It seems quite incompatible with recorded history.
The language used, the political connections drawn and most important: the date alawys used in this unsourced propaganda from anti-communists lessen the probability and plausibility severely.
At the centre of World Revolution, Stalin controlled large funds for communists outside the Soviet Union and guided the theoretical and political aims goals and strategies of those depending on Soviet aid for their political work. And Stalin was in the habit of ordering fierce agitation in opposing countries opposing the Soviet Union ,especially in war, but ordering silence and cooperation in countries allied. This is what happened in Germany from 1939–1941, when the communists of the now dissolved KPD lost incentive to oppose Naziism Nazi-Germany was the friend of the worker's paradise, and after Barbarossa when German communists were again instructed to do the utmost in trying to bring down the fascists.
For the communist party in the US:
The party dropped its peace program and demanded American aid for the Soviet Union and American intervention in the war. After Pearl Harbor, the CPUSA endorsed Roosevelt's war policies, called for a quick American invasion of Europe to relieve Nazi pressure on the Soviets, and vehemently denounced any interference with the war effort as treasonous. These policies allowed the rebuilding of many of the Popular Front relationships destroyed during the period of the Nazi-Soviet Pact. The heroic Soviet resistance to the Nazi army also lessened the pervasive anticommunist sentiment of the American public.
Released from prison in 1942 as a symbol of goodwill toward America's Soviet allies, Earl Browder became convinced that the Soviet Union's wartime alliance with the United States and Great Britain was permanent. Emboldened by the dissolution of the Comintern in 1943, Stalin's gesture to his Western allies, Browder dissolved the CPUSA in 1944 and reformed it as the Communist Political Association, intending to make Communists the left wing of the Democratic party. He announced that socialism would not be on the American agenda in the foreseeable future, a step that disconcerted some members of his own party.
Harvey Klehr, John Earl Haynes, and Fridrikh Igorevich Firsov: "The Secret World of American Communism", Yale University Press: New Haven, London, 1995, p 11.
This is of course circumstantial evidence. Especially in light of the chaotic incompetence of the American communists. Whether there was such a directive given out cannot be excluded completely from the above.
In 1943 Wolfgang Leonhard, a young German attending a Communist International (Comintern)school for foreign Communists near Ufa, a city 750 miles east of Moscow, received an unusual assignment. The Comintern's archives had been transferred to Ufa when the Nazi army was threatening Moscow, and Leonhard was among a group of students given the task of putting the chaotic archives into order. His assignment was to organize the records of the American Communist party. In his memoir written in 1958, a decade after his break with communism, Leonhard noted:
The Communist Party of the U.S.A. was readily conceded first place for chaos and confusion. The sacks belonging to my American comrades contained not only whole bundles of Party documents which had simply been stuffed in without even a file-cover being put round them, but also the remains of cinema advertisements, old numbers of the New York Times, broken pencils and every kind of rubbish that had not the slightest connection with the archives…
There were so many things that I would have liked to have read – protocols of sessions of the Central Committee, struggles with the factions, justifications for the expulsions of leading Party officials-but unfortunately there was not the slightest possibility. I had to open the sacks, put the material in folders, and write on the outside "Trade Union" or "Miscellaneous" or "Party 1921–1923''at the pace of a Stakhanov. With every day that passed, we were urged more and more often to pay less attention to accuracy than to speed.'
ibid, p 4.
But this remote possibility of a subaltern faction giving out this order from the claim, or something resembling it, doesn't alter the fact the the date of 1943, the wording, the strategy outlined and the attribution "communist headquarters" are not plausible.
As this area of investigation was of the highest interest for American anti-communists, some form of evidence should surely be found. What committees and the FBI did find looked like this:
In addition to its investigation of alleged Japanese subversion,
the Committee connected the Japanese problem to the ubiquitous
Communist menace. Basing its conclusions largely on the editorial
policy of the Communist newspaper, The People's Daily World,
the Committee summarized the Communist Party line in 1942:
All Communists are ordered to minimize the Japanese danger. All large
military efforts in the United States must be directed to Europe. Our immediate task is the defeat of Hitler and the protection of the Soviet Union. Smear anyone who advocates major activities against Japan at the present time. Our historic course with Japan will be determined at the conclusion of the war with Germany.
Meanwhile our traditional role as the champion of racial equality must be maintained.26
Fn 26: Second Report, p 60 (Fully cited as: California Legislature, Report: Joint Fact-Finding Committee on Un-American Activities in California. With the report for 1948, substitute "Senate" for "Joint" Fact-Finding Committee. Henceforth to be cited as First Report, Second Report, etc. The reports noted above are: First Report (1943); Second Report (1945); Eleventh Report (1961); Twelfth Report (1963); Thirteenth Report (1965); and Thirteenth Report Supplement (1966).
Robert L. Pritchard: "California Un-American Activities Investigations: Subversion on the Right?", California Historical Society Quarterly, Vol. 49, No. 4 (Dec., 1970), pp. 309-327. (jstor)
Note the date and that it is again an interpretation done by an interested side. Some of these reports are on archive org, and they use the word "smear" a lot. Often it seems as if the meaning has changed.
Apart from the assertion in They Never Said It that
Researchers in the Library of Congress have been unable to locate any such 'directive'; nor do specialists in Soviet affairs regard it as authentic.
We also have to include prosecutors under the Smith act and federal agents to those who were looking to find exactly that kind of evidence:
The FBI had compiled a list of 200,000 persons in its Communist Index; since the CPUSA had only around 32,000 members in 1950, the FBI explained the disparity by asserting that for every official Party member, there were ten persons who were loyal to the CPUSA and ready to carry out its orders.
And this relative amount of infiltration became ever greater, when the CPUSA membership was down to 5000 at the end of the fifties:
Following orders from the Kremlin, Hoover explained, Levison was guiding Dr. King, thus affecting the course of the civil rights movement. In a hearing, he described the party in the United States as “a Trojan Horse of rigidly disciplined fanatics unalterably committed to bring this free nation under the yoke of international communism.” He may well have been jousting with his boss, for the attorney general had recently said that the American Communist party “couldn’t be more feeble and less of a threat, and besides its membership consists largely of FBI agents.” Kennedy had been horrified to discover that Hoover had assigned over one thousand agents to internal security, merely a dozen to organized crime
Curt Gentry: "J. Edgar Hoover: The Man and the Secrets", W. W. Norton & Company, 2001.