As the tenants scrambled from their smoke-filled building into the morning rain Wednesday, the firemen who had been called to the desolate brick building in the Washington Highlands neighborhood in the far southeast corner of the city quickly doused the small basement fire.

A slender youth still inside the apartment building raised the window blind in his first-floor apartment and intently watched the scene. Women carrying babies and pet dogs clustered on the wet sidewalk outside. Firemen hurried into the building with heavy fans to clear the smoke.

"That's him right up there," said a tenant, gesturing at the figure in the window.

The youth stepped back and quickly lowered the blind.

The tenant, who is also the resident manager of the four-story apartment building, was referring to the person believed by many other tenants to have set the building on fire six or seven times in the last year. D.C. police believe he is responsible for about 30 other fires in the immediate neighborhood.

Later that afternoon police arerested the 17-year-old youth and charged him with the arson of his own apartment building.

The resident manager stood outside the apartment building, her red bedroom slippers and brown coat soaked by the rain. "We're terrified to live here," she said. "And we have to live with that person. He just likes fires."

As the tenants waited to return to their building, the firemen rolled up the hoses and loaded the truck. They glanced back at the building, looking for the face now familiar to them from photographs shown them by arson investigators.

"Did you see him?" asked one firefighter.

"No, I didn't see him in the hall. He must have stayed inside," another answered.

In a waiting game that started last year, firemen, police investigators and residents alike said they had a pretty good idea who the arsonist was. They all thought it was the same person. They knew his name. They had seen his picture many times, and they knew where he lived. But he was never arrested.

"We often know who an arsonist is but the difficulty is in proving it," said Battalion Chief Bernard Johnson, head of public information for the D.C. Fire Department. "You have to actually catch the person lighting the fire or have two collaborating witnesses who will testify they saw you light the fire . . . there must have been witneses" to justify an arrest.

The firefighters of Engine 25 and Truck 8 say they have fought most of the 30 fires set in the area since last August. Their 78-year-old firehouse at Fourth Street and Martin Luther King Jr. Avenue SE, which once looked out over farmers' fields, is now in the heart of acres of apartment complexes that cover the rolling hills.

The members of the fire company call the local arsonist "The Torch."

The Torch has impressed the firefighters not only with his ability to set so many successful fires but with the relatively large size of the fires.

"It's the magnitude of the fires that makes this guy different," said firefighter Ken Cox. "Your usual arsonist sets trash fires. This guy sets off whole top floors.

And he does it in his own, recognizable way, according to Capt. Joseph Lucas.

"He always starts them [on the top floor] in the kitchen with paper in the cabinets," Lucas said. "Then he punches holes in the ceiling and that allows the fire to really spread."

Firefighter John Morris is also impressed with the arsonist. "This guy is really a pro," he said. "He sets it to go and it takes the whole roof. He knows that type of fire will bring out a lot of trucks." Most of the fires have been set in vacant building. Fire officials gave no estimate on the damage to the approximately 20 buildings, several of which were set on fire more than once.

Another fireman suggested there may be two arsonists working in the area since the latest fire, for which the youth had been arrested, was a basement fire rather than the expected top-floor fire.

Seventeen-year fire department veteran Bob Ager scoffed at the idea.

"It's the same guy all right. He just doesn't do ceilings in his own place," he said.