The main attempt was to keep the communist countries isolated. The US did not want communism to spread to other countries, so they barricaded the communist countries in and limited trade to and from those countries, basically starving them into democracies.
The United states had been an empire for nearly half a century by the time we went to war with Germany, and after the war it was a superpower. The Soviet Union was its only major competition at that point, and the Cold War was inevitable in my opinion. So, to answer your question, yes, US policy was primarily motivated by an effort to contain Soviet power and influence, and to extend American power and influence. Policies such as the Marshall Plan, while certinaly humanitarian and positive in effect, would most likely not have been undertaken if there was not a communist threat in postwar Europe.
U.S. policy in Europe at the end of the war was basically an attempt to contain the spread of communism. The U.S. and Soviet Union had been uncomfortable allies from the beginning, forced together by Hitler's treachery. There was never trust on either side; and at the end of the war, each side believed the other was attempting to dominate world politics.
The United States did make every attempt to prevent Soviet domination of Europe; as is evidenced by the Berlin Air Lift and the Truman Doctrine. Still, to state that the U.S. opposition to communist aggression was an attempt to "establish power" is something of a non sequitur.
I don't think the two parts of your post necessarily go together. I think that the US was trying to prevent the Soviets from dominating all of Europe, but it does not necessarily follow that the US was also trying to establish its own power. I think we can see proof of this in the fact that the US did not try to truly control the Western European nations. They allowed the French, for example, to go their own way. They did not resist (and in fact pushed) the rise of a strong West Germany. These were not the actions of a country looking for power, even if they were the actions of a country looking to prevent another (the USSR) from getting power.