Ignoring U.S. moves to tighten the trade embargo against Cuba, Brazilian businessmen are taking steps to restore trade between the Caribbean island and Latin America's industrial giant.

In the first major mission by Brazilian businessmen to Cuba since relations were suspended in 1964, Ruy Barreto, president of the powerful Confederation of Trade Associations, led a five-man group to Havana late last month. Five days of discussions with top Cuban ministers followed, and were capped by a four-hour meeting with President Fidel Castro, who offered Brazil "preferential trade status."

"If we don't have the United States, countries like Brazil, Mexico and Argentina offer great possibilities for trade," Castro told a Brazilian reporter who accompanied the trip.

Returning to Rio, Barreto estimated that Brazilian exports to Cuba easily could reach $200 million annually, and he predicted rapid growth in triangular trade. In 1980, Brazil's total exports were $20.1 billion, its imports $23 billion.

From Brasilia, President Joao Baptista Figueiredo issued a note declaring that Barreto's trip was a private undertaking without government backing, and that official policy toward Cuba remains unchanged: diplomatic and economic ties remain suspended.

But unofficial reaction to Barreto's trip was generally favorable. The press gave extensive, and sympathetic, coverage, and a series of prominent business figures publicly praised "the opening to Cuba."

"We need to export, even if it is to a communist country like Cuba," said Luis Lacerda Biagi, a Sao Paulo manufacturer who wants to sell sugar and alcohol production equipment to Cuba. "After all, we already deal with the Soviet Union, Poland, China, and practically all the socialist bloc countries," said Biagi.

Last year, Biagi received two delegations of Cubans interested in buying distillery equipment. Much of Cuba's sugar refining equipment is outdated, and Biagi said the Cubans are interested in Brazil's alcohol program where cars run on home-grown sugar cane alcohol fuel instead of on imported oil.

In separate statements, the heads of Brazil's shipbuilding and auto manufacturing associations praised the trip as a move to open a new market.

"I am sure we could offer Cuba virtually everything," said Barreto. "Brazil has already attained a level of industrialization capable of attending the needs of a country like Cuba," he said.

The Brazilian group did not negotiate specific sales, but Barreto said he was surprised by the number of Brazilian products already in use in Cuba.

Brazil recently made exports a top priority, with the goal of selling enough abroad to pay for imported oil. Brazil imports 75 percent of the oil it consumes.

In Brasilia, two floors of the seven-story Ministry of Foreign Relations are occupied by the Department of Trade Promotion. In Africa, Brazilian diplomats frequently criticize South Africa's system of racial separation as "a crime against humanity," but during the first 10 months of 1981, Brazil exported $116.3 million worth of goods to South Africa.

Brazilian recognition of the Castro government seems unlikely for the moment, and some trade analysts say this will stunt any unofficial third-party trade.

Last year, Argentina, Cuba's largest Latin American trading partner, exported about $300 million worth of products to Cuba. In return, the Argentines received mostly sugar, tobacco, and citrus fruits--all products currently exported by Brazil.

The fact that Cuba seems to have little to sell that Brazil does not have already may create a problem for developing trade. Without Cuban commodities to trade for Brazilian goods and without access to government-subsidized credit, Brazilian manufacturers will have to turn to private banks to finance major exports. Brazilian bankers, however, are wary of lending to communist countries short of hard currency. Brazil is now rescheduling a $1.5 billion debt owed by Poland.

Nevertheless, Barreto, a successful capitalist who owns 23 companies, believes that commerce with communist countries can be profitable. Two years ago, he won the exclusive franchise to sell his brand of coffee at the Moscow Olympics. Later this year, he is to lead a trade delegation to China.

Two weeks ago, Barreto, a graduate of Brazil's senior war college, celebrated his 55th birthday at a party given at the Cuban Chamber of Commerce. The host was Fidel Castro.