Hurricane David pounded this historic coastal city with 70 mph winds today, knocking down trees and power lines and flooding low-lying streets before heading inland over South Carolina as one of this century's worst Atlantic storms hit the mainland for the second time in two days.

Thousands fled homes along the coasts of Georgia and South Carolina. Another 5,000 in the storm's path had ignored an order to evacuate.

The storm gathered strength as it swept up the coast from Florida, and moved ashore again after 90 mph winds and a 6-foot storm tide lashed barrier islands near the South Carolina-Georgia border. Forecasters warned of flooding in low-lying areas because tides were already running up to 10 feet above normal before the storm surge.

In the Washington area, the outer fringe of David was expected to reach the lower Eastern Shore Wednesday morning. The local effects were unpredictable, although rains, sometimes heavy, are forecast for Wednesday and Thrusday.

Police said damage was light but widespread in Savannah, a colonial city of 120,000 with antebellum houses and museums.

Savannah Mayor John Rousakis said, "we were very fortunate. The hurricane lost some strength as it came inland. Water is cut off, we have some flooding . . . but other than that, even though there are inconveniences now, people are in fairly good shape."

"We have lost power, we're on emergency power," said Danny Smith, director of environmental services at Candler Memorial Hospital in Svannah. "We have lost water, we're bringing in water from the civil defense. It's coming in on tank cars so we'll have drinking water and water to run our boilers."

From Savannah the storm moved inland to the interior of South Carolina passing 50 to 75 miles west of Charleston. Inland residents were warned to prepare for 90 mph winds and up to 5 inches of rain.

Residents of coastal islands from Hilton Hotel to Myrtle Beach were evacuated as the storm bore down.Gov. Dick Riley extended mandatory evacuation orders to all islands and low-lying areas, put the state's National Guard on alert, and said citizens should "stay in their homes and shelters" overnight.

The National Hurricane Center called for hurricane warnings to be posted from Brunswick, Ga., to Cape Fear, N.C.

"A storm surge of 6 feet is on the coast in the Savannah area and will spread up the South Caroline coast this evening," a hurricane advisory said, "This means that tides which are already well above normal because of unusual astronomical influences will be increased another 6 feet by the storm surge.

"This combination will cause very serious tidal flooding along the coast and offshore islands from Savannah to Charleston."

The storm also was expected to spread rains inland, causing serious flooding over most of the Carolinas.

Except for 10 persons stranded in a lighthouse, the island beaches were deserted, said Ed Fogarty, director of civil defense in Savannah. But residents farther inland-- some afraid of looters-- refused to leave their homes.

"I can understand how they feel," Fogarty said. "When this has happened before, people have returned to find everything but groceries gone."

Fogarty said about 50 National Guard troops were standing by to help city and county police patrol the islands and prevent looting.

About 3,000 evacuees from the coastal islands and lowlying areas of the mainland were housed in shelters in Savannah.

"Everybody's bedded down. There's no hysteria," Fogarty said.

Communications to residents were cut briefly when Savannah's radio and television stations went off the air at midday, but power was quickly restored.

The storm had been expected to hit first near Charleston, another historic city where thousands of residents were evacuated. But the National Hurricane Center said David "took a small turn to the west."

In South Carolina, many persons at the elegant Hilton Head Island resort took shelter, and thousands of others were routed from the resorts of Sea Island and St. Simons Island just off Brunswick, Ga.

South Carolina has not been hit hard by a hurricane since Hazel devastated the Myrtle Beach area in 1954, killing one person and causing damage estimated at $27 million.

The two-lane bridge to Hilton Head was closed to traffic and power to the island was shut off. Beaufort County civil defense authorities estimated 2,000 persons had taken refuge in McCracken High School at Bluffton, Patients at the Hilton Head Island hospital were evacuated by ambulance to Beaufort.

"There's not a loaf of bread left in the store," said Billy Powell, co-manager of a James Island grocery. A Charleston department store reported brisk sales of flashlights, radio batteries, cooking fule, camp stoves, lamp oil and hurricane lamps.

A spokesman for the Navy's Atlantic Fleet said units in Norfolk, Elizabeth City, N.C., and South Carolina are at "Condition Three," meaning all military personnel are on board and ready to move out.

North Carolina also was battening down, and coastal residents began leaving low areas. The forecast for southeastern North Carolina called for winds up to 50 mph, along with heavy rains and 8 to 12 foot surf.

About 85 elderly residents were evaucated from nursing homes on Tybee and St. Simons islands on Monday, and a special boat was sent to remove the 150 residents of Daufuskie Island, S.C. Only about 15 of them initially agreed to leave. But today, as the storm bore down, civil defense director Pete Liatakis said they are "screaming for us" now. A Coast Guard cutter was dispatched.

Florida officials were toting up the damage from David's strike Monday on the central Florida beaches near the nation's spaceport at Cape Kennedy.

"We're a long way from beginning to have a feel for what the damage is," said Joan Heggen, secretary of the Florida Department of Community Affairs. "In many of the areas, people can't go back to their homes yet."

Florida Gov. Bob Graham said he would seek federal aid for the heavily damaged areas.

Meanwhile, tropical storm Frederic churned across Puerto Rico, threatening new floods on the already waterlogged island where David left 25,000 homeless.

The National Weather Service in San Juan said Frederic's maximum sustained wind gusts were 60 mph (75 mph would classify the storm as a

"The ground is already saturated and widespread flooding is almost a hurricane). certainty," the weather service said.

The international airport was closed and wide areas of the island were blacked out. Schools were shut but some banks and businesses were open.