Undaunted by severe new restrictions on their access to political power, leaders of Brazil's lone legal opposition party say they will continue to fight for a return to democracy here and in the rest of Latin America.

The opposition Brazilian Democratic Movement (MDB) has apparently decided that even under the dictatorial military government here, which has in effect become a one-party regime, a little democracy is better than none at all. Party leaders say that if they refuse to quit - unless physically forced - they still may be able to stem the tide of totalitarianism that is engulfing much of Latin American.

"We can still use our positions as congressmen to do some consciousness rasinig in favor of democracy," Sen. Andrt Franco Montoro, the minority leader in the Brazilian Senate, said in an interview. "We're better off than civilian politicians in countries like Argentina, Chile and Uruguay, where military governments have closed Congress indefinitely".

The head of Brazil's 13-year-old military regime, President Ernesto Geisel, a former army general, closed Congress earlier this month. He reopened it within two weeks, but only after dictating sweeping changes in basic election laws, which practically guarantee that the government party, National Renewal Alliance (ARENA), will come out best in all future national elections.

Geisel says he is trying to create "a better democracy" that "corresponds to Brazilian life."

The new rules, according to Rep. Alencar Furtado, the minority leader in the house, "beat and raped the MDB."

"I don't know how they continue under conditions like this," a secretary to an MDB congressman said. "If it were me, I'd resign and tell the president I wouldn't come back until Congress is really independent. How can a politician keep his dignity in such a situation?"

The president of the MDB, Rep. Uly-ssess Guimaraes, has an answer.

"Despite the precarious situation we are in, it is still worth it to continue fighting for democracy," he said. "The reason is simple: Democracy is the best form of government for Brazil. History proves it. The most advanced countries in the world today are democracies - with congress or parliaments.

The opposition must be very careful, however.

If opposition politicians speak out too stridently, they run the risk of being summarily fired by Geisel, who can remove any elected or appointed official in Brazil whenever he wants. This already has happened to several MDB congressmen who criticized the government.

Violent resistance is out of the question. Civilian politicians here still have vivid memories of leftist guerrilla groups that tried to set up power bases in Brazil in the late 1960s and early 1970s and were ruthlessly wiped out.

Sen. Franco Montoro believes the MDB should take full advantage of the elected offices it already has won under the limited democracy allowed by the military, to preach its message of the need for a return to full democratic rule.

"There are 9,600 MDB mayors and city councilmen in Brazil," he said. "We have hundreds more state representatives and federal congressmen. These elected offices are in effect 'battle stations,' and we should not abandon them."

Other MDB members, however believe it is a waste of time to work within what they see as an increasingly meaningless democratic facade. Rep. Joao Cunha, for example, believes the MDB should concentrate on increasing its contracts with people - "in universities, in people's homes, factory gates, on farmworkers' trucks and even in corner bars."

The MDB also is trying to get time on national radio and television, in accordance with an existing electoral law that allows the two parties to present their overall platforms to the nation. There are fears that the government will change this law too, if necessary, to keep the opposition party off the mass media.

The opposition also plans to attempt some low-key "consciousness raising" within the armed forces.

"There's a 'democratic wing' with in the military that's bigger than you think," Sen. Franco Montoro declared, but he did not elaborate.