Brazilian opposition leader Leonel Brizola returned Friday from 15 years in exile, hailing the government-proclaimed amnesty that will enable him and thousands of others to participate again in public life as marking "the dawn of a new era."

Borther-in-law of deposed former president Joao Goulart and leader of the banned Brazilian Labor Party, Brizola was a popular state governor and federal deputy until force into exile in 1964. Since then, Brazil's military rulers have made him a symbol of -- and scapegoat for -- all the perceived evils of the period leading up to the 1964 coup.

His return was made possible only late last month, when the president, Gen. Joao Figuieredo, signed into law an amnesty for political opponents as part of his announced plan for a "slow and gradual" return to democracy for Brazil's 120 million people. Until then, Brizola faced 60 years in prison terms for illegal political activities.

Other prominent leaders of the pre-1964 era have indicated they will soon follow suit. Socialist Miguel Arraes already had announced that he will return from exile in Algeria Sept. 16, and Francisco Juliao, leader of the outlawed Peasant Leagues, in the impoverished Northeast, is expected to arrive from Mexico later this month.

Luis Carlos Prestes, 81-year-old chief of the Brazilian Communist Party, has been issued a passport in Moscow and is expected to return soon from exile there, perhaps by the end of this month.

Also among those receiving amnesties was Fernando Gabeira, leader of the group that 10 years ago this month kidnaped U.S. ambassador C. Burke Elbrick and held him in exchange for 15 political prisoners. Captured and alledgedly tortured by police, Gabeira was freed and flown into exile a year later, when the West German ambassador was kidnaped.

Brizola's reputation as a populist firebrand and his arrival on the eve of Brazil's independence day have meant that most of the public attention surrounding the government move has focused on him. Other beneficiaries of the amnesty measure are the more than 4,500 soldiers, civil servants, professors and public officials whose only crime was to have held political opinions offensive to the military government that took control.

The influx of exiles and the resurfacing of domestic foes has been greeted with words of skepticism and caution by the militgary elite. Army Minister Walter Pires de Albuquerque warned in a speech last week that "no one is going to set this country ablaze, I can guarantee you."

As presently formulated, the amnesty specifically excludes about 195 prisoners still held in jails for "terrorist" activities and "blood crimes." But the Air Force minister, Gen. Del. Jardim de Mattos, said earlier this week that the Figueiredo government is considering a plan to commute the terms of these prisoners.

The return of Brazola, 57, coincided with the publication in the press here of declassified CIA documents reporting that in the mid-1950s he organized a guerilla movement that was to be trained and financed by Cuba. Brizola has admitted contacts with Cuban leader Fidel Castro, but he says the charges have been exaggerated. He has promised a full explanation.

As governor of the state of Rio Grade do Sul during the early 1960s, Brizola was the most outspoken Brazilian critic of the United States. His nationalization of an ITT-owned utility company in 1962 marked the beginning of a period of uneasy U.S. relations that lasted until the military overthrew Goulart and seized power.

But after 13 years of exile in Uruguay and two years in New York, Brizola's fiery anti-American rhetoric seems to have cooled. Today he is a confessed admirer of President Carter's human rights policy and has aligned himself with moderate European socialists and social democrats such as Portugal's Mario Soares and West Germany's Willy Brandt.

The next step in the government's policy of political liberalization is reported to be due later this year with opening of the existing two-party system, created by decree in 1966, to pave the way for the legal reestablishment of Brizola's and other traditional parties.