Question

What is the main idea that the soviet diplomat is presenting in this passage?

Answer 1

A)The US is planning to start a war with the Soviets.

Answer 2

You didn't provide the passage that gives the context of your question.  But I suspect the answer you're looking for, based on a question I've seend elsewhere, is:

The United States is planning on dominating the world economy.

Here's context for that:

Soviet ambassador to the United States, Nikolai Novikov, accused the Americans of imperialism as the essence of their foreign policy, in a telegram he sent sent to the Soviet leadership in September, 1946.  In that telegram, sent about a year after the end of World War II, Ambassador Novikov said:  

• Europe has come out of the war with a completely dislocated economy, and the economic devastation that occurred in the course of the war cannot be overcome in a short time. All of the countries of Europe and Asia are experiencing a colossal need for consumer goods, industrial and transportation equipment, etc. Such a situation provides American monopolistic capital with prospects for enormous shipments of goods and the importation of capital into these countries -- a circumstance that would permit it to infiltrate their national economies.   Such a development would mean a serious strengthening of the economic position of the United States in the whole world and would be a stage on the road to world domination by the United States.

Novikov's telegram was much longer than that, but those lines give you a glimpse of his accusations about US economic imperialism.