The Italian Communist Party made a significant overture to Italy's Catholics this week in what some are calling the party's most comprehensive statement on religion and atheism in more than a decade.

In a 13-page letter to a progressive Italian bishop, Msgr. Luigi Bettazzi of Ivrea, party leader Enrico Berlinguer criticized the ideological intolerance of some Eastern European countries and denied that his own Italian party professes Marxist ideology as a materialistic and atheistic philosophy."

Observers here believe that the Berlinguer letter is an attempt to reassure Catholics about Communist intentions while the International Synod, meeting in Rome, is discussing the issue of human rights, and when Italian bishops are worried about the future of Catholic educational and welfare organizations here. Sensitive issues like abortion and revision of the 1929 Concordat governing church-state relations in Italy are also on the political agenda here.

The letter, which was published in the party weekly, Rinascita, is a response to a July 1976 letter to Berlinguer from Betazzi. Only a few weeks after the Communists had won huge gains in national elections, the prelate expressed concern over the Communist Party's "Marxist inspiration."

Berlinguer's answer more than 14 months later comes at a time when Roman Catholics have been showing concern over relations with Marxists in Italy and elsewhere.

Betazzi wrote that he was worried about "Your Marxist inspiration which on the one hand is linked to materialism and atheism and on the other is all too often open to dictatorships and violence, even of an anti-religious nature."

Berlinguer's response emphasized an article of the party's statute according to which all those who accept its political program regardless "of their religious faith and philosophical convictions" can be members. It added that the party is not atheistic.

Berlinguer, whose wife is a practicing Catholic, also reassured Italy's bishops that the party did not intend to treat Catholic educational and welfare organizations as "enemy bodies." The Italian Conference of Bishops had recently expressed concern that a new regional decentralization law would imperil such organizations in Italy's six "red regions," with Communist local officials.

The Italian Communist leader said the party was not interested in an Italian state that would give preference to any particular ideology or to atheism.

A Vatican spokesman declined to comment on the Berlinguer-Bettazzi exchange.

The Italian Communist Party has 1.8 million members. In the June 1973 elections it received the votes of another 10 million persons, few of whom are either atheists of Marxists.