BY ANDRES OPPENHEIMER

Fidel Castro's latest comments about last weekend's 34-country Summit of the Americas seem to support a growing theory among U.S. and Latin American leaders -- that there is a split between Cuban leader Raúl Castro and his nominally retired brother Fidel.

Speculation of a non-declared power struggle at the top of the Cuban regime may have helped to bolster President Barack Obama's hopes at the summit in Trinidad about ''a new beginning'' in U.S.-Cuba ties.

At his news conference at the end of the summit on Sunday, Obama praised Raúl's remarks in Venezuela last week, in which the Cuban leader had stated that Cuba is willing to talk with the United States about ''everything,'' including human rights and political prisoners.

Obama said Raúl's remarks were ''a sign of progress.'' Secretary of State Hillary Clinton welcomed his ''overture.'' And U.S. Deputy National Security Advisor Denis McDonough told me that Raúl's admission that Cuba may have made mistakes in the past ``strikes me as a degree of candor that we haven't seen heretofore.''

But this week, Fidel Castro poured buckets of cold water on U.S. and Latin American leaders' speculation that we may be at the threshold of a new chapter in U.S.-Cuban relations. The former Cuban leader, who retired in 2006 but maintains loyalists in key positions of power, appeared to contradict his younger brother in written ''reflections'' published by Cuba's official press this week.

On Tuesday, Fidel wrote that Obama had ''misinterpreted'' Raúl's remarks about Cuba's willingness to discuss human rights issues. According to Fidel, Raúl meant to say that Cuba would free political prisoners if the United States frees five Cubans convicted in the U.S. of spying for Cuba.

On Monday, in an editorial entitled ''Crazy Dreams,'' Fidel mocked last weekend's calls from some summit leaders for a readmission of Cuba into the Organization of American States, adding that Cuba does not want to be part of the OAS.

At the summit, Latin American leaders told me they believe that Raúl wants to open Cuba's economy, following the Vietnamese model. Fidel, on the other hand, fears that such a path would doom his revolution, they say.

There are concrete signs of Raúl's desire to seek better ties with Washington, Latin American officials said.

Days before the summit, Raúl's government dispatched senior diplomats to Brazil and Argentina to urge their presidents not to risk a rift with the Obama administration at the summit over the Cuba issue. The Cuban emissaries' message was: ask Obama to lift the U.S. sanctions on Cuba, but don't attack the U.S. president to the point where it could create a backlash in the United States and spoil the momentum for a normalization of ties, they said.

Earlier, Brazil's daily Folha de Sao Paulo's prominent columnist Clovis Rossi suggested in an article that Raúl is telling foreign dignitaries that he is his own man. According to the April 12 column, Raúl told Chilean President Michelle Bachelet during her recent visit to Cuba, ``You have to understand that there are two very different Castros here.''

Are the two Castros fighting among themselves, I asked Norberto Fuentes, author of The Autobiography of Fidel Castro, who was close to the Castro brothers before he went into exile in 1994.

''They fight all the time, but at the end of the day they rule together,'' Fuentes said. ``And right now, Fidel's health has improved, and he's running the show.''

According to Fuentes, Fidel has sabotaged every U.S. effort to improve ties with Cuba over the past 50 years and he needs confrontation with Washington to justify his regime's absolute hold on power.

My opinion: Obama deserves credit for offering a carrot to Raúl Castro, and waiting to see whether the Cuban leader bites.

But I'm not too optimistic -- unless Fidel's health takes a turn for the worse -- that there will be a positive response from Cuba. There are two different Castros on the island, but the one in charge is the one we've seen lately looking at the camera with wide eyes and wearing the Adidas tracksuit. And he's not likely to change course this late in the game.