First off, it wasn't only the United States to help the Soviets, but also the United Kingdom and Canada. It's also often overlooked that both of the latter contributed much, much more to the Eastern Front.

Here is what Britain supplied to the Soviet Union;

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• 3,000+ Hurricanes
• 4,000+ other aircraft
• 27 naval vessels
• 5,218 tanks (including 1,380 Valentines from Canada)
• 5,000+ anti-tank guns
• 4,020 ambulances and trucks
• 323 machinery trucks (mobile vehicle workshops equipped with generators and all the welding and power tools required to perform heavy servicing)
• 1,212 Universal Carriers and Loyd Carriers (with another 1,348 from Canada)
• 1,721 motorcycles
• £1.15bn worth of aircraft engines
• 1,474 radar sets
• 4,338 radio sets
• 600 naval radar and sonar sets
• Hundreds of naval guns
• 15 million pairs of boots

In total 4 million tonnes of war material including food and medical supplies were delivered. The munitions totaled £308m (not including naval munitions supplied), the food and raw materials totaled £120m in 1946 index. In accordance with the Anglo-Soviet Military Supplies Agreement of 27 June 1942, military aid sent from Britain to the Soviet Union during the war was entirely free of charge.

The British high command, seeing the Germans coming closer and closer to Moscow, decided to give Russia tanks, even though those were desperately needed in the Pacific. In fact, the reason why Malaysia and Singapore were in danger was because British-supplied tanks from the colonies made up 40% of all Soviet tanks that took part in the Battle of Moscow.

Sorry, I had to get that off my chest to answer the question. The answer is (comparing to Britain) "important, but not as important"

The US was busy in the Pacific, so there's a reason why they weren't able to offer as much help.