A Declaration of Intent, a first step in the contract process, was signed this week by officials of both countries in Brasilia following a meeting between Russian Prime Minister Dmitri Medvedev and Brazilian President Dilma Rousseff.
The value of the proposed purchase is in negotiation.
"Everything will depend on the components of the systems that will be acquired," said Gen. Jose Carlos De Nardi, the head of the Joint Staff of the armed forces. "It is possible, for example, that the trucks (for the systems are provided by companies in Brazil. This would reduce the price.
"The details will now begin to be defined."
Brazilian officials said the air defense systems would be a mix of medium-range Pantsir-S1 systems and close-range Igla anti-aircraft weapons.
Talks on the procurement apparently began last December during a visit to Russia by President Rousseff and Defense Minister Celso Amorim.