BY ANDRES OPPENHEIMER

  U.S. officials believe that Cuba's execution of three ferry hijackers Friday, coupled with the biggest wave of repression against peaceful dissidents in more than a decade, may be an effort to strengthen political control by the regime of President Fidel Castro in the face of growing difficulties.

  ''I think the guy is scared,'' a well-placed U.S. official in Washington said. It is not unusual for Castro to step up repression in times of economic or political crisis as a way of sending a strong signal to potential opponents that his regime will not tolerate any insubordination, other officials said.

  Indeed, things are not going well for the Cuban regime. Among Castro's biggest troubles are a falling economy, growing uncertainty over the success of U.S. congressional efforts to lift the U.S. trade embargo and a growing and increasingly assertive dissident movement.

  To boot, there are the televised images of the falling statues of former Iraqi dictator Saddam Hussein broadcast around the world -- hardly a morale booster for Castro's loyalists.

  Cuba's economy, which had rebounded in the late 1990s after a dramatic fall in 1989, is once again in trouble.

  Tourism, the island's main source of income in recent years, has been damaged badly by the worldwide decline in travel since the Sept. 11 terrorist attacks and by the faltering world economy. The number of tourists going to Cuba fell by 5 percent last year and is expected to remain stagnant or fall again this year.

  Cuba's exports fell from $1.7 billion to $1.4 billion last year and are expected to fall again this year. By comparison, Cuba's exports were at $5.4 billion a year before the collapse of the Soviet bloc in 1989.

  To make things worse, the recent rise in world oil prices is badly hurting Cuba, which has to buy abroad more than half of the oil it consumes.

  ''The economy is deteriorating,'' said Jorge Perez Lopez, an economist with the Association for the Study of the Cuban Economy. ``The engines of growth have slowed down, and the prospects look dim in the short and medium term.''

  EMBARGO ISSUE

  In addition, efforts in the U.S. Congress to lift the U.S. trade embargo on Cuba, which have won growing support in recent years, don't seem to be getting anywhere.

  Despite Castro's relative success in gaining anti-embargo votes among Midwestern farm state legislators, congressional efforts to lift the embargo have been derailed time and again.

  President Bush has vowed to veto any law that relaxes the U.S. trade sanctions, and prospects of an anti-embargo congressional majority that could overturn a veto look dimmer after this month's harsh prison sentences for more than 75 peaceful dissidents in Cuba.

  Making an argument that is sure to be heard again, Sen. Joseph Lieberman, D-Conn., condemned the executions Friday night and said: ``Over the last few years, some succumbed to the comforting illusion that we could go easy on Castro. That was naive, and it was wrong . . . We must never waver and never yield until the people of Cuba taste liberty.''

  ''Castro may have given up hopes on any change in U.S. policy, and may have decided that he didn't have much to lose by launching a massive wave of repression,'' one U.S. official said.

  Meantime, a peaceful opposition movement is gaining unprecedented support on the island and international recognition abroad.

  The Varela Project, a home-grown movement that presented 11,020 signatures of Cubans on the island demanding a referendum on political and economic freedoms, has undermined Castro's claim that opposition to his revolution comes from Miami and that Cubans on the island support his regime.

  Since the petition was presented to Cuba's National Assembly and was applauded by former President Jimmy Carter during a visit to the island last year, leaders of the peaceful opposition movement have gathered more than 30,000 signatures, Varela Project organizers say.

  SUCCESSION MOTIVE?

  Some experts add that Castro, who is 76, may feel that he needs to eradicate any possible opposition in order to carry out his goal of being succeeded after his death by his younger brother, Raúl.

  ''It's going to be hard for Fidel to transfer power to Raúl, who doesn't have his charisma, with an opposition that grows by the day,'' said Andy Gomez, a Cuba specialist with the University of Miami.

  "The harsh measures we saw this week are part of a hardening trend that has been going on for some time, and that has a lot to do with Castro's succession.''