Top Brazilian financial officials today told bankers from a score of nations that the financially-troubled Latin American nation needs $9.6 billion in long-term funds to be solvent in 1983.

At a meeting at the Plaza Hotel here, Brazil's Central Bank President Carlos Geraldo Langoni asked representatives of 125 banks to give $4.4 billion in new long-term loans, hold to commitments they made last year to loan another $1.2 billion and refinance $4 billion in repayments that are due to be made in 1983.

In addition the Brazilian officials asked the banks to make sure there is no reduction in the $8.8 billion that Brazil must borrow for short periods of time to finance its foreign trade or the $10 billion line of foreign credit that Brazilian banks use to balance overnight international accounts.

Langoni said telexes will go out to all banks with loans to Brazil by Tuesday or Wednesday, asking them to cable their acceptance "in principle" by Dec. 31. The 125 banks assembled today hold about 90 percent of the $59 billion Brazil owes foreign commercial banks. All told, Brazil owes $80.2 billion to banks and other entities such as governments and international lending institutions.

"As far as I'm concerned, when you add the whole thing together including the trade and interbank financing credits it's almost a $30 billion refinancing," said a senior official at a major U.S. bank.

Langoni, at a briefing tried to paint a brighter picture, stressing that his nation is asking its bankers to increase their "exposure" to Brazil by only $4.4 billion -- the amount of new loans the government is requesting.

International Monetary Fund Director Jacques de Larosiere also addressed the bankers at the two-hour seesion, urging them to comply with Brazil's request.

Noting a standard condition for IMF loans, he warned that if most of them did not go along with the proposals, the $4.86 billion the IMF has tentatively agreed to lend Brazil over the next three years would not be forthcoming either.

"It was a 'we hang together or we hang separately' speech," said a U.S. banker who attended the session.

Brazil, as part of the IMF pact, has agreed to take severe steps to hold down its borrowing needs. It has agreed to further devaluations in the cruzeiro to make Brazilian exports more competitive and imports less attractive. It also has agreed to phase out subsidies to farmers and to sharply reduce its spending on investment projects to reduce the government's budget deficit.

Langoni said Brazil's problems are due to a combination of factors including high interest rates and falling commodity prices, but he said that were it not for the Mexican debt crisis, which made banks wary of lending to any Latin American country, the current problems would have been less severe. Brazil had to draw on $4 billion of its foreign currency reserves to meet debt payments in October and November.

Bankers said after the meeting that the Brazilian presentation was "very professional" and that they felt most banks would go along with the package. However, the Bank of Boston's vice president in Brazil, Joah Devine, warned prior to the meeting that the confidence of the smaller regional banks upon which Brazil's borrowing plans depend "will not come back overnight."

The quick response to Brazil's plight is the work of a loosely knit international safety net arranged by governments, international lending institutions like the IMF and private banks -- an arrangement that is being tested by the debt crises confronting Brazil and a half-dozen other nations.

* The response began with large U.S. banks -- who faced the greatest immediate loss if Brazil defaulted. They pledged $600 million in new, temporary loans. The banks--Bank of America, Citibank, Chase Manhattan, Manufacturers Hanover, Chemical and Morgan Guaranty Trust -- assumed that this additional loan would soon be repaid by the IMF -- providing Brazil and the IMF could agree on a new loan program.

* The U.S. government agreed to a $1.23 billion loan, which was nearly all drawn by the time President Reagan announced it last month during his trip to Brazil.

* Then, over the weekend, the Reagan administration, joined by the central banks of the other major industrial countries, approved $1.2 billion more in loans, with an additional $600 million from the United States.

* This package of emergency funds is to be repaid from a $4.86 billion three-year standby loan from the IMF, under an agreement reached in Brazil, with the IMF insisting on additional austerity measures by Brazil's leaders.