US capability to deliver atomic weapons to USSR in 1948 was very very limited as many previous threads have demonstrated. Likewise, even for all the deficiencies of the Soviet Army, numbers count and the allied forces (no NATO in 1948) in Germany/Western Europe were not only small, but were not set up with good interoperability, common codes, even common ammo & filler lines for fuel, vehicle electrical systems that would let a US vehicle give a jump to a Brit vehicle with a dead battery, etc.
Having said that, after initial advances the Soviets get trashed...and in 1948 you'd have significant resistance forces operating against them in Poland, Hungary, Ukraine, Baltic States. And in 1948 the USSR had not recovered from WW2 with industrial plant & food production (and manpower).
BTW in 1948, especially since Chinese Civil War not really over, US gets free ride attacking Soviet far east...