"A story of the United States under atomic attack. A tale of two cities, one without a civil defense organization, one with a civil defense organization." Produced by ABC and the Federal Civil Defense Organization.
Starring Orson Welles, Mona Freeman, Marshall Thompson. Adapted from the novel by Philip Wylie (famous sci-fi author and pundit who also wrote "Generation of Vipers").
I'm pulling this from archive.org, so I assume it's public domain.