A cautious reaction by Italy's powerful Communist Party to a Soviet attack on Spanish Communist leader Santiago Carrillo, is seen here as the latest indication that the Italian Communists want to avoid a break with the Soviet Union.

The Italian Communists have labeled the attack as overly harsh, sharp and unconstructive as well as misleading on the nature of Eurocommunism.

But these remarks have not been followed by any strong defense of the Spanish leader, causing speculation that the Eurocommunist front made up of the Spanish, French and Italian paites may not be as firm as was previously believed.

In his contention that Soviet society is bureaucratic and oppressive rather than socialist, Carrillo has gone far beyond the position of the Italian Communist Party.That party has gradually begun to criticize some aspects of the Soviet system but has always stopped short of questioning its socialist nature.

The Italian Communists' top spokesmen said this weekend, "We do not intend to take sides" and "We have always followed the rule of not exacerbating conflicts." Their caution reflects in part the fact that last week's attack on Carrillo came at a delicate time.

The party is in the final stages by negotiations among six political parties here for a joint emergency program that it regards as another step in a slow march toward participation in an Italian coalition government.

Party leader Enrico Berlinguer, who four years ago mapped out the party's strategy of seeking a "historic compromise" with Italy's Catholic and Socialists, clearly is not eager for involvement in an ideological dispute that could bring trouble with Moscow.

A break with the Soviet Union now might bolster those with doubts about the Eurocummunist commitment to Western values.

But it also would be extremely unsetting for Italy's Communists, who need their Marxist identity if credibility among party members is to be maintained and if the allegiance of Italy's disaffected leftist youth is to be restored.

Some veteran observers here believe the Italian Communists want to avoid a break with Moscow because they fear the Soviets might eventually give support to the formation of a rival Communist Party here.