Checking the IMDB cast list, it's difficult to know who played this character.
Millard Mitchell.
He was only 49-50 and died the October of 53'-the yr the film was released.He looked a lot older
He's very good as the commanding officer in post-war Berlin in "A Foreign Affair". (Made a few years earlier.)
He also played General Pritchard, General Savage's (Gregory Peck) boss in "12 O'Clock High" in 1949.The best diplomat I know is a fully charged phaser bank.