By Marc Frank

HAVANA (Reuters) - Former Cuban President Fidel
Castro turns 84 Friday, back in the limelight with a
barrage of public appearances and nuclear war prophecies that
raise questions about his influence on the socialist-ruled
island.

But opinions are divided about whether his flurry of
appearances since July 7, breaking four years of seclusion
after a 2006 illness, will help or hinder prospects for change
in one of the world's last one-party communist states.

For the last six weeks, Cubans have gaped and foreign
diplomats and analysts scratched their heads as the historic
leader of the revolution emerged from a long period in the
shadows to preach dire warnings of a nuclear apocalypse to
local economists, diplomats, intellectuals and lawmakers.

Castro in 2008 formally handed over the Cuban presidency to
his younger brother, Raul Castro, who is 79, but he retains his
post as first secretary of the powerful Cuban Communist Party.

Before the latest appearances, intestinal surgery in 2006
and illness reduced his sightings to glimpses in photos and
videos meeting guests at home, and to a stream of written
essays, mainly on world affairs, published by state media.

Images of a relatively healthy and lucid Castro dressed in
his trademark military olive green flashed across world TV
screens Saturday when he read a short live speech before the
National Assembly, diplomatic corps and foreign journalists.

Castro called on U.S. President Barack Obama to avert a
nuclear war by not enforcing U.N. sanctions aimed at
controlling Iran's nuclear activities through inspection of
Iranian cargo ships. He asserts Tehran would respond to such an
inspection attempt by sinking the U.S. fleet, triggering a
conflict he earnestly urges world leaders to avoid.

These headline-grabbing utterances have stolen the
spotlight from his more low-key brother Raul, causing many to
ask who is calling the shots in Cuba's secretive leadership.

"There has been much speculation as to what Fidel Castro is
up to. Some speculate that he and his brother Raul have divided
tasks and duties: Raul will handle domestic affairs, Fidel
foreign policy. But that seems most unlikely," said Wayne
Smith, a former U.S. diplomat who opened the U.S. Interests
Section in Havana during the Carter administration.

One communist party cadre, who asked not to be named, said
Fidel Castro was strengthening his brother's government at a
difficult moment both in domestic and foreign policy.

JUST ADVISORY ROLE?

"Fidel's presence has two objectives: to back Raul's
efforts to modernize the economy by showing he is still very
much around and therefore approves, and to counter the negative
international media coverage we received over human rights this
year by shifting attention to the United States' two soft
spots, war and the environment," the official said.

Raul Castro's government suffered foreign condemnation
earlier this year following the hunger strike death in jail of
a dissident prisoner. In a deal last month with the Roman
Catholic Church, it agreed to release 52 political prisoners.

Most observers agree Castro is in no condition to govern as
he did for nearly half a century.

In an interview Sunday with visiting Venezuelan
journalists, he himself suggested that his role was largely
advisory or consultative.

"My role is to say what is happening so that others can
decide what to do. You have to understand that the comrades (in
government) are not people I can lead by the hand, what I want
is for them to think things over," Castro said.

Castro's birthday has traditionally been a low key affair,
though no one is taking bets these days that he won't appear
cutting a cake with a few hundred children, as he sometimes did
before taking ill.

Some observers fear that the elder Castro's more active
presence, even though it may not translate into direct
interference, could still slow Raul Castro's cautious efforts
to revive the moribund socialist economy by encouraging more
open policy debate and more individual initiative.

Few doubt that Fidel Castro's steely "Socialism or Death"
mantra put a brake on economic reforms initiated in the 1990s.

"He does not need to strain himself with an executive role,
since he gets to give advice and who in hell is going to say
'no thanks' to his advice," said one western businessman with
interests in Cuba, who asked not to be named.

"Everything will take longer than it otherwise would and
only lowest common denominator measures will be approved".

By and large, many Cubans have welcomed their comandante's
comeback with the respect and affection one might bestow on a
wise old grandfather home after a prolonged hospital stay.

"I don't know what impressed me more. Seeing Fidel again
speaking to the country and world, or his vision of what
humanity faces," school teacher Maria Julia Roche said in a
telephone interview from Eastern Holguin province.

But many young people in Havana were too busy enjoying
their summer vacation to pay much attention, and some opponents
were openly scornful. Cuban dissident blogger Yoani Sanchez
called him "a stuttering old man with quivering hands" in an
opinion piece published by the Washington Post.
(Editing by Pascal Fletcher and Cynthia Osterman)