The new divorce law is a labyrinthine document that appears to raise as many obstacles as it removes. The product of much bickering and compromise in the congress, it permits Brazilians to "petition for divorce" just once - and then only after a three-year separation.

Proponents of a more liberal divorce measure argue that under the current law, an improperly worded divorce petition would be enough to disqualify a couple from taking any further action - and that any couple including one partner with a previous divorce could not set a divorce.

Despite the restrictions aimed at reventing Brazilians from approaching divorce too lightly, the new law continues to be criticized by the Roman Catholic church, leader of the forces that had opposed its passage. Any divorce law, says Cardinal Vincente Scherer of Porto Alegre, "signifies the renuniciation and abandonment of one of the most fundamental values of human society."

Days after the bill was signed into law, a church spokesman announced that the church would no longer accord equal status to civil ceremonies and added that all couples planning a church wedding would henceforth be required to sign a pledge acknowledging the "indissolubility of marriage."

Later, though, another member of the church hierarchy said that official action on this and other divorce-related questions would be reserved until April, when the National Conference of Brazilian Bishops is to meet.

Throughout the long, bitter struggle, Brazil's all-powerful military rulers have remained neutral. Gen. Geisel, the nation's first Protestant president, promised early to abide by whatever decision the congress reached, preferring the uncertainties of the legilsative process to the alternative some opposition-party divorce advocates were proposing: an Italian-style national referendum.

Geisel inadvertently gave the bill a boost, however, when he temporarily closed the congress and decreed faraching institutional reforms last April. Among the measures included in the harsh "April package" aimed at circumventing growing opposition electoral strength was one reducing the majority needed to pass a constitutional amendement from two-thirds to one-half.

When that decree went into effect, opposition Sen. Nelson Carneiro of Rio, who had unsuccessfully introduced six divorce bills since 1951, decided to try again. A much-amended version of the Carneiro bill was finally approved in December, with a majority that cut across party and ideological lines.

With a steady stream of divorce petitions now flowing into the courts, the new law is providing fodder for gossip columnists and mass circulation magazines. Brazilian literazy figures and move, television and pop stars, who change partners with the same regularity as their American counterparts, are already involved in several widely publicized proceedings.

To the public's surprise, though, the most active seekers of divorce thus far seem to be the elderly, who are often motivated by a desire to regularize de facto marriages of long standing. One of the first divorcees was a 75-year-old businessman separated from his wife for over 25 years and with two "illegitimate" teen-age children from his second union.

One other group has responded to the advent of divorce with notable enthusiasm: lawyers. In addition to their activities in court, attorneys are now writing books and essays interpreting the measure, placing discreet newspaper ads offering their services and trying to draw up a standardized fee schedule for divorce cases.

The fee scales are expensive by Brazilian standards, amounting to much as a year's salary for someone earning the minimum wage. So, to put the new law within the reach of the lower-class customers, some lawyers in poor areas have begun offering divorce on the installment plan.