Hurricane Frederic, the most ferocious storm to hit the Gulf Coast in a decade, churned northward today after bludgeoning a 100-mile wide path of destruction.

Frederic, its worst blows already spent, was officially stripped of its hurricane status as it moved inland. But it still packed winds strong enough to snap power lines and pose a continued threat of tornadoes tonight in northwestern Georgia and northeastern Alabama.

Reduced to a "tropical depression" with winds of less than 70 mph as it crossed the Alabama-Tennessee border tonight, Frederic still brought heavy rains to Tennessee, particularly Nashville, and then on into Kentucky.

The front edge of the storm is expected to pass well to the west of the Washington area, but the capital region is expected to receive some heavy showers Friday.

Frederic's center is expected to be near Cincinnati Friday morning and near Buffalo, N.Y., Friday night.

Governors of Florida, Mississippi and Alabama estimated damage at several hundreds of millions of dollars as wide areas of the Gulf Coast remained semi-paralyzed without power or water.

President Carter is scheduled to fly to Mobile Friday morning and set out from there on a two-hour trip by helicopter across the coastal strip that was bloasted most heavily by the storm.

Carter's journey, the White House said, will permit him "to access the efficacy of government programs in dealing with the hurricane," and will be "an appropirate gesture to display his personal concern."

The White House yesterday circumvented normal procedures in declaring 30 counties along the Golf Coast in Mississippi, Alabama, and Florida "major disaster areas," a determination that makes residents there eligible for a broad range of federal help. The administration made the disaster-area designations over the telephone early today, foregoing the paperwork and on-site inspections normally required.

With some 10,000 telephones out of service in the storm-wracked areas, emergency relief coordinators struggled futilely all day to gather complete information on the damage Frederick wrought along the Gulf.

At 3:30 this afternoon, White House aide Jack Watson, who has acted as Carter's personal adviser on the hurricane, announced that Frederic had killed two people. A half-hour later, the Federal Emergency Management Agency put the number of deaths at eight.

Given the dearth of clear information officials were reluctant to put a value on the extent of damage. John Macy, the head of the emergency agency, said damage estimates made public immediately after most disasters "have tended to be inflated and therefore somewhat misleading."

Frederic with peak winds estimated at 130 miles per hour, apparently did not reach the distructive force that marked Hurricane Camille, which struck the Golf Coast in 1969. Camille's full force was never determined because the storm destroyed all wind gauges in its path, including some that measured up to 210 m.p.h.

Frederic has not proved as ruinous as last week's hurricane, David, did in the Carribbean. But in the continental United States, Frederic has already brought far more destruction than David did in its entire course across the country.

Macy, of the emergency agency, estimated that 500,000 people had been driven from their homes in Florida, Alabama, and Mississippi.The people hit hardest, however, seem to be those who were in the path of the storm as it came roaring up Mobile Bay Wednesday night.

Frederic directed its harshest blow at Mobile and the coastal areas to the south late Wednesday night and early this morning, pounding them with winds often exceeding 100 miles an hour.

Huge pine trees snapped like toothpicks. Small shopping centers were leveled. Scores of mobile homes were ripped apart and upended. Roofs flew off businesses like box tops.

Casualties and injuries, however, were surprisingly few, a fact civil defense officials attributed to the early evacuation of about 400,000 residents. The highest unofficial death count of eight included at least one person killed in a traffic accident before the storm actually hit.

"It's a miracle," said Alabama Gov. Fob James. "We could just as well have had 200 deaths with the winds we recorded.

Mobile looked like someone had passed through it swinging a giant sledgehammer from side to side. Huge freighters in drydock were tossed about. Dozens of 200-year-old oak trees on historic Government Street were left shredded and uprooted. Almost every downtown business suffered some damage, making an early morning round of looting easy. Broken glass and fallen power lines were everywhere.

"WeVe never had anything like this, not anything in my 60 years," said Emile Zoghby as he picked through the rubble in the department store his family had operated on Dauphine Street for four generations.

"We took all the precautions. But it didn't do much good," he said. "This street was Old Mobile. Now look at it."

Half of the store windows on the downtown street were broken. Debris was piled high. One cross atop the Cathedral of Immaculate Conception, Alabama's oldest Catholic Church, was tilted at a precarious angle.

Eddie McGiney surveyed the scene from the corner two blocks away. "I believe the good Lord was just warning his people to be more faithful," he said. "If they don't get better, they can expect something worse than this to happen."

A mile away, Vernon Linam hung a makeshift banner on his gun shop. "Frederic, go to hell," it said.

After flying over stricken areas in Alabama by helicopter, James said the most severe damage occurred at the resort city of Gulf Shores. "Houses have disappeared. Businesses have been destroyed and crops have been damaged," he said in an interview. "If you can imagine a stretch of beach that a few days ago had 500 beautiful homes and motels and now 80 percent of the homes have disappeared and another 14 percent or so are damaged, you'll have a good idea of what it's like there."

James said it was impossible to estimate the extent of damage in Alabama. Mississippi Gov. Cliff Finch, who rode a state police car into 90-mile-an-hour winds, said damage in his state could be about $150 million. Florida Gov. Robert Graham estimated damages would exceed the $95 million in wreckage left when Hurricane David hit last month.

The area hardest hit by Frederic was bounded roughly by Gulf Shores on the east and Pascagoula, Miss., on the west. Winds occasionally gusting to 90 miles an hour hit a considerably larger area, and one woman reportedly died when her boat capsized in Pensacola, Fla.

Unlike 1969, when many people were unprepared for Hurricane Camille, which killed 253 people, the Gulf Coast was ready for Frederic. Most of the affected area had been evacuated for hours before it struck.

Even so, Wednesday night had many hair-raising moments. David Oescuger Jr. and his parents, for example, were getting ready for bed when a tornado-like wind hit their mobile home near Gulfport.

"We were 18 miles from the beach and we had the trailer tied down. We thought we were safe," he said. "But the trailer started rocking and shaking. All of a sudden the roof just ripped right off."

The family climbed out into a 70-mile-an-hour gale and driving rain, threading their way to safety over broken power lines, and fallen trees.

Pascagoula suffered among the heaviest damage. "I'd say there is not building in Jackson County [which surrounds Pascagoula] that does not have damage ranging from minor to total," said Ken Phillips, director of county disaster relief.

Many residents didn't realize the extent of the damage until they reached their homes or businesses after spending the night in makeshift evacuation centers.Jack Higgins found his three and a half-year-old auto store in Pascagoula completely ruined.

"It could have been worse, I damn near stayed in there last night," he said. "I never would have survived."