Cuban American exile protesters on a six-boat flotilla laid flowers just outside Cuban territorial waters this morning and shone mirrors to try to communicate with opponents of President Fidel Castro on the island.

"They are flashing mirrors at this time trying to get a response," said Coast Guard spokesman Petty Officer Jeff Murphy, who was receiving updates from Coast Guard vessels on the scene.

Mirrors were being flashed back, but it was not known if they came from Cuba or if people in Havana saw the protesters' signals.

Murphy said the protest flotilla stopped at a point 12.5 miles off Havana, half a mile outside Cuban waters, and remained safely in international waters at 9:30 a.m., as required by a U.S. presidential proclamation.

The 72 protesters, who had set out from Key West at 12:40 a.m., released a Cuban flag made of red, white and blue flowers into the water.

Ramon Saul Sanchez, leader of the Miami-based Democracy Movement, said beforehand that the aim was to commemorate "those who have died escaping Cuba and those executed by the government."

The protest was held to mark the fifth anniversary of the July 13, 1994, sinking near Havana of a tugboat packed with dozens of Cubans trying to leave the island for Florida, an incident in which about 40 people died. Survivors said the stolen tugboat was deliberately sunk by pursuing Cuban state vessels; Cuba said the sinking was accidental.

In Havana, most Cubans appeared unaware of the flotilla. As on any normal Saturday, fishermen, strollers and tourists mingled on the capital's Malecon seafront drive.

The Democracy Movement has staged a series of flotilla trips since 1995 to protest Castro's four-decade communist rule of Cuba. In the past, Sanchez forcefully asserted his right to enter Cuban territory. But the United States began cracking down on Cuban exile trips after February 1996, when Cuban jets shot down two small planes flown by members of another exile group, Brothers to the Rescue. Four people were killed in the incident.

President Clinton signed a proclamation banning American vessels or aircraft from heading to Cuba without permits.

CAPTION: Democracy Movement boats "Rene Rene," foreground, and "Democracia" get underway after group members threw a wreath next to the U.S. Coast Guard station off Miami Beach on July 4. Yesterday, protesters aboard a six-boat flotilla sent by the Miami-based organization released a Cuban flag made of red, white and blue flowers in international waters 12.5 miles off Havana.