SANTO DOMINGO, Dominican Republic -- Cuban President Fidel Castro arrived Thursday for a Caribbean summit under an unprecedented security blanket woven of gunboats, a helicopter and thousands of armed guards.

Security officials concerned about reported plots to kill Castro barred all traffic from the 19-mile route from the international airport to Santo Domingo and lined it with police and troops armed with assault rifles.

A helicopter and a fast patrol boat shadowed Castro's motorcade along the coast-hugging route, and two gunboats later patrolled the waters in front of the hotel where Castro and 15 other Caribbean leaders are staying.

Castro arrived aboard one of two matching Cubana de Aviacion jetliners, apparently a precaution against air attacks, and boarded one of three identical black limousines for the ride into the capital.

Scattered knots of 10 to 20 Dominicans waving Cuban flags lined the route, and some 100 radical leftists set up a vigil outside the Jaragua hotel, vowing to protect Castro with their own bodies if necessary.

Dressed in his trademark olive green fatigues, Castro looked fit for the latest of his Caribbean swings designed to shore up commercial and political relations with his closest neighbors.

Castro thanked

President Leonel Fernandez told Castro to ``feel at home'' at an airport ceremony and thanked him for arming a group of Dominican rebels who invaded from Cuba in 1959 in a failed attempt to topple the Trujillo dictatorship.

``I would not have mentioned it,'' demurred Castro, who almost always denies that he armed Latin America guerrillas in the 1960s. ``But it's nothing, what we may have done for you.''

Castro is expected to get warm receptions as he attends a three-day summit of Caribbean leaders to discuss regional issues, and then spends two days touring a nation he said he had ``long dreamed of visiting.''

It is a country that saw Rafael Trujillo assassinated in 1961, a coup in 1963 and a U.S. military invasion in 1965 to quell a civil war that U.S. officials feared would end in another Cuban-styled Marxist regime.

For the next 12 years, anti-communist President Joaquin Balaguer harshly persecuted leftists and blocked relations with Cuba. Balaguer, who ruled for 22 of the last 32 years, left office in 1996.

Fernandez's Dominican Liberation Party, now centrist, was founded as a Marxist party and has long opposed the U.S. trade embargo on Cuba. Fernandez restored full diplomatic relations with Havana in April after a 39-year break.

A low profile

Anti-Castro exiles living here kept a low profile Thursday after two brief clashes with leftist radicals Wednesday. But an exile group from neighboring Puerto Rico said it had asked permission to fly an airplane over Santo Domingo dragging a sign: ``Fidel Castro. Dictator and Murderer.''

``We reject the attitude of democratic governments that invite a dictator'' to visit, said the group, Casa de Jose Marti.

But the reports of plots to kill the Cuban president during his visit make it unlikely that Dominican authorities will allow any anti-Castro group to get too close to the 16 Caribbean heads of government at the summit.

A top Dominican security official Wednesday confirmed that police had arrested a Cuban-born man last week, but said they found no convincing evidence of a plot against Castro. The man's name has not been made public.

``He had a notebook with some notes on Castro's travels, written in pencil, but we found nothing suggesting a plot,'' said Gen. Sigfrido Pared Perez, head of the National Investigations Directorate, the country's FBI.

The man was detained in the western town of Jimani, on the border with Haiti, and claimed he was a diesel motor mechanic on his way to Port-au-Prince to work on a boat motor there, Pared Perez told The Herald. A search of the Santo Domingo home where he had stayed turned up nothing unusual.

The man had overstayed his six-month Dominican visa by one month and was turned over to immigration authorities. He had Spanish travel documents and will probably be sent to Spain soon, Pared Perez added.