I believe that this movie is from the 80s, but it could be late 70s.
2 super powers (I cant remember if they were officially the USA and URSS or just meant to signify them in a near future) decide to solve their conflict by a single confrontation.
Each would select a champion to act as representative in personal combat.
Maybe: The Challenge (1970) – https://archive.org/details/The_Challenge_1970_TV_Movie_Darren_McGavin