Both the USA and USSR were aware of the failure of the Great Leap Forward. But, first we have to put these events in historical context. We can't really understand the response to an event without fully understanding the event itself. (Apologies in advance, but I am not going to put sources in this answer. If anybody finds something questionable, I am more than happy to provide a citation.)

1. The End of the Qing and the Republic of China:

Two things to keep in mind throughout:

1. the Qing were foreigners (from Manchuria);
2. ethnic ties are important.

Our story starts in the year 1796. The British had just dispatched a mission under Macartney to bring China into the Westphalian international system (establish reciprocal embassies, formal acceptance of equality and sovereignty, etc.) as well as achieve certain trade goals. The Emperor denied all of the British's requests: the Chinese emperor, at this point, still has a belief in China's superiority over all other powers, the will to reject British demands, and a belief that the British had nothing the Chinese needed. Over the next century or so, this thought process would dramatically change.

In 1799, the Qianlong Emperor dies and is succeeded first by the Jiaqing Emperor and then by the Daoguang Emperor (these two rulers had power from 179 to around 1850). Under their reins, there were rebellions - the White Lotus and Taiping are the two most prominent ones - that significantly weakened the Qing Empire politically, economically and militarily, a depression - the aptly named Daoguang Depression (scholars disagree about its severity) - and the Opium War (which the Qing lost.)

These events together accomplished three things:

1. exposed just how internally weak the Chinese political system was by this point by (a) demonstrating just how powerful opposition to the regime was (I recognize that the White Lotus and Taiping rebels eventually lost, they were still powerful);
2. exposed just how externally weak China had become: the sense of superiority was undermined by losses in the Opium Wars;
3. exposed potential fragilities in the Chinese economy.

Overall, in 50+ years, the Chinese went from being able to unilaterally reject - rather fair - terms presented by the British to losing the Opium Wars and having terms 'shoved down their throats.'

Some very interesting things occurred, but to fast forward a few decades, China could no longer claim it was the most powerful country in the world (they had just lost to the west during the Opium Wars), but at least it was the most powerful country in Asia, right?

In 1895, there was a war between the Qing and Japanese empires. Long story short, the Japanese won. China had officially taken the position as the "sick man of Asia." China, once the most powerful country in the world, had fallen to being one of the weakest powers. Two sides emerged: one group blamed foreign ideas, influences, and people for Chinese collapse, the other blamed China's traditions and institutions which constrained the growth of China's economy (long recognized as a prerequisite for political power -- the Salt and Iron Discourses provides some interesting background.) The 100 Days of Reform and Boxer Rebellion resulted (note: these events are much more complicated then the description I will provide.)

In a nutshell, the 100 Days of Reform was an attempt to modernize China's economy and political system. The Boxer Rebellion was a backlash against foreign influences (the Manchu's, by some boxers, were considered foreign. Qing-Boxer politics was by no means cut and dry.) There are some rather interesting parallels between how Cixi viewed the Boxers/west and how Chiang Kai-Shek viewed the communists/Japanese.

Here's where we are: there are two camps - those who believe china is best served by adopting western ideas, technology and customs and the strict conservatives. The Chinese communists were more a fusion of these two camps: adopt the west's technology, but reject the political systems of both camps. The Great Leap Forward takes this to an extreme. Chinese politics between 1911 and 1949 quite important, but I'm going to skip forward 50 some odd years.

Great Leap Forward: Background

The GLF was an attempt to quickly create communes and boost steel production such that china surpasses Britain in 15 years. It failed for a variety of reasons. What you should recognize is the goal: "make china great again" (this slogan, if you will, underlies most actions taken since 1895.) Many people saw this as the best way forward...

Reactions:

The USSR under Khrushchev reacted prior to the reforms and denounced the GLF. That among with other actions (skirmishes with Taiwan) led to an extreme breakdown in ties to the point where all Soviet support to china was withdrawn and the USSR amassed an army on China's borders. While ideology was important, there was also (flawed) political reasoning. The Soviets never expected the US to "ally" with China and wanted China to remain weakened - they did not want a strong communist state which disagreed with them ideologically.

The US public reacted with horror (famine will do that). However, the breakdown of Sino-Soviet relations presented an opportunity, one which would be realized by Henry Kissinger and Richard Nixon. At the time, however, there was not much that the US could really do. It was not as if the US and China were partners or that the US had the means to stop the GLF absent the use of force which would not have gone well. See the Korean War for more details. It wasn't as if the Chinese military was advanced, but occupying and controlling a unified country with China's population is quite difficult.

Chinese weakness -> communists and GLF -> Sino-Soviet split -> Warming of US and Chinese ties.