''May 1988 could be a turning point,'' said Jacques d'Adesky, an economics professor of mixed ancestry who specializes in development. ''This is a moment of consciousness-raising. I think it will leave a deep mark.''

About 600 black groups have sprung up in the more liberal political climate of the last several years as Brazil has moved from military to civilian rule. With a variety of focuses, both political or cultural, they have widely varying strategies for change. In the Atlantic port city of Salvador, sometimes called the capital of black Brazil, where only 20 percent are white, many blacks have adopted the style and pan-African ideology of Jamaica's Rastafarians.

In the months leading up to the centenary, there also was a surge of complaints about discrimination and abuse, a reflection, perhaps, of a greater willingness on the part of victims to speak out. At S O S Racism, a private civil-rights organization that investigates and publicizes cases of discrimination in Rio de Janeiro, Wilson Prudente, a sociologist, said many callers complain of police mistreatment, employers who pay black workers less than whites, or private schools that exclude black students. Social Injustice

One caller said that an elegant sports club regularly barred black nursemaids accompanying white children if they did not wear a ''nanny's uniform.'' Another told of a police patrol on a bus, making routine identity checks, that approached only the five black passengers.

In a notorious case reported by newspapers in March, a white doorman ''punished'' a black maid, Vera da Silva, in an apartment building when she entered the main elevator instead of the service elevator. The angry doorman decided to teach the ''insolent black'' a lesson and trapped her inside the elevator for half an hour.

These were small scenes, perhaps, on the ample roster of Brazilian social and racial injustices. What made them unusual is that the victims protested. Much of racism here, blacks say, cannot be confronted because it comes in ways that are hard to prove or fight. Although racial discrimination has been against the law since 1951, a subtle social code is still prevalent in Brazil. Job advertisements, for example, seek individuals of ''good appearance,'' a euphemism for light skin. Less Tangible Than in U.S. ''How do you prove it was your color?'' asked Rosenir Muniz, a historian and computer programmer. She said she had given up after 20 months of making telephone appointments for job interviews because the jobs would suddenly be filled when she showed up.

American blacks who live or visit here say that racism is less harsh and less tangible than in the United States, more hidden beneath the conviviality of Brazilian life. From the early days, white Portuguese colonists had children with black concubines. ''The Pilgrim Fathers brought the Pilgrim mothers, but the Portuguese at first came alone,'' a Brazilian historian said.