By GINGER THOMPSON and JOSEPH B. TREASTER
 
AVANA, Sept. 12 - Hurricane Ivan hammered the Cayman Islands on Sunday with winds that moved like bulldozers at 155 miles per hour, as thousands of people in Cuba and Florida braced for one of the most powerful storms to boil up out of the Atlantic.

Ahead of the storm, Cuba, the most populated island in the Caribbean, evacuated nearly one million people to shelters and moved truckloads of food into fortified warehouses.

President Fidel Castro spent more than two hours Saturday night on state television with high-ranking military officers and civil defense officials to inform people about the hurricane's magnitude and course. They said they expected the storm to hit the western tip of the island, known for producing some of the highest quality cigars in the world. But, Mr. Castro said in the address, "The country is prepared for this hurricane."

In Florida residents of the Keys expressed relief that forecasters now expected the hurricane to skirt to the west, bypassing them and charging up the Gulf of Mexico to the Panhandle region of the state. But Jimmy Weekley, the mayor of Key West, said he was holding firm to his mandatory evacuation order.

"My gut feeling is that if this storm takes just a little wobble toward the east, it could be right back here," Mr. Weekley said Sunday afternoon. On Sunday, Gov. Jeb Bush declared a state of emergency.

Over the last week, Hurricane Ivan left a trail of death and destruction during its slow march past Grenada, Venezuela and Jamaica. The authorities say Hurricane Ivan is the sixth-strongest Atlantic hurricane ever recorded. At least 65 people have been reported killed, and the authorities expect that number to rise.

On Sunday, Hurricane Ivan, a Category 5 storm, battered the Cayman Islands, tearing roofs and uprooting trees three stories tall. By the time the hurricane's eye was trained toward this island, some 90 miles south of Florida, Cubans had begun calling it Ivan the Terrible. More than 800,000 people have been evacuated from low-lying areas, the official Prensa Latina news agency reported. But Hurricane Ivan has a long reach. And the authorities predicted its churning outer winds would wreak havoc across the rest of the island.

"Cuba will be ready," Mr. Castro, wearing his signature fatigues, said in his television address on Saturday night to this nation of 11 million people.

The storm is the second to hit Cuba in a month. The coastal highway between Havana and Mariel is still littered with telephone poles, billboard and electricity towers toppled by Hurricane Charley in mid-August.

"The last storm took my roof,'' said Iraimie Reyes, sitting on the concrete floor of a government-run shelter. "This time, I expect it to take my house. I don't expect to have anything but the clothes I am wearing when this is over.''

In Miami, officials at the National Hurricane Center said that Cuba could be hit especially hard by Hurricane Ivan. Meteorologists examined glowing orange and red blobs on satellite images showing that sea temperatures between the storm and Cuba were among the warmest in the Caribbean, well above 80 degrees. Those conditions would feed energy into the hurricane and could easily make it a Category 5 monster when it struck, they said.

"It's going to be a panorama of desolation," said Rafael Mojica, a hurricane expert at the center. He said that Guam was about the only place on earth with building codes sufficiently stringent to endure a worst-case hurricane.

Cuba has seen a string of strong storms in the last few years, after a dearth of hurricanes for several decades. The flat land along Cuba's southwestern coast means that the tidal surge pushed by such a storm would add to the destruction from winds that can make such a hurricane's wake "like that of a thousand tornadoes," Mr. Mojica said.

At 11 p.m. on Sunday, the center of Hurricane Ivan was 175 miles southeast of the western tip of Cuba, according to the National Hurricane Center. It had maximum sustained winds of 160 m.p.h., with higher gusts. If the storm stays on its current track, its center is expected to pass near or over the western end of Cuba on Monday afternoon or evening, the Hurricane Center said. Hurricane-force winds extend outward from the storm's center for 90 miles and tropical-storm-force winds for 200 miles

The hurricane began battering Grand Cayman Island, the main island in the group, on Sunday morning, flooding homes, ripping off roofs and toppling trees and power lines. "We know there is damage, and it is severe," Wes Emanuel, a Cayman government spokesman, told The Associated Press while the islands were under siege.

In a telephone interview with the news agency from a fifth-floor building in George Town, the capital of the Cayman Islands, Justin Uzzell, 35, said in the middle of the hurricane: "It's as bad as it can possibly get.''

"It's a horizontal blizzard," Mr. Uzzell said. "The air is just foam."

Government officials in the Cayman Islands said they were worried that the hurricane's drenching rains would touch off mudslides, just as they did earlier in Jamaica.

In Jamaica the authorities said mudslides were expected to continue in the central hills and mountains for several days as sporadic heavy rain continued. Prime Minister P. J. Patterson of Jamaica met with emergency officials at his offices in the white-washed Jamaica House on Sunday afternoon to get their assessments of damage after a flyover by helicopter and examinations by boat and car of remote areas. Mr. Patterson said he was holding off on a damage estimate until he could meet with his cabinet on Monday.

In Kingston, the capital of Jamaica, some houses and businesses lost roofs, and a few had shattered windows, but the most widespread impact of the hurricane appeared to be fallen trees and power lines. Throughout the city on Sunday, homeowners were clearing debris from their yards Sunday, repairing roofs and putting away shutters and plywood covering.

Though the wreckage on much of the island consists of uprooted trees and ripped-off roofs and awnings, government officials cautioned that they were getting reports of some pockets of heavy damage.

Emergency officials said they had no reports from two parishes, the rough equivalent of counties in the United States, and were worried that serious damages might have occurred in those places. One of them was Westmoreland on the western tip of Jamaica, where Negril, one of the main resort towns, is situated. The other is the parish of St. Elizabeth on Jamaica's south coast, which took the brunt of Hurricane Ivan's powerful winds. By late Sunday afternoon, Jamaica's skies were generally clear, and much of the country was returning to normal. Electricity was restored to parts of Kingston and officials said other parts of the country would be getting power shortly.

The airport in Montego Bay resumed operations Sunday, but the airport in Kingston remained closed because the road to the airport was still under water.

In Jamaica, at least 15 people have been killed. In one neighborhood in the southern-most knob of Jamaica, Portland Point, eight people drowned in storm surges and north of Kingston, a father and three children died in a mudslide that buried them in their home.

Ginger Thompson reported from Havana for this article, and Joseph B. Treaster from Kingston. Andrew C. Revkin contributed reporting from Miami and Joel Brinkley from Key West.