Authorities are investigating an early morning fire that rousted a Fairfax County couple from their home yesterday as another of the Washington area's string of arsons.

The regional arson task force linked the fire to a string of more than 35 others set by a serial arsonist or arsonists. Fires have been set in Maryland, the District and Virginia at similar times of day and using similar methods on the exteriors of homes.

Yesterday's fire, about 4:30 a.m. in the 3400 block of Beechcraft Drive in the Hybla Valley area of Fairfax, could have been disastrous had it not been for a neighbor across the street who happened to look out his window.

Alexander Thomas, a carpenter, was sleeping, and his wife, Neely, a child caretaker, was in the bathroom when the fire started at their home. The neighbor, Rafael Perez, saw the blaze through his front window as he was preparing to leave for work.

Perez, who typically wakes up at 4 a.m. for his cabinetmaking job, which begins at 5 a.m. in Lorton, said he saw flames shooting upward from the side of the Thomases' home.

"I called 911 and ran across the street and knocked on their door. Then I don't get an answer. Then I knocked on the window, and the lady answered," Perez said. "I said: 'Your house is on fire! Come on! Get out!'

"She checked the fire and she called her husband," he said.

Alexander Thomas said he emerged from his four-bedroom home as Fairfax County fire and rescue personnel arrived. He said firefighters used his water hose to extinguish the fire.

"When we came out, the fire was low to the ground. There's no way it could have started if someone didn't do it," Thomas said. "I'm very shocked. It's hard to believe it's me. [The arsonist's attacks] are happening to me."

Prince George's County Fire Chief Ronald D. Blackwell, who heads the arson task force, would not say how the fire was set. He said the home's aluminum siding resisted the flames, which left damage along the outside.

Authorities are releasing few other details about the fire, saying it could hurt their investigation and potential prosecution.

Yesterday's fire was the 38th serial arson incident in the Washington region -- 37 fires have been set, along with one attempt -- and the third such attack in Northern Virginia, Blackwell said. Authorities blocked off streets surrounding the home and canvassed the area, talking to neighbors.

"Just like other crimes and like with the 8-year-old girl killed in the District, a tip from the community, regardless of how small people think it is, could help solve this whole series of arsons," said Capt. Chauncey Bowers of the Prince George's fire department, who serves as the arson task force spokesman.

Perez said he is glad the fire occurred on a weekday.

"If it was Saturday or Sunday, nobody gets up early and nobody would have seen the fire," he said.