By the time the Cold War was heating up FDR was already very sick and his head was not really in the game. He understood most of what the Soviets were about and how to deal with them diplomatically, but by the time the Yalta Conference took place he just wasn't himself anymore. Truman was kind of clumsy in my opinion, at least in the beginning at Potsdam when he gave away our nuclear secret without any need to do so, or any reward or advantage for doing so.
He learned quickly though, and after Greece and Turkey and Kennan's Long Telegram, he reacted with a policy of containment at Berlin and elsewhere that was ultimately successful.
I don't think you can really criticize either man's policy. They were both right for their time.
During World War II, it would have been crazy for FDR to treat the Soviet Union like an enemy. Germany was clearly a major threat to the world order and the Soviets were a hugely useful ally. I suppose you could say he gave them too much at Yalta, for example, but we really needed them against Germany.
Truman was surely right to start trying to contain the Soviets. After WWII ended, they were clearly going to be an enemy and we could not have continued to treat them as if they were allies.
Franklin D Roosevelt was president of USA from 1933 to 1944 and Harry S Truman, who was vice-president under Roosevelt, became president in 1944 after death of Roosevelt. It is not possible to compare policies of Roosevelt and Truman towards USSR as the conditions in the world as well as political position of USSR were poles apart during the president ship of these two president.
FDR was president during period before World War II, and at a time when the world as well as USA was struggling to overcome a severe world wide depression. At this time USSR, after the revolution was still in the process of consolidating its existence as a communist country, which at that time was a very new concept. Once the World War II started the world situation changed drastically and all foreign policies of USA, USSR and many other allied countries had to focus on winning the war to exclusion of other issues. This was not the time for USA to emphasize the difference with USSR. The right approach was to follow a policy of cooperation and collaboration.
The Regime of Truman was mostly the post war period, marked by intense rivalry between USA and USSR called cold war. This was the period when There was a big threat perceived from USSR as a country trying to dominate the world. The requirement of this time was to keep the power and influence of USSR under check.
I believe that both Roosevelt and Truman followed policies toward USSR which were by and large appropriate for the need of their time. And Policies of both these presidents were appropriate in spite of being very different.