On film: '20s actress and '80s critic; Sayre recaptures '50s; Running Time: Films of the Cold War, by Nora Sayre. New York: The Dial Press. 246 pp. $17.95.

''I was first propelled back to the Fifties by recalling the fears and inhibitions of that era during the final spasms of the Sixties,'' Nora Sayre writes. Her retrospective point of view is all the more interesting because she sees that period through the eyes of a woman of today. An ex-film critic, now a teacher at Columbia University, Nora Sayre interviewed directors, among them Benedek, Foreman, Kazan, Polonsky; writers like Arthur Miller; and actors and actresses, like Betsy Blair, of the most significant films of the '50s.

Political implications, as well as obvious and hidden messages, are decoded by in-depth analysis of the films and stories about their making. The author's sharp mind, her incisive and sometimes cruel humor, are big assets here.

Nora Sayre writes: ''Outside of the university, we don't respect our history, as Europeans do. Our talent is for living in the present.'' But she is brilliant in describing the social films (''On the Waterfront''), in reasserting the influence of the blacklist, in understanding the anti-communist films, in deflating the biblical epics. Her analysis of the Martian invaders' vogue invites a comparison with the 'E.T.' craze: What are we afraid of when we welcome those alien creatures?

Nora Sayre's book is a highly rewarding invitation to look back at our recent past, to reevaluate its film production, and to analyze our present cinematographic fads.