Raymond Aron back in the 1950's (in *The Century of Total War*, pp. 152-3) gave an interesting analysis of the inevitability (as he saw it) of Soviet rejection of the Baruch Plan:
"The guiding idea of the Baruch plan was the creation of an international agency for atomic energy, which was to exercise the rights of ownership, management, control, and supervision over the uranium mines and the industrial installations. Such an agency would have enjoyed a kind of extraterritoriality; it would have claimed the privilege of freedom of movement for its officials, of freedom of flight for its airplanes assigned to make aerial photographs, and so on. What chance was there, from the very outset, that the Soviet Union would accept such a concept?
"The first stage of that international experiment would have been a census of uranium deposits and installations processing the fissionable material. Such a census would have enabled the outer world to penetrate the mystery with which the Soviet authorities surround the distribution of their industrial plant. How could a regime that regards every foreigner as suspect, and treats as state secrets most statistics which are published in other countries, be expected suddenly to throw open its territory to international officials--superspies in Stalin's view?
"Let us even suppose the first obstacle actually overcome. The international agency would thereafter have sole responsibility for atomic science and industry. It would partition the installations considered to be dangerous (that is to say, carrying out the operations or processing the materials that might be associated with the manufacture of bombs) according to quotas established with a view to maintaining a sort of strategic equilibrium. It would grant licenses for non-dangerous installations, using "denatured" fissionable materials, in accordance with the economic needs of the various countries. Once more, we ask: By what miracle would the leaders of a state bearing a revolutionary message have agreed that the development of a perhaps
decisive industry be submitted to the authority of an international agency on which "capitalist" states would always have a majority?
"Whether one likes it or not, the Baruch plan infringed on two cardinal principles of the Soviet regime: industrial secrecy, and absolute sovereignty. The Stalinists find it somewhat irritating to have to put up with the presence of foreign diplomats on the soil of Holy Russia. They had no intention of putting up with the presence of "atomic scientists," whose privileges would have exceeded considerably those enjoyed by diplomats."
Arnold Offner, *Another Such Victory: President Truman and the Cold War, 1945-1953*, pp. 150-1, provides some confirmation that these considerations were indeed very much present on the Soviet side, OTOH, he also shows that it is possible that Aron put too much emphasis on the distinctive nature of the Stalinist system in explaining Soviet rejection, inasmuch as Dean Rusk would later admit that the US in the USSR's place would probably have done the same thing:
"But privately, on October 12 [1946] the Soviet scientists on the committee wrote Molotov that the Baruch Plan would mean permitting an international organization, likely U.S.-dominated, to control or inspect all aspects of Russian atomic production and resources. The Russian scientists rejected this in favor of first catching up to America's atomic productive capacity before allowing inspection and control. At the UN General Assembly in New York on October 29, Molotov attacked the Baruch Plan as seeking to preserve America's "monopolistic possession" of the atomic bomb..."
"Surely Russian insistence on immediate destruction and outlawry of all atomic weapons was self-serving because it ended their atomic disadvantage at once and at no cost. At the same time, they sought to preserve their veto and a large, if overestimated, conventional force. More important, as David Holloway has said, neither Stalin nor Truman saw the bomb as a common danger to the human race, although Stalin saw the U.S. monopoly as a threat that could be countered only by building a Soviet bomb. The Soviets also had reason to oppose the Baruch plan, which underscored their atomic disadvantage and vulnerability to sanctions and denied them a veto in the UN, which they believed the US controlled. They were also unlikely to agree to the extensive inspection of their resources and facilities that the Baruch plan portended. Nonetheless, as Dean Rusk, then a junior member of the Truman administration--and secretary of state in the 1960s--reflected four decades
later, if the U.S. and Soviet positions had been reversed in 1946 with respect to atomic power, it is doubtful that the Americans would have agreed to a Soviet-style Baruch plan. Thus it is not surprising, to use Truman's words at Tiptonville in October 1945, that the Russians elected to "catch up on their own hook.""
http://books.google.com/books?id=P5tbHSsBS-AC&pg=PA150
Remember that this was before the UN was flooded with newly independent "non-aligned" African and Asian nations. As of 1946, the UN consisted mainly of the US, western Europe, the "white" British dominions, and Latin American countries which generally took the US side, at least against the Soviet Union. The only reliable votes the Soviets had, besides their own, were of the east European "people's democracies" and these were heavily outnumbered. Hence, Soviet suspicion of any international agency on which they did not have a veto power was unsurprising. Again, try to imagine the shoe on the other foot: a US trying to catch up with the Soviet Union in atomic weaponry would be unlikely to leave its efforts at the mercy of a UN dominated by the USSR and its allies.