Moscow — The Soviet government has mounted its most energetic antismoking campaign ever, including a ban of smoking in offices. Soviet President Leonid Brezhnev signed a decree of the Communist Party Central Committee and the Council of Ministers calling for "systematic explanatory work among the population about the harmful influence of smoking, aimed at gradually getting rid of the habit." It calls for "measures for the limitation, and in the future, the ban of smoking in working places, providing special rooms for smoking." Radio and television will also air programs dramatizing the dangers of cigarettes. But perhaps the best weapon in the antismoking arsenal is the signature of Mr. Brezhnev, who has tried repeatedly and unsuccessfully to break his chain smoking habit.