A British man was killed and a dozen persons were hospitalized early yesterday after a poorly ventilated furnace in a Takoma Park rooming house filled the building with poisonous carbon monoxide fumes, fire investigators said.

Takoma Park fire officials said 41-year-old Lewis Horton of London, who slept in a room directly above the furnace room, was found dead by fire and rescue workers about 6:30 a.m. in his bedroom at 13 Lee Ave.

Seven other residents of the house and five firefighters were hospitalized; four of the residents and two of the officers were transferred to the shock-trauma unit at University of Maryland Hospital in Baltimore for a special blood procedure that is used to restore the proper oxygen level.

Takoma Park Fire Chief Roger McGary said the investigation is continuing. He said that the house had been cited several times for housing code violations, but had been brought into compliance.

McGary said that rescue workers were called to the house shortly after 4 a.m., when one of the residents, James Henry Clark, complained of chest pains. Clark was "waiting at the curbside" for the ambulance, McGary said, so none of the rescue workers went inside at that time. He was treated at nearby Washington Adventist Hospital and released.

Two hours later, when they received a report of "several sick people" at the same address, McGary said, another ambulance and a fire truck crew responded. Using gas masks, they removed the seven residents and Horton's body, then called a Washington Gas Light crew to the scene.

McGary said the carbon monoxide was the result of "incomplete combustion" within the furnace. A preliminary investigation, he said, had revealed three factors that probably contributed to the problem. Pieces of the terra cotta chimney liner had fallen into the air stack; the adjustable ports that are intended to provide the proper air-gas balance were closed, and the furnace room and the adjoining room had only one window each, which were tightly sealed with plastic.

McGary said the occupants had been complaining of nausea and headaches for several days, "but they all thought they had the flu, just passing it around the house."