God, intellect. H. L. Mencken once suggested that the kind thing to do was to "wink at a homely girl." That's nice, but it might be better to cast her in a movie.