Nine residents of a Northwest Washington group home for mental patients were killed and at least six others were injured when flames swept through the three-story building early today.

The fire in a three-story duplex building at 1715-17 Lamont St. NW. in the Mount Pleasant neighborhood, caused the worst loss of life in recent city history.

John Johnson, who lives in an apartment building next door at 1713 Lamont St., said he was awakened shortly after 1 a.m. and looked out the window to see "every windor of the building in flames . . . it looked like one gigantic fireplace."

He and his wife, Ophelia, said they saw two elderlly women jump from a second-floor window at 1715 Lamont. Mrs. Johnson said one woman landed on her knees "really hysterical." The other woman was lying dead a few feet away, she said.

The facility housed outpatients from St. Elizabeths Hospital, the federally owned mental hospital in Southeast Washington, and was operated by the Volunteers of America, a community oriented service group.

Bodies of many of the dead, all elderly, were found scattered in various rooms throughout the building.

Denise Hilton, resident manager of the facility, said the fire started in a couch located in a special second floor smoking room for residents in the rear of the structure.

She said she was told by a resident that the couch had been set afire by a cigarette. Hilton said she attempted to extinguish the blaze but it got out of control and spread quickly through out the building.

The flames trapped most of the building's 22 residents inside, and more than a dozen attempted to jump to safety from upper stories, fire officials said.

The injured were taken to Washington Hospital Center, where the nursing supervisor said five women between the ages of 40 and 60 were treated for minor burns, smoke inhalation and cuts and bruises. Their conditions were listed as satisfactory to fair. Other injured were reported stillen route to the hospital.

Fire equipment converging on the scene was hampered by the narrow streets in a neighborhood composed of largely row houses built around the turn of the century.

Deputy D.C. Police Chief Houston M. Bigelow said the Volunteers had operated the home since last February. Prior to that, the residence had been operated by others for about 12 years, Bigelow said. He said the Volunteers manage another, similar home in the District.

Of those who died, according to fire officials, three were found on the third floor, five on the second and the body of one who jumped was found in the yard. No identities were available.

Four men living in the basement of the structure were reported to have escaped without injury.

In terms of death toll, the fire was the worst in recent history in the city since nine men died in a fire that swept the Cinema Follies, a Southeast Washington film club for homosexuals, on Oct. 24, 1977.