RIO DE JANEIRO - Edward Snowden, the former contractor for the National Security Agency now living temporarily in Russia, said in comments published Tuesday that he is prepared to assist Brazilian investigations of U.S. spying in Brazil. But he said he cannot speak freely until a country grants him permanent political asylum, which he requested from Brazil earlier this year.

Snowden, whose disclosures of agency surveillance practices have shaken Washington’s relations with several countries, made his comments in an “open letter” published in a prominent Brazilian newspaper, Folha de Sao Paulo, in which he described the agency’s activities as potentially “the greatest human rights challenge of our time.”

In the letter, Snowden commended the Brazilian government for its strong stand against U.S. spying.

Brazil, a leading target of the National Security Agency’s activities, has reacted angrily to the spying, which included surveillance of President Dilma Rousseff, her inner circle of senior advisers and Petrobras, Brazil’s national oil company. Rousseff called off a state visit to Washington in October after the revelations of the agency’s operations in Brazil.

Since then, Brazilian legislators have pressed ahead with inquiries into spying by the U.S., relying to a large degree on news reports and testimony by Glenn Greenwald, a Brazil-based U.S. journalist to whom Snowden leaked documents.

The revelations about the agency’s spy programs were first published in The Guardian and The Washington Post newspapers in June, based on some of the thousands of documents Snowden handed over to Barton Gellman at the Post and to Greenwald and his reporting partner, Laura Poitras, a U.S. filmmaker.

David Miranda, Greenwald’s domestic partner who lives in Rio de Janeiro, has helped lead an effort to obtain asylum in Brazil for Snowden, who is now in Russia on a one-year visa.

“He deserves thanks for what he’s done, not a life in prison,” Miranda said, referring to the legal challenges Snowden faces in the U.S.

“Brazil is a big, strong country, I think one of the few nations in the world that could offer asylum to Edward Snowden,” Miranda said. “He’s helped so many nations, and I think mine like all others that have sworn to defend human rights should step forward to help him now.”

Snowden “just wants to continue the work that he began six months ago” when he first handed over documents to Greenwald and Poitras, Miranda said.

However, he “can’t participate in the debate that’s happening now because Russia doesn’t allow him to take part,” Miranda said. “But if he were to be given permanent asylum, particularly here in Brazil … I think he can help the entire world and Brazil understand the situation.”

In his letter, Snowden referred to the spying on Rousseff, who as president decides whether to grant asylum to foreigners, and on surveillance of ordinary Brazilians who might be having extramarital affairs or viewing pornography, activities that could then be used to hurt their reputations.

“American senators tell us that Brazil should not worry, because this is not ‘surveillance,’ it’s ‘data collection,’” Snowden wrote. “They say it is done to keep you safe. They’re wrong.”

Snowden continued: “These programs were never about terrorism: they’re about economic spying, social control, and diplomatic manipulation. They’re about power.”

A spokesman for Rousseff declined to comment on Snowden’s letter and his request for asylum in Brazil, which he had sought in July when he also requested asylum in other countries. Brazil’s Foreign Ministry did not respond to his request at that time, technically not denying it and therefore leaving it pending and open to approval.

A spokesman for the Foreign Ministry press office said it was monitoring the reaction to Snowden’s letter but that it was “not suitable for the Brazilian government nor the Foreign Ministry to respond.”

Venezuela and Bolivia have offered asylum to Snowden, but it is unclear whether their offers meet his conditions. In his letter, he referred to the refusal in July by several European nations to allow the plane of Bolivia’s president, Evo Morales, into their airspace amid suspicions that Snowden was on board.

In Brazil, a Senate committee investigating the National Security Agency’s activities was expected to convene later Tuesday to discuss Snowden’s asylum request.

In July, the Brazilian Senate’s committee on foreign relations and defense unanimously recommended granting asylum to Snowden.

Greenwald said he supported such a move.

“Millions of people in nations around the world have understandably expressed gratitude for Edward Snowden’s courageous whistle-blowing,” he said. “Each of those countries’ governments has the legal and moral obligation to protect him from the persecution to which the U.S. government is now trying to subject him.”

Several members of Brazil’s Congress also have called for Snowden to receive asylum so he could assist lawmakers’ investigation.

Sen. Vanessa Grazziotin, who heads the Brazilian Senate panel investigating U.S. espionage, said Snowden’s letter shows that “he wants to cooperate, but without imposing any conditions.

“His help would be more than helpful, but it all must be done in such a way so as not to jeopardize our relationship with the United States,” she said. “I personally defend the idea that Brazil should grant Snowden political asylum for humanitarian reasons only, not in exchange for information.”

U.S. officials have remained steadfast in their stance on Snowden, accusing him of leaking classified information and saying he should face felony charges in American courts.

Meanwhile, Rousseff has ordered Brazil’s government to take several measures, including laying fiber-optic lines directly to Europe and South American nations, to “divorce” Brazil from the U.S.-centric backbone of the Internet that experts say has facilitated spying.

She also recently joined Germany in pushing for the United Nations to adopt a symbolic resolution that seeks to extend personal privacy rights to all people.

Information for this article was contributed by Simon Romero of The New York Times and by Bradley Brooks, Jenny Barchfield and Stan Lehman of The Associated Press.

Front Section, Pages 6 on 12/18/2013