In France, excellent directors must be growing on every pomegranate tree or lurking in every ash-can. This time it is Marcel Carne who has sent over a directorial masterpiece in "Port of Shadows." Casual movie-goers, who are frequently puzzled as to what a director does besides sit in a canvas chair, could well study this picture and see how direction can make a film great.

They would discover Carne's success in creating mood or atmosphere--here one of acute depression, of utter hopelessness--by a combination of action, settings, lines, incidental characters, facial expressions, and omnipresent fog. They would feel themselves drawn into this gray morass until they themselves know the inevitable bleak prospect awaiting these characters. They would feel actual physical strain in the suspense which piles up to the only possible denouement.

There is more than good direction. There are excellent performances by Jean Gabin as the deserting soldier; Michele Morgan as his wide-eyed mistress; and particularly Michele Simon as the pathological toy-merchant who kills and mutilates because of an unnatural love for his ward. In addition, there is an outstanding gallery of minor characters--each strikingly delineated and yet kept in proportion.

This is an unpleasant picture, with suicides, murders, and seductions in plenty. But its grim power is the very thing which makes it exceptional.