Secretary of State Hillary Clinton traveled to the 40th Organization of American States General Assembly meeting on Sunday with two priorities, neither of which were published in the meeting's agenda: to shore up support for Honduras' re-entry to the OAS, and to gather momentum behind the Obama administration's drive to impose sanctions on Iran through the U.N. Security Council.

It was a program designed to confront, without naming, the country that has become the greatest challenge to the Obama administration in Latin America -- Brazil.

To be sure, Venezuelan President Hugo Chávez has stood out as the most strident opponent to U.S. policy in the hemisphere since he was first inaugurated in 1999. When the U.S. and Colombia negotiated a defense agreement last year that would give the U.S. greater access to several of Colombia's military bases, Chávez scrapped economic and diplomatic ties with Bogotá. Chávez has relentlessly prodded the Obama administration to ease its economic and diplomatic isolation of Cuba. And now, Chávez is pushing just as hard to keep Honduras excluded from the OAS.

But what gets less attention is that Brazilian President Lula da Silva sympathizes with Chávez's outlook on all of these issues. More importantly, Brazil has become a lot more effective at neutralizing U.S. policy goals in the region than Venezuela.

Lula da Silva has played a key role, for example, in a recent series of direct challenges to the U.S. policy of diplomatically and economically isolating Cuba. In a December 2008 meeting in northeastern Brazil of the Rio Group, a hemispheric union of which the U.S. is not a member, Cuba was invited to join. And at the Obama administration's first hemispheric summit meeting in Trinidad and Tobago in April of 2009, the U.S. agenda was brushed aside, with the event devolving into a chorus demanding an end to the half-century-old U.S. trade embargo against Cuba.

The following June, the meeting of the OAS in San Pedro Sula, Honduras, again abandoned its agenda in order to rescind a 1962 resolution expelling Cuba from the hemispheric body. Cuba has yet to rejoin the OAS, but Lula da Silva called the step a "victory for the Latin American people."

Brazil also opposes the newly announced U.S. position of allowing Honduras back into OAS, maintaining its firm support for a resolution passed last June (.doc) demanding the restitution of former President Manuel Zelaya and prohibiting the recognition of successor governments to the coup that ousted him.

Venezuela predictably lambasted the U.S. position on Honduras' status at the OAS, but there is a key difference between the Venezuelan and Brazilian postures: When Lula rebuffs the Obama administration, he does it with a wink and a smile.

Like Venezuela, Lula also criticized the U.S.-Colombia defense agreement last year, saying it "didn't please" him. But a few months later, he signed his own more-limited security pact with the United States.

Brazil has now taken its challenges to U.S. power beyond the Western Hemisphere, to the international stage. Last month, Lula da Silva negotiated a nuclear fuel swap agreement with Tehran, complicating the Obama administration's efforts to impose U.N. Security Council sanctions on Iran for failing to comply with nuclear non-proliferation accords. True to form, just weeks before negotiating the troublesome deal, Lula cheerfully invited Obama to visit Brazil. (Obama declined.)

Lula's efforts to forestall a new round of sanctions ultimately failed, with a watered-down resolution passing on Wednesday. But the move prompted Clinton to use the OAS meeting as a venue for pushing the administration's Middle East policy.

It also allowed Lula to maintain the moral high ground, by hijacking Obama's image as the cool-headed mediator willing to maintain open lines of communication with anyone. "There are people who don't know how to do politics without having an enemy," Lula said, in an indirect criticism of U.S. policy toward Iran.

The result is that notwithstanding all the underlying tensions, the U.S. and Brazil remain -- publicly, at least -- firm allies. This makes Brazil a much thornier foreign policy problem for the Obama administration. While Chávez's posturing and inflammatory rhetoric appeal to some, he has trouble gaining credibility with political moderates. Lula da Silva, on the other hand, cannot be dismissed as an extremist or an obstructionist, allowing him to more effectively counter U.S. policies that he opposes.

While Lula's deal did not keep the U.N. from hitting Iran with sanctions, and probably will not halt Iran's uranium enrichment, Lula's diplomatic maneuvering clearly marked Brazil's entrance into the club of world powers.

But Brazil's rise is not just the story of a regional giant finally coming of age. It also reflects the foreign policy goals charted over the last eight years by Lula da Silva, whose term ends this year. If Lula's former chief of staff and handpicked successor, Dilma Rousseff, wins in October's presidential election, we can expect more of the same. But if opposition candidate and former President José Serra wins, Obama may well gain a firmer ally.

Serra will face pressure from the Brazilian electorate -- which supports Lula to the tune of 76 percent in a recent opinion poll conducted by Datafolha -- to maintain continuity with the outgoing administration. But the two clearly diverge on foreign policy. At a recent debate before the National Industrial Confederation, Serra criticized Lula's deal with Iran and compared Iranian President Mahmoud Ahmadinejad to Hitler.

If Serra were elected, he would also probably more greatly distance Brazil from the governments of Venezuela and Bolivia, with which Lula da Silva has often dealt pragmatically. In an interview last month with Radio O Globo, Serra took a jab at Bolivian President Evo Morales, saying that the Bolivian government is "an accomplice to Brazil's drug traffickers."

Serra's election would remove the most serious challenge to the Obama administration's foreign policy goals in Latin America, and tip the regional balance of power away from Latin America's far-left bloc. Perhaps then Obama will be more likely to accept an invitation to visit Brazil.

(Roque Planas i World Politics Review)