CHARLESTON, S.C. (AP) _ Hundreds of National Guardsmen patrolled ravaged streets against looting today, and police reported more than 90 arrests as residents returned to begin the long task of rebuilding from Hurricane Hugo.

Chainsaws buzzed, crews worked around the clock to restore power and telephone communications, and insurance agents across the Carolinas braced for claims that could run into the billions from the region's most devastating hurricane in 30 years.

''It is the worst storm, the worst disaster, I've ever seen anywhere,'' Gov. Carroll Campbell said after surveying the destruction by helicopter. ''We're going to be a long time digging out of this and rebuilding.''

The hurricane was blamed for 18 deaths in the Carolinas and two in Virginia.

In the six hours Hugo and its 135 mph winds surged through South Carolina, it flattened dozens of homes and buildings, snapped trees, twisted bridges and washed scores of boats ashore. Mayor Joseph P. Riley Jr. said damage in his 3- century-old city alone might reach $1 billion.

''There's just destruction everywhere,'' said Riley, who imposed a 7 p.m. to 7 a.m. curfew.

Police reported isolated cases of looting. Fifty people were arrested in Mount Pleasant, across the Cooper River from Charleston; 12 in North Charleston; and at least three in Charlotte, N.C. In Charleston, police Sgt. Thomas Gardner said today that 27 people were arrested Friday and early today for looting and one for violating curfew.

''It was very quiet last night. I left at 1 a.m. and the only thing I saw were police cars and National Guardsmen,'' Gardner said. Two people from New Orleans, he said, were posing as relief workers who then would take people's possessions; they had not been charged yet.

The governor deployed 2,600 National Guardsmen to patrol streets, enforce the curfew, help remove debris, purify water and perform other duties.

At a news conference today, Riley said power should be restored by tonight at hospitals, but he could not estimate when residents might get power. Mail delivery could resume Monday, and he recommended that people boil water before drinking it.

Up to half a million customers across the state were without power as of late Friday. In inland Columbia, people lined up at an ice warehouse with coolers. Some areas of Charleston were without water, and residents were told to boil their drinking water.

Two hundred miles inland, Charlotte, N.C., also sustained heavy damage, and nearly 80 percent of the customers in the city of 375,000 were still without power this morning, said Duke Power Co. spokesman Joe Maher.

There were 14 deaths in South Carolina from the storm itself, related traffic accidents, and heart attacks suffered during cleanup, according to the state Emergency Preparedness Division. In North Carolina, three deaths in the Charlotte area were blamed on the storm, and a 6-month-old baby died in Union County when a tree crashed into a house.

Two people were killed by Hugo after it moved into Virginia as a tropical storm. In the Caribbean, where Hugo first touched land, the storm killed at least 27 people and left 50,000 homeless.

''All things considered, we lucked out in a lot of ways,'' said Chipp Bailey, spokesman for Mecklenburg County Emergency Management in Charlotte, where the most serious injury reported was a broken pelvis suffered by a woman when a tree crashed through her roof.

The hurricane and its tidal waves of up to 17 feet smashed ashore at Charleston late Thursday. After being downgraded to a tropical storm, Hugo advanced farther west than expected, whisking through Virginia, West Virginia, Ohio and western Pennsylvania, where the National Hurricane Center stopped tracking it.

By the time it reached Pittsburgh on Friday night, Hugo was generating winds under 40 mph and was no longer classified as a tropical storm. As it fizzled early today, Hugo's dying remnants darted through Canada's St. Lawrence Valley and became lost in another weather front, according to meteorologist Joe Harrison of the National Weather Service in New York.

''We really can't find it anymore,'' Harrison said.

President Bush declared seven South Carolina counties - with a total of 750,000 residents - a disaster area. The declaration frees up federal aid for housing, loans and grants for rebuilding.

Hundreds of insurance adjusters have come to South Carolina to process the damage claims, but it will be days before they begin to catch up, said state Insurance Commissioner John G. Richards.

Along the coast, Folly Beach, Isle of Palms, Pawley's Island, Myrtle Beach, Cherry Grove and Garden City were devastated.

''Garden City for all practical purposes is gone,'' said Horry County administrator M.L. Love after he toured the small unincorporated town near Myrtle Beach. He said damage there could run in the hundreds of millions.

Residents of the Isle of Palms and Sullivan's Island, which were among the hardest-hit barrier islands, were kept from even inspecting their homes because the Ben Sawyer swing bridge - the only link to the mainland - was knocked out. About 100 boats that had been berthed at one marina were ''stacked up like cordwood,'' said Ben Moise, a state Wildlife and Marine Resources Department official.

Pawley's Island had a 100-foot channel of water through it.

''There are now two Pawley's Islands, if you will,'' pilot Jack Sellers said after flying over the island.

Although the Pentagon had dispatched planes and ships from Charleston's Air Force and Naval bases as Hugo approached, the installations suffered perhaps $50 million in damage, said Sen. Ernest Hollings, D-S.C.

Charleston, a city of about 65,000 people, took the full force of Hugo.

Most of the historic antebellum mansions facing Charleston Harbor weathered the storm, but Fort Sumter, the first Union stronghold fired upon by the Confederacy at the beginning of the Civil War, suffered $1 million damage when a 17-foot wall of water roared over it, federal officials said.