The awful tragedy of former Italian Premier Aldo Moro forces attention on the state of the international Communist movement.

It shows how different national conditions shape the party in each country. It demonstrates that the response to those conditions fosters a kind of civil war between moderates and extremists in the Marxist-Leninist camp. It identifies the reason - the Catholic political culture - that has made Italy so vulnerable to the Communists and a principal theater for their civil war.

The national character of different Communist parties strikes even the least sensitive observer. Mao's communism reflected the overwhelming role of the peasant in the population and problems of China. Titoism features the need to balance different ethnic groups in a single state. Castroism has a touch of cha-cha-cha.

Scarcely less well-known is the extent to which the Communist parties have been split by the problems of balancing international revolution against accomodation to various national peculiarities. Divisions along precisely those lines now wrack the parties of France, Czechoslovakia, Hungary, China and Cambodia.

Those national splits have repeatedly bounced back to the very center of Communist power and doctrine. Lenin implicityly, and Stalin explicitly, abandoned revolutionary comrades abroad to promote "socialism in one country." Khrushchev tried to promote Soviet expansionism by dealing with revolutionary nationalists, such as Nasser in Egypt, who were not necessarily pro-Communist. Now Moscow appears to be split between orthodox leaders, supposedly led by the party ideologist Mikhail Suslov, who would discourager "national deviation," and Leonid Brezhnev, the party secretary who is said to be more tolerant.

The Italian Communist Party has not been exempt from any of these experiences. Palmero Togliatti, the party's first postwar leader, developed and the present leader, Enrico Berlingue, deepened an "Italian road to socialism." If featured a mass popular base, alliances with other parties in the parliamentary system and rejection of Russia as a universal model. Important Italian communists, notably Luigi Longo, who suceded Togliatti, preferred a more revolutionary approach - as did Moscow.

But to a degree unknown in any other Western country, the moderate approach paid off. In the 1976 election, the Italian communists won 34.4 per cent of the vote, emerging as the second largest party in the country with control over the town halls in every major city.

Berlinguer moved for a "historic compromise" or coalition with the major party, the Christian Democrats. Of the two Italian governments formed since the election, under the leadership of Premier Mario Andreotti, the first depended upon Communist abstention and the second on Communist support.

It is the Christian Democrats who have made the Communists so successful in Italy - and so unique in the world. Unlike the other major parties governing modern Western countries, they have not been chiefly shaped by liberal ideas. On the contrary, the Christian Democrats have been a by-product of the Catholic church and its special culture.

As a result they did not adjust well to a period of phenomenal economic growth that shifted the bulk of the Italian population off the farms of south to the industrial cities of the north. They have been poor at managing the apparatus of the modern state. In dealing with Communists, they have either gone for outmoded social positions - such as opposition to divorce and abortion - or sought to put them into the system by moving toward the "historic compromise."

The Moro affair tied all these elements together in a single dramatic package. Moro was the chief architect on the Christian Democratic side of accommodation with the Communists. He was kidnapped and murdered by the extreme revolutionary remnant of the Marxist-Leninists in Italy - the Red Brigades, The purpose of the crime was to discredit both the Berlinguer leadership in the Communist Party and those Christian Democrats who were prepared to accept the historic compromise.

Probably the effect will be exactly the opposite. Berlinguer and the Communists have stood up to the Red Brigades and the kidnapping with great force, and look more than ever like a competent party of law and order. The Christian Democrats have shown ineptitude in handling the investigation and division in dealing with the kidnappers. Though nothing is ever ruled out in Italian politics, it is very hard to see how the end of the Moro affair will not be another step toward participation in government by the Italian Communists.