Cuban President Fidel Castro has named his top personal aide to replace Foreign Minister Roberto Robaina, tightening his control over foreign policy at a particularly sensitive moment for the island.

Felipe Perez Roque, 34, becomes the only Cabinet member born after Castro came to power in 1959. He is assuming the job at a time when U.S. policies toward Cuba are shifting, opposition to the U.S. embargo is rising and even friendly nations are complaining about Havana's crackdown on dissent.

Cuba's Prensa Latina news agency reported Friday that Castro had replaced the 43-year-old Robaina, foreign minister since 1993, because of ``the need for more profound, rigorous, systematic and demanding work in this sphere.

Although Robaina had long been rumored to be on his way out, Castro surprised analysts by giving the job to Perez Roque, an electronics engineer and former university student leader who has served as his chief of staff for the past decade.

A spokesman for the U.S. State Department said Perez Roque's appointment was unlikely to affect relations between Washington and Havana.

``We do not expect the substitution to have any impact on the nature of U.S.-Cuban relations,'' the spokesman said.

Western business people and journalists who have met Perez Roque describe him as a behind-the-scenes power in Cuban politics, smart and reserved, a conservative but not a Communist ideologue -- and above all, absolutely devoted to Castro.

``He is doorkeeper to the emperor, one businessman said. ``He is one of the guys that makes certain that Castro sees and hears the right things, and what he says reflects whatever the boss says.

Perez Roque's appointment will raise the importance of the Foreign Ministry ``because he has Castro's ear, said Pamela Falk, a City University of New York professor who is writing a book on Cuba.

``But Castro is also making sure that whoever is at the helm of foreign policy knows exactly what he wants -- to open doors without compromising on the big issues, Falk added.

``Maybe this is Castro's way of stiff-arming any chance for improving relations with the United States, because he needs an enemy to stay in power, said Ed Gonzalez, a Rand Corp. analyst who specializes in Cuba.

Cabinet changes are rare

Perez Roque is also a member of the Communist Party's Central Committee and the government's top ruling body, the Council of State, and has a seat in the National Assembly, Cuba's legislature.

Cabinet changes in Cuba are rare and this one seemed particularly unusual because Robaina's staff announced Thursday that he would visit Venezuela, Panama and Haiti beginning next week.

Prensa Latina made no mention of a new assignment for Robaina. It paid him a faint compliment, saying he had ``made the greatest efforts to carry out his job during the time he was in charge.

Robaina has been credited with improving Cuba's foreign relations to their best level in decades, establishing diplomatic ties with many nations after the Soviet bloc collapsed in 1991.

With his trademark rolled-up jacket sleeves, the former Communist Youth Union leader -- who was 37 when he became foreign minister -- projected the image of a new, moderate Cuba open to reforms.
His removal was rumored

But rumors of his impending removal have swept Havana regularly since late 1995, when the easing of the economic crisis sparked by the end of Soviet subsidies allowed Castro to demand a return to communist orthodoxy.

Reforms have been halted or trimmed back, proponents of economic and political openings have been silenced or demoted to almost invisible posts and the government's socialist rhetoric has intensified.

Even usually supportive nations like Canada and Spain reacted angrily in February when Cuba adopted a harsh new law on dissent and convicted four opposition leaders who had criticized the Communists' monopoly on power.

``Robaina's ability to `sell' Cuba has been harmed not by his salesmanship but by the fact that the product he was trying to sell changed, said one U.S. businessman in regular contact with Cuban officials.

Changes in U.S. relations

Castro supporters portrayed Perez Roque's promotion as evidence that the 72-year-old president wants a trusted aide in charge as he explores the possibilities of improved relations with Washington.

But analysts in and out of Cuba said the shift more likely signals a get-tough approach at a time when modifications in U.S. policy toward the Caribbean nation have put Havana in an awkward position.

The Clinton administration has recently adopted a series of measures designed to increase people-to-people contacts and provide more humanitarian aid to Cuba without benefiting Castro's government.

``When you come at me with a saber in your hand I have to defend myself any way I can. But when you put away that saber and try to embrace me, you put me in a difficult situation, one Cuban official said in a recent assessment of the impact of U.S. policy changes.

A recent Gallup poll showed 69 percent of Americans questioned favored restoring relations with Cuba, and 51 percent favored lifting the 37-year-old U.S. embargo on the island.

``Castro needs an enemy to stay in power, Gonzalez said. ``When it has looked like relations with us were about to get better, he has always done something to hold the line.