The Kremlin virtually excommunicated the leaders of the Italian Communist Party from the world communist movement today by accusing them of having renounced Marxism-Leninism as well as "everything that links them" to other communist parties, thus rendering "direct aid to imperialism."

A Soviet Communist Party statement accused the Italian Communist leaders of "monstrous" and "truly sacrilegious" positions taken since the Dec. 13 military crackdown in Poland. It singled out Enrico Berlinguer, the party's general secretary, and three other members of its leadership, Pietro Ingrao, Giorgio Napolitano and Alfredo Reihlin.

The Soviet stand against the Italian party, the largest in the West, was expected to produce a new debate in the world communist movement.

In Rome Sunday, the Italian party defended its policies, calling the Soviet attack "full of insults and aggression," in the words of Gian Carlo Pajetta, head of the international affairs department of the party. The Soviets have "dared to use insults and attacks that we consider impossible to accept between comrades," Pajetta said, according to Reuter news agency.

The 2,500-word statement issued today was similar in tone and content to major Soviet ideological pronouncements such as the 1948 excommunication of Marshal Tito of Yugoslavia and the subsequent rift that opened with China in the early 1960s.

Today's statement said the Italian Communist leaders in recent years have stated their "special position" on various problems, advancing the notions of "Eurocommunism," "the alliance of Euroleftists" and the "third way" to socialism.

"The essence of these positions consisted, as now can be seen, in gradual departure from the Marxist-Leninist platform," the statement said. "Judging from everything, all these cunning theoretical and political 'innovations' used by its representatives were designed to obscure this renunciation and to conceal its essence from the working class and the Communists" of Italy.

The Italian party's criticism of repression in Poland and the decisions taken by its Central Committee last week "mean that its leaders now openly renounce everything that linked them with the front-line champions of peace and socialism in almost 90 countries and that they openly come out against world socialism," the Soviet party said.

"This means direct aid to imperialism, which has been seeking for decades to weaken socialism and to undermine it ideologically. This means aid to anticommunism and to all forces hostile to the cause of social progress."

The statement, published in the official party newspaper Pravda, said these positions constituted a blow to the Italian Communist Party because they "run counter to the interests of peace, the interests of socialism."

In an apparently direct appeal to the Italian party's rank and file and Italy's working class, the Soviet party asserted that "their most reliable support is the hand of the friend--the Soviet Union, the Soviet Communist Party, the socialist community and the world communist movement."

Today's statement appears to be the climax of a long ideological struggle between the Kremlin and the Italian party over a new and more modern mode of communism championed by the Italians.

East European observers here interpreted the Soviet statement as opening a virtually unbridgeable chasm between Moscow and the Italian party leadership. The Soviets were careful, however, to confine their criticism to "the leaders," presumably expecting to gain support from the party rank and file.

Accusing the Italian leaders of supporting "the right-wing extremists" in Poland's now-suspended independent Solidarity trade union federation, the Soviets said they had used the Polish crisis as a pretext for advancing views "opposed on all the major issues to the policy of the Soviet Communist Party and the countries of the socialist community."

The Italian leaders, the statement said, "subjected to criticism in bad faith, to inadmissible and unjust denigration" the Soviet model of building socialism.

The Italians have condemned the Polish crackdown as reflecting a crisis of the system, which they said was exhausted. They called for new ways of restoring impetus "to the struggle for democracy and socialism."

What the Italians proposed, the Soviet statement said, "is rather pretentious and, let it be said, abstract concepts about a new way to socialism," which was "akin to those tenets of opportunism and revisionism" already discarded by the Moscow-led communist movement.

The Soviets harshly assailed Italian contentions that there was no difference in the foreign policies of the United States and the Soviet Union and also attacked critical implications about a Soviet military buildup.

"To whitewash an enemy is to aid it at a time when the stark and tangible reality demands that the real face of NATO be revealed along with its endless military preparations carrying the threat of a thermonuclear world catastrophe," the Soviet statement said.

"Now, such calumnious assertions have found their way into the documents of the Italian Communist Party."

It added that "not a single Soviet man" can hide "his indignation over an Italian Communist leader's statement that speaks about some hegemonist intentions of our country or its attempts to impose its will on other peoples."

"The positions taken by the Italian Communist leaders amount to nothing else but a serious blow to the people's struggle for peace and against the threat of war, and to an attempt to weaken the influence on the course of international events" of the socialist countries, the statement said.