MOSCOW, Wednesday -- Twelve thousand Germans fell on the snow-covered battlefield before Moscow yesterday but still the Germans advanced on the city from the north, west and south, and in an accompanying sweep along the Sea of Azov captured the important port of Maviupol, a communique said today.

Kalinin, 100 miles northwest of Moscow, was mentioned for the first time in a Russian communique. It said fighting was especially fierce in that and in the Vyazma and Bryansk sectors, a tacit admission that Moscow was now half encircled, with the Germans battering their way along four main approaches.

Although the Russians did not claim that the drive on Moscow was stopped, they emphasized that the German losses were terrific--almost a division of their men falling dead or wounded in one sector in one day.