The scientists and policymakers who were closest to the bomb's development all worried tremendously that a secret arms race for nuclear weapons (basically unrestricted proliferation) would lead to a wildly dangerous world. So one of the first things they did, even before the bomb was used, was talk about schemes for limiting the future production of nuclear weapons. This was literally one of the first things that Truman was told about the atomic bomb — in an April 1945 meeting with his Secretary of War, the Secretary of War went on at length about how tenuous the American nuclear monopoly was, and how dangerous a multi-nuclear world was.

They called this "international control" — schemes for having the international community cooperate to limit the proliferation of nuclear weapons. The State Department issued a study on the question headed by Dean Acheson and David Lilienthal, with the technical expertise of J. Robert Oppenheimer. The Acheson-Lilienthal Plan concluded that the bomb could be controlled, because it relied on specific raw materials that were then thought to be rather rare (uranium or thorium) and that the factories necessary for turning such raw materials into bomb-grade fuel were large and relatively easy to detect. Control the uranium, and have inspectors look for the factories, and the bomb can't be made in secret.

This got leaked to the press early, and then published, and was taken as "the" US plan, even though it had never really been vetted at the top and there were those who had concerns with it. A version of it was turned into what was called the Baruch Plan and presented to the United Nations at the UN Atomic Energy Commission (not to be confused with the US Atomic Energy Commission, the organization that later took over US bomb production). There were a few changes to the plan when it was presented to the UN, notably a focus on what would happen if someone broke the rules (inspection and enforcement). It also stipulated that the US would not get rid of its existing (small) atomic stockpile until all other countries had fully complied.

These things made it easy for the Soviets to reject the plan, and for people in favor of the plan to argue that Bernard Baruch, and the Truman administration in general, had tried to sabotage it. (I'm dubious of this, because you can't have a real treaty with inspection/enforcement issues wrangled out, because they are at the core of whether it will work or not, but whatever). The Soviets proposed their own counter-plan, one which basically said "atomic bombs are banned as of today," which of course the US also rejected, because it was basically enforced as a matter of good faith (and the US didn't trust the USSR).

So the whole thing stalled. Periodically talks resumed on the issue between 1945-1949 but mostly the US just continued making bombs and within a couple of years the idea of international control seemed increasingly improbable.

We now know, in retrospect, that the Soviets were busily working to make atomic bombs of their own during this period, and would almost surely have never accepted any plan of this sort. When their first bomb was detonated in 1949, and detected by the US shortly thereafter, it effectively scuttled any further attempts at international control.

A version of these plans was later turned into the Nuclear Non-Proliferation Treaty in the 1960s, the main difference between that existing nuclear nations were allowed to keep their arsenals, making it more politically palatable to them.

I have written a bit about the events of 1946 here — it is one of my favorite years, historically, because so much was still up in the air, getting figured out. At the beginning of the year, there was sincere hope that the world would come together to tackle the future threat of nuclear weapons. By the end of the year, almost no one thought that was likely to happen anytime soon.

I would rank the Baruch Plan as a "reasonably sincere effort." None of the major changes from the Acheson-Liliethal Plan were anything other than practical considerations when dealing with a world full of untrustworthy actors. Could they have been down-played, could they have been temporarily ignored to get a working framework in place? Maybe. But issues of inspection and enforcement are important ones, and I think we can be reasonably confident that the Soviet Union would have violated any treaty that did not actually try to hold it to its word. So I don't think they were unreasonable things to bring up at the time, even if it was potentially suspected (e.g. by Baruch) that this would be unacceptable to the Soviets. I have looked through Baruch's papers and never found anything that made me think he, of all people, was cynical about this — he seems to have given it his all. If the Soviets had agreed to it, would the US actually have signed on? No way to say (especially since Congress has to get involved in actual treaties) — maybe, maybe not.