In the USSR, what if any was the formal, ideological response to the Cultural Revolution in China?

There's a PHD thesis and book chapter, both by Elizabeth McGuire on this matter. Soviet reaction was mixed, confused and ambiguous. The Cultural Revolution contained deeply anti-Soviet elements, and accused them of revisionism and deviation from Marxism-Leninism, but it came at a very inopportune time for USSR, which hampered any clear, official response. Because at the time, Brezhnev has just ousted Khruschev and was attempting to undo many of the latter's de-Stalinization (i.e. revisionism), and yet the Cultural Revolution was accusing the USSR of being revisionist. Thus the USSR was stuck between denouncing Khruschev's revisionism and defending itself from China's charges of revisionism. At the same time, China was being roundly criticized and mocked by the West, so attacking China risked being seen as being sympathetic to the West and attacking the shared Marxist-Leninist ideological foundation.

To put it bluntly, the Cultural Revolution is the doing of a madman clinging to power, and had no ideological basis. Mao was threatened by the failed Great Leap Forward and also saw that a USSR-style bureaucracy will easily do away with paramount leaders, no matter how prestigious they are or once were, as Khrushev was. So he leveraged and built on his popular appeal to purge his political enemies. In effect, China was insane during this time. How do you argue with, or defend yourself from criticisms from insanity? One account from a Soviet delegation to China said that, surrounded by red guards chanting anti-Soviet slogans, they tried to respond by singing the Internationale, but the crowd responded by singing The East is Red. The insane are impossible to engage, as they will deny any common ground, and also avoid forming any coherent argument to respond to.

Reaction was understandably muted, and consisted of the following:

• Satire, as one might react to absurdity such as the Cultural Revolution. The aforementioned incident with the Soviet delegation was satirized in the song "Tau Kita" "Tau Ceti" (there is a poor English translation here). Sometimes this ridicule required no effort at all; in 1966 Literaturnaya gazeta ran an article that was a direct reprint from a Chinese paper, about a watermelon salesman who solved the rotting problem by applying Maoist ideology.

• Lamentation. China was once a strong ally of the USSR, having fought a world war together and being the recipient of technologies and expertise. The development was viewed as tragic and impudent, as an inferior giving up Soviet tutelage.

  Komsomol’skaia pravda wistfully lamented their departure: "Now, there is no photograph of the Soviet emblem on the door of number 422."

  This is a way of indirectly criticizing China without being seen as directly attacking an ideological ally.

• Graphic reporting of the atrocities. Soviet papers did not hesitate to report the most gruesome aspects of the Cultural Revolution, such as its torture of even modest individuals obliquely related to the revolution's targets, like Russian language middle-school teachers, and the desecration of symbols of Soviet friendship. Such incidences were meant to repulse the reader without engaging the uncomfortable ideological issues, although this was also risky due to the similarities with Stalinist atrocities, particularly after Brezhnev took power.

• Eventually the USSR did form a coherent argument highlighting the differences between itself and China, although this was done with care since the two were more similar than not. This narrative focused on the Cultural Revolution's driving forces, of students (even non-party members) and the army supporting a single leader outside the party, and the absence of the working class and the party, hence this could not be a true Communist-style revolution. The Cultural Revolution also lead to the formation of a new narrative: that socialism was culturally inclusive, and should celebrate Western cultural legacy, and this stood in stark contrast to the destruction of the Cultural Revolution.

• Another response was patriotism motivated by fear, as incidents such as the Damansky island one stoked fears of Chinese military or ideological attack. Events such as embassy workers being harassed or Chinese tourists vandalizing Lenin's mausoleum were followed by patriotic reports. There were many jokes around this time owing to nervousness of China's numerical superiority:

  How will the war between the USSR and China end? With the unconditional surrender of the USSR after it has taken 400 million Chinese as prisoners of war.

  Such tensions served to unite the left and right elements within Soviet politics against the foreign foe, and helped turn the debate from ideology to patriotism.

Eventually, such reactions, muted as they were, proved fatal to USSR itself since once the foreign boogeyman was gone, the same criticisms could be turned inward to USSR itself, to which there was no good response.