Three German armies, spearheaded by 2000 tanks, stormed a 100-mile stretch of the Don River Thursday and the Russians met them head-on in probably the greatest armored battle in history which may decide the future course of Hitler's grab for the Caucasus oil lands.

Advancing almost 100 miles southeast from Stary Oskol, whose fall the Russians announced only Wednesday, the Germans reached the vicinity of Rossosh, 210 miles north of Rostov, gateway to the Caucasus.

Two thousand tanks, 1,000 on each side, were reported clashing on one narrow sector around Voronezh amid a bedlam of bursting bombs and shells. The sky was full of planes, as many as 120 German fighters swarming out in a single formation.

The Russians claimed to have littered the Don River banks with wrecked German machines and thousands of dead, and the Germans claimed to have destroyed 289 Russian tanks and to have shot down 75 more Russian planes Wednesday, against only two German planes lost.

Though a lull continued in the main battle for Egypt, British ground and air patrols hammered relentlessly at the hooked, 55-mile line west of El Alamein, where Marshal Erwin Rommel's German Africa Corps was stalled within 65 miles of the Alexandria Naval Base.

Rommel was reported massing strong forces of anti-tank guns and showed no signs of withdrawal, despite his difficult supply problem and the heavy pounding he was taking from the RAF.