The Italian parliament made another major break from the traditional influence of the Roman Catholic Church yesterday by approving one of the most liberal abortion bills in Western Europe.

With its provisions for free abortion on demand, the new law is bound to have a major impact on Italian society.

The final passage of a bill which has threatened this country's political stability for at least three years came last night with a vote of 160 to 148 in the Senate. The bill was approved by the Chamber of Deputies, the parliament's lower house, a month ago by a vote of 308 to 275.

The bill will radically changed conditions in a country where church influence has hampered the spread of birth control and where illegal abortions are thought to at least equal the country's 781,570 annual live births.

Some pro-abortion groups have estimated that the number of illegal abortions each year may be as high as 1.5 million. A conference on abortion here in 1975 also estimated that illegal abortionists in Italy may earn as much as $100 million tax free each year.

There is no way to check these figures, but a young Naples gynecologist said in a recnt interview that he had earned over $1.2 million by performing some 14,000 abortions in two years.

The law was passed by a coalition of pro-abortion parties who outvoted the ruling Christian Democrats who normally are their partners in a parliamentary majority. The outcome, however, was not expected to have any effect on the stability of Premie Giulio Andreotti's government.

Earlier this week Andreotti received a massive vote of confidence from parliament on a new antiterrorism decree. Furthermore, the Christian Democrats and their allies agreed long ago to disagree on the abortion issue.

The new law, which replaces 1930 legislation making abortion a crime under all circumstances, will allow any woman over 18 to decide with or without a doctor's approval to have an abortion within the first 90 days of pregnancy if carrying the fetus to term could have negative effects on her "physical or psychic health."

Article four of the new bill makes it clear that economic, social and family conditions, as well as sexual attack or a malformed fetus, are considered valid factors that could endanger a woman's health.

Article Five spells out one of the major demands of Italian women's groups, that despite requirement consultation with a doctor and a legally prescribed seven-day period of reflection, the final decision to terminate a pregnancy "belongs exclusively to the woman."

The same article states that the father of the fetus will be consulted only if the woman agrees. In the case of pregnancies that have already gone beyond 90 days, abortion will be allowed only when there is serious danger to the woman's life or "significant malformations of the fetus.

Another controversial clause, Article 12, allows women under 18 to have abortions if their parents or guardians agree. Yet, the law continues, if there are "serious reasons" why consultation with the parents is impossible or inadvisable, a judge can make an irreversable decision on the basis of a doctor's report and the girls wishes.

The bill is nearly as liberal as abortion laws in the Scandinavian countries. It passed in the face of Pope Paul's condemnation of abortion as homicide.

In the United States, the Supreme Court has ruled that abortions on demand are legal when the mother is less than 24 weeks pregnant.

Laws in Britain and West Germany require a doctor's approval for abortion. In France women can make their own decisions up to the 10th week of pregnancy, and abortion is illegal in both Belgium and the Netherlands.

In another key clause, the bill gives regional health authorities the financial and practical responsibilities for all abortions. The operation will be paid for by the woman's national health plan.

The bill is the third abortion law introduced in the Italian parliament over the last two years. The first, in early 1976, sparked a bitter political controversy that brought down the government and forced early elections in June of that year. Pro-abortion parties returned with enough seats, on paper, to outvote the Christian Democrats and neo-Fascists who strongly opposed the bill. Last year, however, after initial passage of an almost identical bill in the Chamber of Deputies, the senate narrowly voted down the law in a surprise 156 to 154 vote.

Several senators crossed party lines to vote against that bill because it allowed abortion for 16-year-olds and it failed to mention any role for the father of the conceived child.