One week before nationwide local elections, Italy's Communist Party has decided to back an attempt by several opposition parties to bring impeachment proceedings against Prime Minister Francesco Cossiga on grounds that the Christian Democratic leader allegedly aided the escape of an Italian terrorist.

The decision by the 30-member directorate of the Communist Party appeared to threaten the stability of Cossiga's two-month old coalition government only days before 43 million Italians go to the polls to elect regional, provincial and city governments.

The question of Cossiga's involvement in a case involving the son of another prominent Christian Democratic politician makes terrorism a prime issue in an election that involves no parliamentary seats but the results of which are considered an important political barometer.

In the past the Christian Democrats have used left-wing terrorism as a campaign issue against the Communists. This time, the Communists appear determined to get the most political mileage possible out of a terrorist skeleton in a Christian Democratic closet.

On Saturday, a parliamentary commission narrowly absolved Cossiga of charges that he indirectly helped Marco Donat-Cattin, 28, the son of the deputy secretary of the Christian Democratic Party, Carlo Donat-Cattin, in avoiding arrest on charges that he belonged to the Front Line terrorist group.

The 11-to-9 vote along strict party lines came after the commission heard testimony from Donat-Cattin, Cossiga and an accused terrorist.

Roberto Sandalo, 26, a friend of Mrco Donat-Cattin, insists Carlo Donat-Cattin asked him to warn his son of his impending arrest after being tipped off by Cossiga. Cossiga admits he met with Donat-Cattin, but denies he revealed any official secrets.

According to parliamentary rules, the narrow vote was insufficient to permanently close the case. If 318 members of parliament sign a petition, the case could be reopened when the parliament reconvenes June 10.