A 73-year-old Brazilian who heads an ultraconservative organization whose symbol is a heraldic lion has launched a million-dollar campaign against the new French government by publishing his attacks as paid advertisements in major newspapers in 15 countries.

At the going rate for the prime space purchased for the ads, the propaganda is expected to cost about $2 million, but the group's leader refused to say who is financing it.

Plinio Correa de Oliveira presides over the Society for Tradition, Family and Property, an all-male quasi-religious group with branches in 12 countries, including one in Pleasantville, N.Y., from a baronial -- but rented -- mansion in Sao Paulo's affluent suburb of Higienopolis. In recent weeks, his rambling broadside against socialism in France under President Francois Mitterrand has been published as six pages of paid advertising in the news sections of The Washington Post, The New York Times and several European dailies.

"Everyone is interested in knowing where the money is coming from, but no one asks where the money for Mitterrand's propaganda comes from," Correa said in an interview at his headquarters here, adding only that the money was raised "among friends."

The Dec. 9 publication in The Washington Post, at the base rate of about $19,000 per page plus surcharges for special placement, is estimated to have come to more than $114,000, although The Post's advertising department has refused to disclose the exact cost.

Correa said the affiliate in Pleasantville paid for that ad and one published simultaneously in a West German newspaper.

He said that other TFP chapters would publish the polemic in major newspapers in France, England, Canada, Italy, Spain, Portugal, Argentina, Bolivia, Brazil, Colombia, Chile, Ecuador, Uruguay and Venezuela.

The ad, illustrated with pictures of Roman Catholic popes and Communist leaders such as Leon Trotsky and Vladimir Lenin, charges that the French Socialist Party aims at the "disintegration" of society into an "anarchic utopia," and criticizes the Mitterrand government for advocating "free love" and women's equality.

The goal of the campaign, Correa said, is "to alert public opinion of the West as to the true content of the Socialist Party platform," which the advertisement describes as a "trainbearer" of international communism.

The danger of Mitterrand's "self-management" socialism goes back to the French Revolution, whose espousal of liberal and egalitarian ideas is at the root of many of the world's ills, according to Correa, who is described in TFP literature as a journalist and professor of history of civilization.

"The internal events of France are easily irradiated throughout the world," said Correa. "There hasn't been an important event in France that didn't have an ideological repercussion in the world at large."

As Correa talked, a young black servant appeared, dressed in a white linen tunic with gold epaulets and white gloves, carrying a silver tray of coffee cups. As the servant stood stiffly, Correa continued his political discourse for another five minutes without deflecting his gaze from his guest. Having concluded a point, he silently motioned to the attendant to serve coffee.

TFP members, about 1,000 in Brazil, proudly style themselves as "counterrevolutionaries." Although Correa is reticent about the sources of funding, the roster of the organization's national council includes Adolpho Lindenburg, the president of a large Sao Paulo construction company.

After Correa founded the organization in 1960, he drew heavily on the support of large, rural landowners. One of the TFP's first campaigns was a petition drive in the early 1960s that succeeded in blocking an agrarian reform bill.

In Chile, where the Roman Catholic Church has been a bulwark in defense of human rights in recent years, TFP has matched its support for the anticommunist dictatorship with publicity attacking the Catholic hierarchy as favoring "Marxization" of the country. After a round of clashes in 1976, Chile's Cardinal Raul Silva accused TFP of attempting to "create a regime of persecution against the church."

Other TFP targets include the human rights policy of former president Carter, pornography, rent control, Catholic masses in Portuguese and the theology of liberation, a Latin American intellectual movement wedding Catholic doctrine and revolutionary social action.

High above a protecting wall at Correa's Higienopolis headquarters flies a 20-foot medieval-style banner emblazoned with the society's shield: a golden lion rampant on a crimson field.

Young men with crewcuts guard the entrance and usher visitors into the great hall, lit by Venetian-style torches. On the walls hang 18th century engravings depicting two heroes of the organization: Louis XVI and Marie Antoinette.

Nearby, the Louis XVI room contains period furniture and walls covered with French silks. In the Brazilian colonial rooms, stands a crucifix with the wounds of Christ encrusted with rubies.

Correa is proud of his European lineage, and can trace his ancestry back to ministers of the last Brazilian emperor, Dom Pedro II. The pretender to the Brazilian throne, Prince Luis de Orleans e Braganca, lives in a TFP house.

Correa says he does not admit women because "they would just get in the way," during the organization's street proselytizing, which is sometimes done by militants wearing crimson sashes and carrying standards on poles topped with fleur-de-lis, the coat of arms of the former French royal family.