ANDRES OPPENHEIMER

Here's the latest theory about the power struggle taking place inside Cuba: It's not between President Fidel Castro and the dissidents, nor between modernizers and conservatives within the ruling Communist Party. It's between Fidel and his brother Raúl.

That's one of the most interesting conclusions of Ricardo Pascoe Pierce, a leftist politician who served as Mexico's ambassador to Cuba for two years until late 2002, in his book En el filo (On the Brink). The 500-page book is scheduled to appear in Mexican bookstores (in Spanish only) starting next week.

I read the book as soon as I got it. Pascoe is one of the smartest thinkers of Mexico's old-guard nationalist left, and I wanted to see if living on the island had changed his generous view of the Castro dictatorship.

At first, I found the book revoltingly sympathetic to human rights abusers.

By his own account, Pascoe spent his days in Havana at cocktail parties with fellow ambassadors and Cuban officials, and never once met with opposition or human rights leaders. That would have hurt his efforts to build good relations with the Castro government, he explains (even if his Cuban counterpart in Mexico was spending most of his time meeting with Mexican oppositionists).

Most of the book is a daily diary of Pascoe's lonely battle to prevent his boss, then Foreign Minister Jorge Castañeda, from supporting a resolution against Cuba at the United Nations Human Rights Commission (''That would be a cultural surrender to the United States,'' Pascoe writes) and to withstand Mexican government pressures to build bridges with Cuba's peaceful opposition.

OFFICIAL LINE

Pascoe's first diary entries, in February 2001, show a man who had bought the official propaganda line that Castro is a benign autocrat (``the father of all Cubans''), an untiring worker, a meticulous analyst and -- most importantly -- a leader who ``never lies.''

But, as time goes by, the reality of Cuba's repression and government hypocrisy begins to creep into Pascoe's dissident-proof office.

By June 2001, Pascoe writes that ''the essential discontent with the regime is huge.'' By November, he is told by a visiting Nicaraguan leftist leader that all of her Cuban friends' children ''want to leave this country.'' In early 2002, he shockingly discovers the unthinkable: ''Fidel'' is a blatant liar, who knowingly distorts the facts.

''They are blinded by their omnipotence,'' Pascoe writes in March 2002. ``They believe they are gods.''

Pascoe, who still defends his decision to talk with only one side of the Cuban drama, says that Castro's June 23, 2001, fainting during a public speech has set off a fierce internal power struggle in Havana.

The incident caused Fidel Castro to change his previous plans to turn over the government to his brother Raúl, because a government poll conducted that day revealed that the Cuban people did not want Raúl to take over, he says. Pascoe heard about the poll from a well-placed member of Fidel Castro's private office, he says.

DELEGATING POWERS

From then on, Fidel Castro began to delegate growing powers to economic czar Carlos Lage. Raúl Castro was furious and began to act increasingly on his own, often hiding crucial information from his own brother, and sometimes mocking him in public.

Both Raúl Castro and Lage favor an economic opening, Pascoe says. But much like what happened in post-Soviet Russia, the two are merely fighting for ''their areas of influence within the economy.'' Raúl Castro runs the tourism and aviation industry, while Lage runs public works, oil, electricity and mining companies.

It's very interesting, but I wonder whether it will matter. If Latin American history taught us any lesson, it's that after many decades of totalitarian rule, the pendulum always swings to the other side. Both Raúl Castro and Lage may end up as an asterisk in Cuba's post-Castro era, as the last vestiges of an old regime everybody will want to forget.

As the Cuban government's official poet Roberto Fernández Retamar reportedly told Pascoe in a private conversation revealed in the book, Castro's recent decision to change the Constitution and declare socialism irreversible was ''absurd,'' because ''everything we have seen in recent years is that everything is reversible in this world.'' I couldn't have said it better.