Ireland's voters appeared today to be giving overwhelming approval to a proposed constitutional amendment that would prohibit abortion. Early reports indicated that the amendment would pass, in expected light voting, by a margin of about 2 to 1.

The vote on the referendum climaxed one of the ugliest and most divisive campaigns in recent Irish history. Analysts predicted that because of widespread confusion over the issue and disgust over the tactics of the rival sides, more than 1 million of Ireland's 2.3 million eligible voters would not go to the polls.

Abortion has been illegal in Ireland for 122 years, and there is no widespread support for liberalization of the 1861 anti-abortion statute. Nevertheless, anti-abortion groups have been lobbying for several years for a constitutional ban so abortion cannot be legalized here by court decision, as it was in the United States.

Both sides in the debate over the amendment agree that, pass or fail, the measure will do nothing to stop an estimated 7,500 Irish women from going to Britain for legal abortions each year.

That is about the only thing they do agree on. Motorists who inched their way through the crowded city center this morning were greeted by big white banners with the rival campaign slogans: "Vote Yes for Life" and "Irish Nation or Catholic State?" Epithets like "baby killers" and "papal puppets" have peppered the referendum campaign.

"What we have as a result of this referendum is another Irish civil war," said a former member of the Irish Parliament, Jim Kemmy, an opponent of the referendum.

Irish nationalists who favor a united Ireland say that the sectarian nature of the proposed amendment will set back moves to bring predominantly Protestant Northern Ireland into the republic.

Within the republic, the acrimonious abortion amendment debate has been raging for almost a year, dividing the country along both religious and political lines. The pro-amendment groups have the backing of the powerful hierarchy of the Roman Catholic Church (which claims membership of 95 percent of the population), a well-organized group called the Society for the Protection of the Unborn Child, the League of Decency, the Knights of Columbus, the Irish Nurses Association and many prominent public figures, including Nobel Prize winner Sean MacBride.

On the anti-amendment side are the leaders of all the Protestant denominations, Prime Minister Garret FitzGerald (a Catholic) and 60 small groups representing everything from Catholic Farmers Against the Amendment to the Anti-Amendment Musicians Organization.

A "pro-life" amendment was introduced in Parliament on the day the last Fianna Fail government collapsed last fall. During the subsequent election campaign, both Fianna Fail's leader, then-prime minister Charles J. Haughey, and Fine Gael's FitzGerald promised to hold a referendum on the proposed amendment within months of assuming office. After Fine Gael's victory, FitzGerald balked at holding the vote, saying that his attorney general had warned him that the ambiguous wording of the amendment, which guarantees the "unborn" a right to life equal to the mother's, would create havoc in the Irish courts and medical community.

Opponents of the amendment say it is open to many interpretations. They charge that accepted medical practices such as surgery during ectopic pregnancies might be rendered illegal should it become law, and one of their slogans has been, "This Amendment Could Kill Women." Opponents also say that the amendment might ban some methods of contraception. It was only four years ago that contraception was legalized in any circumstances, and contraceptive devices still are legally available only to married couples.

Supporters of the amendment accuse their opponents of scare tactics. They say that if the amendment becomes law it will do no more than guarantee that abortion will never slip through Ireland's back door.

During the past week large numbers of angry Catholics have walked out of Sunday masses, a national television debate was delayed because of bomb scares, and amendment supporters accused anti-amendment people of stealing a statue of the Virgin Mary from a shrine along a main street here. Spokesmen for both camps said yesterday they would be relieved to see the campaign end.

In a final contribution to the divisions and confusions, the country's bus and railroad workers today announced a one-day strike, leaving commuters stranded and many voters without transportation to the polls.