Italians today appeared to have overwhelmingly defeated a church-backed proposal to overturn the country's liberal abortion law in a referendum vote, despite predictions that sympathy for Pope John Paul II, recovering from last Wednesday's assassination attempt, would sweep the antiabortion move to victory.

On May 10, only three days before he was shot, the pontiff in St. Peter's Square that "the church condemns any legislation favorable to procured abortion as a very grave offense against man's basic rights and the divine commandment, 'Thou shall not kill.'"

In preceding weeks the pope had spoken out on several occasions against abortion, which the referendum proposal, backed by both the church and the ruling Christian Democractic Party sough to limit to women whose lives were threatened by carrying their pregnancies to term.

Public opinion polls published earlier this month indicated that the effort to change the law was likely to carry by a margin of about two or three percentage points.

Instead, early returns, with 27 percent of the votes counted, gave a nearly 70 percent margin to those favoring the present law, which allows women over 18 to have abortions on demand within the first 90 days of pregnancy at the state's expense.

In four other votes, Italians in even larger majorities opposed proposals sponsored by the small Radical Party to repeal a tough antiterrorism measure permitting detention without charge for up to 48 hours, end life imprisonment and prohibit gun licenses for people who are not policemen.

Also, resoundingly defeated was a separate, Radical-sponsored proposal to liberalize the current abortion law. The Radicals, who originally spear-headed the abortion movement here, back changes that would allow women under 18 to have abortions without restrictions and permit private doctors to perform abortions in outpatient clinics.

With more than half of the vote countd on the four Radical proposals, the results were 85.4 percent to keep the antiterrorism measures, 86.7 percent on gun licensing, 76.9 percent to keep life imprisonment and 88.8 against the proposal to further liberalize the abortion law.

The results of the balloting indicated for the second time in seven years that Italian voters are no longer strongly influenced by the church on civil rights or social issues. In 1974, a church-sponsored antidivorce referendum was defeated by 60 percent of the voters.

On the abortion issue, the referendum also represented a clear setback for the ruling Christian Democrats. More significantl, the results of the balloting represented a decisive defeat for the Radicals, a group that began a decade ago as a civil-rights, single-issue movement and by the last general elections in 1979 had won enough support to increase its seats in parliament from four to 18.

The election also seemed bound to raise further questions about the increasing use of Italy's referendum mechanism. This weekend's vote was the fourth time since World War II that referendums have been held here. The first was in 1946, and the last three have been since 1974.

Although the first referendum in recent times, that against divorce in 1974, was sponsored by the church, the mechanism soon became a favorite of the Radicals, who believe that an instrument of direct democracy is necessary in a country dominated by a parliament that, once in office, maintains little contact with the electorate.

Many "establishment" politicians believe that by pushing for frequent referendums the Radicals have twisted the sense of the constitution. Although no action has yet been taken, there has been pressure to change the number of signatures needed to sponsor a referendum from 500,000 to 1 million.