With a POD of divergence in 1930, I'd say that it is possible. The Nazis haven't risen yet, the Great Depression is in full force, etc. The USA is weak at this point.
Not really. The Soviet Pacific fleet is tiny, the US and Japanese fleets are large, and supplying Soviet forces in Alaska would be virtually impossible. In the event of a US-Soviet war the Japanese would be almost certain to take advantage of Soviet weakness; they're supreme opportunists.
Even given the Depression (which is not yet in full force; that didn't happen until 1932-33) the US is not weak, not compared to the forces the Soviets could actually bring to bear. If war came the US military and supporting industry would be rapidly expanded, to the benefit of the economy; IOTL it was the buildup of US forces and war industry prior to WW II which jump-started the economy and pulled it out of the Depression.
The rise of the Nazis is neither here nor there; Germany in 1930 is not a credible threat to either the Soviets or the US. IOTL it did not become one until after the fall of France ten years later.
Any initial Soviet successes would be reversed within a year or two, after the expanded US forces are brought to bear. That does not mean the Soviet Union would be overrun, though; even if the US repays the Soviet invasion by invading Siberia they can't advance much further than the coast; the logistics won't support an advance into the interior, and the US will be looking over their shoulder at the Japanese as well. The US might take some islands and maybe a bit of Kamchatka, but even that last isn't really tenable.
The fact is that even in 1930 neither is in a position to really harm the other; and given the threats eventually posed by Germany and Japan that was probably for the best.