Brasilia — Even as Brazil prepares to choose a civilian president, the nation's opposition politicians and its generals are disputing the prospects of another military coup.
Concern that the armed forces might block the scheduled return to civilian rule early next year appears to be related to the public-opinion lead that the opposition candidate has over the military government's choice for the presidency.
Although the current military president, Gen. Joao Baptista de Oliveira Figueiredo, vehemently denies any possibility of a coup, opposition leaders are alarmed by the Army and Air Force ministers' recent attacks on opposition candidate Tancredo Neves and those who support him.
Air Force Minister Brig. Delio Jardim de Mattos has charged that opportunists are trying to sell the Brazilian people down the river of leftist agitation.
''History does not speak well of cowards, much less of traitors,'' he said early this month, referring to some 60 politicians who have swung over from General Figueiredo's Social Democratic Party to support Mr. Neves and the demand for a direct popular presidential vote.
Army Minister Walter Pires also criticized defectors and warned against ''radical, sterile minorities who only want to sow disorder and chaos.''
The leader of the main opposition party, Ulysses Guimaraes of the Brazilian Democratic Movement, countercharged that such remarks only add to the nation's political confusion. Only in Brazil, he asserted, would changing one's party allegiance be seen as treason. The former governor of the state of Bahia, Antonio Carlos Magalhaes, says the armed forces should concern itself with security - and not, he said, act as a praetorian guard to a presidential candidate.
The parliamentary leader of the Democratic Labor Party, Brandao Monteiro, calls the Air Force minister's remarks ''an attempted coup.''
Neves could win both a direct popular election and an election by the currently scheduled method, an Electoral College vote, according to a recent opinion poll by the private Brazilian Institute of Public Opinion and Statistics.
The opposition candidate is not unpopular with the military. But many of them reportedly worry that he would be unable to control the extreme left - including the banned communist parties and MR8, an urban guerrilla group. These parties and the MR8 are all members of the opposition political coalition called the Brazilian Democratic Movement.
This fear lies at the root of the recent military warnings, say several analysts here. Some opposition members wonder whether, if such fear persists, conservative sectors of the military hierarchy might come to think the time is not yet ripe to completely relinquish power. Navy Minister Alfredo Karam is known to think that politicians are too indecisive. And this, he says, ''would eventually demoralize the public.''
The military has been in power since it staged a coup in 1964. Figueiredo, the fifth military president in these 20 years, is due to hand power to a civilian successor in March 1985. He has pledged five times recently that he would not tolerate any attempt at a coup, according to Democratic Labor State Deputy Alcides Fonseca, and has said he would rather die in office than permit a coup.
Admiral Karam, in an interview a week ago also sought to allay opposition fears about a coup.
''If something unfortunate occurred tomorrow and the President could no longer govern, the vice-president (Antonio Aureliano Chaves) would calmly assume power,'' he said.
Parliament remains bitterly divided between the opposition and defectors from the Social Democratic Party - who want the next president to be chosen by direct vote - and the government party, which supports the present indirect system of choosing the next president by the Electoral College.
The opposition's latest hopes were dashed last week when the head of Parliament, Sen. Moacyr Dalla, ruled that a constitutional amendment proposing the abolition of the Electoral College and allowing direct elections could be voted on immediately only if the leaders of all five political parties agreed. The Social Democrats are not likely to agree.
This will mean a straight fight in the Electoral College between Neves and government candidate Paulo Maluf.