BUENOS AIRES, Argentina (AP) _ The House of Deputies began debating a bill Wednesday to legalize divorce despite strident opposition from the Roman Catholic Church.

It was the first time a divorce bill had reached the floor of a congressional chamber in three decades in this heavily Catholic country.

About 90 percent of Argentina's 28 million people are Catholics, but only about one in 10 say they are active churchgoers.

The proposal has the support of most of the 254 deputies, and if approved as expected this week it would go to the Senate, where its fate remains uncertain because the 46 senators are more evenly divided on the issue.

In the House, Nestor Perl of the Peronist Party called it ''a bold act in the face of those who want to leave things as they are, believing that the law can keep united those who through lack of affection are already separated.''

Perl said, ''We must defend the family against those that divide it into first-class and second-class families, as happens today with the placement of the concubine in the inferior category.''

While Argentine law prohibits divorce, tens of thousands of married couples live apart, often with new partners who have no legal rights. Children of such relationships by law do not have the same inheritance rights as those from marriage.

Public opinion polls have indicated about seven out of 10 Argentines favor legalizing divorce.

But an opponent, Carlos Auyero of the Christian Democratic Party, said its passage would result in ''trauma'' to the family.

''It is not the state which creates the bond between man and woman, nor even a priest, and thus it cannot be dissolved by them,'' Auyero said. The marriage vow ''is assumed by the couple in perpetuity,'' he said.

The church has come out strongly against the bill, and in July organized a series of rallies to demonstrate popular opposition. The largest rally, in Buenos Aires' central Plaza de Mayo, attracted 50,000 people but many other rallies were poorly attended.

Monsignor Emilio Ognenovich, head of the national episcopate's family secretariat, said Wednesday that the Congress ''is demolishing the indisolvability of matrimony, to the sorrow of many Argentines.''

Ognenovich did not attend the debate, saying ''it would be inopportune, and interference... in the legislative activity.''

He said the congressional debate was taking place during ''a general apathy'' regarding the divorce issue. ''The Argentine family faces many urgent, more important needs that require their attention, such as the insufficiency of salaries,'' he said.

The church says lawmakers should drop the divorce issue for what it feels are more pressing issues, such as the country's economic crisis.

Supporters hope to get the bill to the Senate before the end of the congressional session on Sept. 30. If not, Senate treatment may wait until next year, after a scheduled April visit by Pope John Paul II, who opposes divorce and is widely respected in Argentina.

A divorce bill has not been debated by Congress since 1954, when then- president Juan Peron pushed through a law during a bitter feud with the church. That feud, which included the sacking of some churches by Peronists, was in part responsible for the military overthrow of Peron in 1955. The country's new leaders quickly struck down the divorce law.

It was the only time in the country's 186-year history that divorce was legal.