Splinter factions picked fistfights with each other. Raucous workers cheered or booed minor speakers. Finally, after two hours under the tropical sun, the impatient crowd began a low crooning:"luuuulaa, luuulaa."

The stocky man mounted the platform. The factional chants died away. Those sitting in the shade drew near.

Gripping a microphone in his left hand, the orator used his hammy right arm as a baton for a proletarian orchestra. Fiercely jabbing his forefinger skyward, the labor leader drew a crescendo of cheers and whistles as he rhythmically denounced Brazil's military government.

"We are tired of living in slums; we are tired of going hungry," he shouted.

Nicknamed "Lula," Luis Inacio da Silva is Brazil's -- and probably Latin America's -- most charismatic labor leader. Last week a military court convicted Lula of leading an illegal strike and sentenced him to 3 1/2 years in prison. He was found guilty with 10 other unionists, but after a day in jail, all were freed pending appeal.

At 36, Lula is president of Brazil's Workers Party. A new phenomenon among Brazil's traditionally elitist parties, the party enjoys wide support among the Roman Catholic Church's 100,000 activist lay groups. The generals ruling Brazil are known to view the rapidly expanding party as a threat in national elections scheduled next year -- the first serious electoral contest since the conservative military seized power here in 1964.

"Brazilian political parties have always been organized from the top down. We are organizing from the bottom up," Lula said in an interview last week.

But last week's guilty verdict throws Lula out of the race personally. Convicted felons cannot run for elected office.

Lula's crime was to lead an estimated 200,000 metal workers out on Brazil's longest major strike since 1964. With the massive Brazilian auto industry outside Sao Paulo shut down for six weeks, the military became so furious that they buzzed workers' rallies with machine gun-equipped helicopters and threw Lula in jail for 30 days.

Unions here negotiate new contracts each March and April and the timing of last week's trial is seen as a direct warning that the government's abertura , or democratic opening, is closed to labor.Through the three-year-old abertura policy, President Joao Baptista Figueiredo has lifted press censorship, emptied the jails of political prisoners and allowed exiles to return under an amnesty program.

"The abertura doesn't exist for the working class," Lula charged before going to jail Wednesday night.

The government stalled the trial until 48 hours before carnival -- apparently hoping the annual five-day pre-Lenten bacchanalia would soak up popular outrage.

"the judgment of the most important trial of Brazil's abertura was set for the eve of carnival," editorialized the liberal daily Folha de Sao Paulo. "Brazil will wake up Ash Wednesday free of the implications of the trial and having forgotten everything."

With domestic anger diverted, officials attempted to muffle international reaction by barring all foreign reporters from the courtroom. Nevertheless, protests have flowed in from unions in 10 European countries and from 25 U.S. congressmen, including Sen. Edward M. Kennedy [D-Mass].

"War is war," was the justification for barring foreign journalists, according to a public relations officer of the 2nd Army here.

On the other side of the barricades are Brazil's second-generation industrial workers, more militant than their fathers and less willing to accept wages one-sixth as high as U.S. and European rates. The ratio of lowest salaries to highest averages 1 to 100 here but can rise as high as 1 to 200.

Biographical sketches of Lula and his fellow defendants reveal two recurring factors -- all but one immigrated as a child to Sao Paulo from poorer areas of Brazil and all began working at a very early age.

Lula recalls his first view of Sao Paulo came at the end of a dusty, 13-day ride in the back of a truck. In 1951, a two-year drought forced his parents to abandon their sweet potato farm in the northeastern state of Pernambucco and try their luck in the rapidly industrializing south.

By age 11, Lula was working in a dry cleaners to help support his six brothers and sisters. His formal education stopped in the 8th grade. After an apprentice course, Lula became a lathe operator in a steel factory, later losing a finger in a machine press.

After his brother was arrested for union activism in the late 1960s, Lula entered union politics and rose swiftly to the presidency of the metal workers union. At the height of last year's strike, the government stripped him of this post and installed in his place a government appointee.

The Workers Party has never competed in an election so it is difficult to gauge Lula's popularity.

While Lula's charisma appeals to the man in the street, many of his party workers come from intellectual leftists factions and Lula admits he works hard to prevent the radicalization of his party.

The party manifesto makes a pitch to "all victims of capitalism." But the charter never mentions socialism, and, instead, hews to a militant trade unionist line.

Ironically, while Lula's personal prestige and popularity have never been higher, the number of strikes in Brazil has hit a low from the peaks of 1978 and 1979. According to the Labor Ministry, there were about 25 strikes last year, compared to 300 in 1979.

"I think the workers are getting a fairer deal now -- people are getting big salary increases," Ernest S. McCrary, editor of the English-language newsletter Labor Trends, said in an interview.

Under a new policy started last year, low-salaried workers receive automatic cost-of-living increases mandated by the government. They can then negotiate additional raises with employers. Brazil's military clamped down on all labor agitation from 1968 to 1977, and employers were caught off balance by the first waves of strikes, McCrary said.

"The companies are getting smarter. They are hiring labor relations people for the first time," he added.

But auto workers here start contract negotiations next week, and they have already demanded 25 percent raises over the cost of living. In what may prove an omen, 1,200 Ford employes stopped work last Thursday to protest Lula's conviction and sentence.