A fierce ocean storm slammed a 200-foot-long dredge into the only bridge to one of North Carolina's Outer Bank islands early yesterday, causing several hundred feet of roadway to tumble into the sea and stranding 5,000 people without power, telephones or direct access to the mainland.

No one was injured as large sections of the bridge across Oregon Inlet collapsed in a fiery 2:21 a.m. explosion after the dredge Northerly Island snapped the high-voltage power cables to Hatteras Island.

Four of the 10 crew members on the dredge scrambled up the bridge to safety. The rest remain on board the vessel, which is trapped in the bridge pylons.

Officials said it could take six months or more to repair the 2 1/2-mile-long span that links the island with the Nags Head area. "There is no way to get across that bridge. It's gone, collapsed," said Gwen White, Dare County public information officer.

White said officials were worried that the trapped ocean-going dredge would destroy more of the span before the heavy seas and gale force winds subsided. The winds, which peaked at gusts of 90 mph, coupled torrential rains with surging seas, causing water to wash across Hatteras at several points. Transportation along the narrow island was impossible, she said.

North Carolina Gov. James G. Martin (R) visited the bridge yesterday and promised the state would immediately seek a contractor to repair the soaring, 28-year-old bridge, which already was threatened by severe erosion. A spokeswoman for the Dare County government said officials expect emergency ferry service would be established near the bridge and that utility crews could quickly restore power and telephone service to the island.

The storm brushed along the Atlantic coast and caused flooding and power outages in the Virginia Beach area. It was the type of storm that experts have warned can cause severe erosion problems to the fragile barrier islands that line the East Coast.

Dare County officials said yesterday they had no immediate reports on the erosion damage on the Outer Banks but said the heavy seas and winds could have done considerable harm to the beaches there. Robert Young, a researcher with a Duke University group that has monitored beach erosion along the North Carolina coast, said he believed the storm may have moved up the coast too rapidly to have caused extensive damage.

The historic candy-striped Cape Hatteras Lighthouse, which sits on one of the most exposed points on Hatteras Island, survived the storm, according to George Berklacy, a spokesman for the National Park Service. The service, which maintains the tower and the nearby Cape Hatteras National Seashore, has rejected suggestions that the lighthouse should be moved inland for safety.

Berklacy said campers had to be evacuated from the seashore because of high water and that those remaining there would be urged to leave the island as soon as transportation is available.

Hatteras Island is a 70-mile long elbow-shaped spit of sand that juts into the treacherous waters known as the "Graveyard of the Atlantic." In recent years, the island has become a major East Coast resort and developed with so many summer homes that environmentalists have voiced fears that the island, a few hundred yards wide at some points, may be overbuilt.

During the summer the island can have more than 100,000 residents, an official said.