Thousands of faithful waited in the cold rain for a glimpse of Benedict, then chanted "Bento, Bento" and waved flags of different South American nations as he blessed them at the monastery where he is staying.
The Vatican says Benedict will confront major challenges during his visit, such as the church's declining influence in Brazil, the rise of evangelism, and efforts to expand access to abortions in the region.
Catholic officials have been debating for some time whether politicians who approve abortion legislation as well as doctors and nurses who take part in the procedure subject themselves to automatic excommunication under church law.
The pope was asked where he stands on the issue during the flight to Brazil, in his first full-fledged news conference since becoming pontiff in 2005.
"Do you agree with the excommunications given to legislators in Mexico City on the question?" a reporter asked.
"Yes," Benedict replied. "The excommunication was not something arbitrary. It is part of the (canon law) code. It is based simply on the principle that the killing of an innocent human child is incompatible with going in Communion with the body of Christ. Thus, they (the bishops) didn't do anything new or anything surprising. Or arbitrary."
Church officials later said the pope might have inferred from the question that the Mexican bishops had issued a formal declaration of excommunication for the legislators, something Mexican Cardinal Norberto Rivera has said he has no intention of doing.
Benedict's spokesman, the Rev. Federico Lombardi, said the pope was not setting a new policy and did not intend to formally excommunicate anyone -- a rare process that is separate from the doctrine of self-excommunication.
"Since excommunication hasn't been declared by the Mexican bishops, the pope has no intention himself of declaring it," Lombardi said in a statement approved by the pope.
