Moscow's angry near-excommunication of the Italian Communist Party may hold important minuses as well as pluses for the Western alliance.
The two main dangers are that this latest breach between the Kremlin and the biggest communist party in West Europe will:
1. Make the Italian Communists more acceptable than before as a partner in a coalition government with either the Christian Democrats or the Socialists.
2. Help spur a revival of the ''Eurocommunism'' of the 1970's whereby some Western communist parties renounced Moscow's automatic leadership and pledged to abide by Western parliamentary practice.
If these dangers are realized, this is likely in turn to provoke yet further contention between the Reagan administration and some of its most important European allies.
True, Washington has taken in its stride the presence of four Communist ministers - and pro-Moscow Communists at that - in France's Socialist government. But they are there on President Mitterrand's terms as very junior partners. Further, there is evidence that communist appeal in France is waning - partly because the French Communists continue to support the military crackdown in Poland.
Although the French Communists are the first to actually make it into government since the emergence of Eurocommunism as a phenomenon, they were never the pacesetters for it. That role was left to the Spanish and Italian communist parties - particularly the latter.
At no time have the French Communists allowed a really major breach to open between themselves and Moscow. The Spaniards and the Italians, on the other hand , have never minced their words in their disagreements with the Soviet Union.
So it has been over recent events in Poland. And the disarray of feuding communist party comrades, with its disillusionment for watching Europeans, provides the West with its most obvious pluses.
Spanish Communist leader Santiago Carrillo commented bluntly Jan. 11: ''The organization of the workers' revolutionary movement around the Soviet Union is dead once and for all. We must move toward an international alignment going beyond the historical dividing line between socialists and communists and taking in the liberation movements of the third world.''
So far, Moscow has virtually ignored Mr. Carrillo. Presumably the Soviet theorists recognize that the Spanish Communist Party is only a minor force in that country's politics. It is hardly likely to be taken into government when the thought even of Spain's democratic Socialists - the main opposition party - assuming power is enough to raise fear of a right-wing Army coup.
In Italy, the situation is quite different.
First, the Communists are the second biggest party (after what the London weekly, the Economist, calls the ''bloated'' Christian Democrats). They are the main opposition party of the left, polling nearly three times as many votes as the Socialists in the last general election.
Second, Italy's armed forces are basically apolitical (although they include an occasionally wild right-winger near the top).
And third, the possible inclusion of Communists in government has been an intermittent topic of debate for a decade or more. It had already surfaced again with the prospect of an early general election later this year.
Some outsiders might have thought the possibility of communists reaching positions of power in Italy would have pleased Moscow and led the Soviet theoreticians to handle the Italian Communists with kid gloves. This has not been the case.
Perhaps from the Soviets' point of view, Italian Communist leader Enrico Berlinguer left them no alternative. He was prompter and sterner than some Western democratic leaders in denouncing military repression in Poland. The Soviet Communist Party, he subsequently charged, ''had stood Marx's philosophical innovation on its head.''
In its place, he argued, the Soviets had introduced ''a sort of ideological credo called Marxism-Leninism, conceived of as a corpus of ossified doctrine'' aimed at guaranteeing a single type of economic-political structure that could be imposed on utterly differing situations.
The Soviet party newspaper, Pravda, lashed back Jan. 24 - choosing the Italian party's central committee rather than Mr. Berlinguer as its target. The Italian party committee's criticism of Soviet policy, the newspaper charged, ''was very much reminiscent of and sometimes directly coincided with the utterances'' of US Secretary of State Alexander Haig.
''What does all this mean?'' Pravda asked. ''Whose class interest does all this serve? In today's world, this means direct aid to imperialism. . . This means aid to anti-communism and to all forces hostile to the cause of social progress in general.''
The Italian Communist Party is answering back. The Jan. 25 edition of the party newspaper, Unita, carried the Pravda editorial in full and promised a full rebuttal in the next day's issue.
''We must initially remark,'' Unita said, that the way the (Pravda) article was introduced, its argument and tone, show that its authors are absolutely incapable of conducting a discussion on a basis of parity and reciprocal respect.''
In the meantime, the Socialists' ambitious and tactically clever leader, Bettino Craxi, is probably already weighing how all this might improve the outlook for a Socialist-Communist coalition after the next election - under his premiership, of course.
The only snag is that Moscow's infuriated attack on the Italian Communists might persuade some Christian Democrats that they should explore beating Mr. Craxi in the coalition game - directly or indirectly. That might help them regain the premiership, now held by a Republican.
If either politician succeeds in building such a coalition, however, he is likely to raise the hackles of the Reagan administration. Italian-American relations would probably head through some rough waters. And broader transatlantic ties would also be embroiled since other West European governments , notably that in France, would probably come to the support of the Italian coalition experiment.