"The Seventh Seal." Embassy. $39.95. Ingmar Bergman's 1956 film (most memorable, possibly, for the sequence in which its warrior protagonist tries to stall Death with a game of chess) is dark, medieval, gloomy, obscure, symbolic--pure early Bergman, that is. It is also engrossing and unsettling. It suggests that in film no less than in a novel, a modern man can wrestle with the largest issues of all: life, death, faith, doubt, suffering and pleasure. The cassette form seems ideally suited to one of the rare films that can stand--indeed demands--repeat viewings and thoughtful contemplation. Subtitles.