Lelia Gonzalez concedes that her campaign this year for the Brazilian federal congress, organized and launched from the study table of her cluttered apartment, might be somewhat quixotic.

But Gonzalez, a 45-year-old anthropology professor, argues that the very fact that she is a candidate for congress in Brazil is a near revolutionary achievement. In a country whose military-ruled government is dominated by white males, Gonzalez is running not only as an outspoken feminist but also as a black and is seeking support from homosexual rights advocates.

"A barrier has been broken," she said recently. "A few years ago, no one would have believed that a candidate like me could exist."

With the broadest and most open Brazilian elections in 18 years of authoritarian rule scheduled for November, Gonzalez's compaign is only one indication of how Brazil's long disadvantaged minorities, including women, blacks, Indians and homosexuals, are beginning to take an active role in politics for the first time in the country's history.

Although activists in these social movements say their influence still lags well behind that of similar groups in the United States and Western Europe, not all of this year's candidates and groups face odds as difficult as Gonzalez. Broad political fronts have formed for both feminist and black candidates in the congressional and state government elections, and several major political parties have adopted feminist and black issues in their platforms. According to 1980 census statistics, 44 percent of the Brazilian population is black, Indian or racially mixed.

The government of President Joao Figueiredo, which is facing a stiff challenge from the opposition, has meanwhile begun responding to the political pressure of the new groups.

Government officials added a provision to the law of political parties last year requiring each party to have a women's commission, and more women and blacks have appeared on the tickets of the government's Social Democratic Party.

As the campaign heated up this month, Figueiredo also named Brazil's first woman Cabinet member, an education specialist who quickly announced that she was a feminist.

Perhaps the most dramatic development is the emergence of black rights activists in a country that 10 years ago prided itself as being a "racial democracy" where discrimination against blacks simply did not exist.

"There is more discrimination against blacks in Brazil than there is against blacks in the United States," said Carlos Alberto Medeiros, a black journalist and founder of the Brazil-Africa Exchange Society. "But 15 years ago no one acknowledged that it was a problem."

Now, black activists can point to extensive studies and statistics to persuade those who doubt charges of unequal status.

The growth of the social movements is directly linked by their leaders to the gradual expansion of political freedoms under the Brazilian military.

It is only this year that black and feminist candidates have actively worked to move into the political parties and support their own platforms and candidates.

The movements have met with substantial resistance within Brazil's traditional political ranks. At the first opposition party gathering attended by Rio de Janeiro's feminist groups this year, for example, their banner, reading "Our bodies belong to us," was altered by male party leaders to read, "Our bodies belong to you."

Both black and women's leaders have also faced resistance from more conservative black and women's leaders and from many Brazilian leftists, who argue that their issues should not be separated from the larger theme of inequality among Brazil's rich and poor classes.