At the Paris Theater, an uncommonly engrossing and wise new German movie, "A Free Woman," records the losing battle a divorced woman in her thirties fights in Munich to attain belated self-fulfillment. The die is cast in a briskly impersonal society geared to male dominance and early training for career women. This attractive, capable young woman, needing love and encouragement, determinedly sidesteps her former slot of housewife, studies voice and dance, takes on subordinate jobs and painfully maneuvers with her former husband (a cold fish who shrewdly remarries) for child custody. All this is quietly and beautifully projected by an unobtrusive camera and stunningly personified by the feeling, low-key performance of Margarethe von Trotta in the central role. The blond star also happens to be the wife of the gifted director, Volker Schlondorff, as well as his co-screen writer. They and the other performers and contributors have forged a fine, thoughtful and stimulating film that observantly mirrors a human condition, the traditional subordination of women with truthful, biting irony. It would be hard to find a more persuasive and appealing proponent of feminism than Mrs. Schlondorff.