Blaze at Pendleton Mostly Extinguished : Brush fire: Firefighters attack by land and air in area where 4,800 acres were scorched. Interstate 5 and the Amtrak line are back in operation.

Firefighters made aerial and land assaults on a brush fire that scorched 4,800 acres in the Camp Pendleton area, extinguishing most of the blaze by nightfall Thursday.

The fire, which broke out Tuesday night, caused commuter chaos Wednesday by forcing a 12-hour closure of Interstate 5 and the Amtrak line. Operations were back to normal by Thursday, and despite all the disruption, officials reported no injuries or significant damage.

Officials of the Marine base and the U.S. Forest Service said the cause of the fire had not been determined. Cpl. Connie Panichi, a Camp Pendleton spokeswoman, said a report that the blaze was sparked by Marines during routine training maneuvers Tuesday night had not been confirmed. “When we conclude our investigation, we will be in a better position to say exactly what happened,” she said.

The strong Santa Ana winds that had whipped the fire out of control died down on Thursday, greatly aiding the efforts of the estimated 500 firefighters who battled the blaze. Water and chemicals were dropped from planes and helicopters to help douse the flames.

The fire was declared contained by 6 a.m. and was expected to be completely extinguished by late Thursday.

Containment of the fire brought sighs of relief from residents who lived near the wind-whipped fire.

Betty Dickson, whose hillside San Clemente home abuts the Marine base, looked outside her living room window Thursday afternoon and noted that it was the first time in three days she did not feel threatened. “There is no smoke, no fire, no red glow . . . that makes me feel good,” Dickson said. As firefighters from Camp Pendleton, the Forest Service, San Clemente and Orange and San Diego counties put out the last patches of fire, base officials provided a new estimate of the damage, saying the fire consumed 4,800 acres and not 7,000 as originally estimated.

It was business as usual for utility companies and other agencies whose operations were affected when the fire roared through the San Onofre area.

The California Highway Patrol was bombarded with calls from motorists who wanted to avoid a repeat of their nightmarish experience Wednesday on Interstate 5. “We’re telling callers that traffic is very light and moving very smoothly,” Officer Patti Gentile said.

Although an emergency alert was called for several hours Wednesday at the San Onofre nuclear power plant, a spokesman said there was no real danger.

“The plant was never really threatened although fire jumped the interstate on the southern side of the plant and consumed some brush there,” said David Barron, spokesman for Southern California Edison, which operates the plant.

At the nearby U.S. Border Patrol checkpoint, spokesman Ted Swafford said damage was minor. Telephone and power service were affected but quickly restored. The plastic grill of an Immigration and Naturalization Service vehicle was singed Wednesday when fire threatened to overrun the facility. But the checkpoint was back in operation by 11 p.m. Wednesday, Swafford said.

Train travelers were affected Wednesday when northbound and southbound trains were halted as winds blew flames across the tracks. But on Thursday service returned to normal.

“We’re in good shape today,’ said Clifford Black, an Amtrak spokesman. “Our trains have to slow down a bit across a 3-mile stretch (that was scorched by fire), but that’s only a precaution, we’re still running on time.”

Panichi said training activities at Camp Pendleton resumed Thursday after a temporary suspension caused by the fire.

Times correspondent Len Hall contributed to this report.