In 1938 Stalin proposed G.M. Malenkov as the Head of the NKVD, however "a majority of the Politburo recommended L.P. Beria for the post"(Getty, Manning). Does this event indicate that Stalin was actually not in control of the party?

You refer to the article "Narkom Ezhov" by Boris Starkov. If Starkov’s information is correct, the political history of the 30s requires a serious reassessment. However, so far, there seems to be no reason to rush into this.

First of all, about the “source” itself - Starkov’s article. The sensational fact about the confrontation between Stalin and his associates regarding the appointment of Malenkov was stated by the author succinctly, without any explanation. Sources (as in most other cases) cannot be verified: “Archive of the General Department of the CPSU Central Committee. Materials of the Secretariat of the Central Committee of the All-Union Communist Party of Bolsheviks, November-December 1938. See also M.I. Kalinin on the party asset of the NKVD in December 1938 - TsGAOOR. Materials of the party asset of the NKVD of the USSR December 1938 - January 1939. "

Unverifiable sources (or even their complete absence) in Russian works on the history of Soviet society are a sad pattern, caused not necessarily by the malicious intent of the authors, but by the rules of access to Russian archives. The scientific cost of this is obvious and once again confirmed in this case. Historians are deprived of the opportunity to verify the correct interpretation of the document by a colleague, and therefore can not lead a normal discussion. The only way to at least partially overcome this is to fully disclose the content of the documents on the basis of which the corresponding conclusions are drawn. Starkov’s article does not do this. The value of these evidence by Starkov is also diminished by the fact that they coexist in his article with data that never received clear documentary evidence (for example, N.G. Kaminsky and I.A. Pyatnitsky's speech at the plenums of the Central Committee against terror).

Indirect evidence of Stalin's plans to replace Yezhov with Beria is the fact that in the summer of 1938, Beria was transferred from Tbilisi to Moscow and was appointed First Deputy Chairman of the NKVD.

Source: Khlevniuk, Oleg. Politburo: Mekhanismy politicheskoi vlasti v 30e gody [Politburo: Mechanisms of Political Power in the 1930s]. Moscow: ROSSPEN, 1996.

Edit: "Unverifiable sources" fits better, yes.