RIO DE JANEIRO, DEC. 31 -- A new proposal to ease Mexico's foreign debt with indirect U.S. backing is a good sign for No. 1 debtor Brazil, acting Finance Minister Mailson de Nobrega said yesterday.

"This {Mexican plan} is an extremely positive fact for Brazil," Nobrega told the daily financial newspaper Gazeta Mercantil.

On Tuesday, Mexico and the United States announced a plan in which the United States would sell bonds to Mexico, which in turn would issue its own bonds in exchange for a much larger amount of current debt.

Mexico is the developing world's second-largest debtor, owing foreigners $105.3 billion. Only Brazil owes more, $116 billion.

"Imaginative solutions are starting to appear," Nobrega said. "This is a demonstration that creditor countries are starting to accept the need for a lasting solution to foreign debts."

Nobrega indicated, however, that it was unlikely Brazil could get the same kind of arrangement. Mexico was able to do it because it has at least $2 billion in its cash reserves.

Nobrega said Brazil does not have sufficient reserves to make a similar bond issue.

Earlier in 1987, Brazil suggested that part of its debt be exchanged for long-term bonds, but creditor banks were cool to the idea.

Brazil at first proposed the exchange be compulsory, and at a significant discount, with the bonds guaranteed only by the Brazilian government. Mexico's bonds, in contrast, would carry the U.S. bonds as collateral.

Nobrega said that even if Mexico's bond program cannot be copied by Brazil, it should help Brazil negotiate some kind of debt-for-bonds deal when it meets bankers in two weeks in New York.

Brazil stopped paying interest Feb. 20 on some $70 billion of medium- and long-term private bank loans, but in December made a partial payment.