It was Halloween night when Ron Lawler opened his door and saw flames shooting up though the floor of his porch. The next night, his neighbor, Patrick Lanius, came home from work to find his partially renovated house had also been set on fire.

Neither resident of the neighborhood around Marion and Q streets NW in the heart of Shaw knows who started the fires or why. The police detective assigned to the case calls it a mystery.

This tiny downtown neighborhood on the urban frontier is typical of the changing Shaw area. The two-story brick row houses with bay fronts and tiny yards are occupied mostly by longtime residents who have rented their houses for years, along with a few new homeowners who moved in during the past five years. There are drug trafficking problems in the area and complaints during the summer of noisy children playing ball in the street.

What is not typical of this or other downtown neighborhoods is the two deliberately set fires.

Lawler said the fire at his house, which he extinguished with trashcans full of water before the fire department arrived, has left him anxious and worried but determined to stay in the house he bought 2 1/2 years ago.

Lanius, 28, said when he got home, the fire was already out, the fire department was gone and his neighbors had boarded up the broken window.

"I did two things," said Lanius, who has lived in his house for the past year while renovating it.

"I bought smoke detectors and fire extinguishers, and I took the 'For Sale' sign out of the window," he said. "My parents and girlfriend talked me into selling the house this summer. Now I am staying."

Lanius, Lawler and other residents of the neighborhood guess that the fires, which caused only minor damage, were set in retaliation for a concerted effort over the past several years to move the cocaine, heroin and PCP dealers off their block.

Lawler, 41, said that he didn't realize he had bought a house in a drug-trafficking neighborhood until he moved to Q Street from Alexandria.

"When we first moved in, we had to move 15 people off our steps every night when we came home from work," he said.

"They were selling 'lovely' PCP . We called the police two or three times a day, and mostly they came. Finally they did a roadblock this year and that reduced the drug traffic down to just the neighborhood dealers."

There has also been friction between Lawler and neighborhood youths who, like city youngsters everywhere, use the intersection as a playground.

Det. Norman Boone, who is investigating both arsons, said he doubted that the fires were set by drug dealers. "If the drug dealers were intent on burning down those houses, they would have done it better," he said. "And it doesn't look like what kids would do. They may throw a rock through a window, but they wouldn't firebomb a place. The who and the why, we just don't know. It is a mystery at this point."

Ibrahim Mumin, head of the Shaw Project rea Committee and a neighbor of Lawler's, said that when he and his family were actively involved in driving the drug traffic from Q Street last year, they were theatened with arson, too.

"A year ago we had trouble with one drug dealer right here on our block," said Mumin. "They theatened to firebomb our house. That is the raw reality when you fight to clean up drugs. You are interfering with people making money. We were blessed and nothing happened to us."

The mix of black and white, gay and straight, old and young seems to work pretty well at Marion and Q streets. Wilbur Mackall, 62, who has lived on Marion Street for 30 years, said the newer residents are good neighbors. "There is a white couple that lives around the corner on Q Street. When I was sick, they were real nice to me," he said. "The block is pretty quiet now. There used to be drugs around here, but they the newcomers helped improve it."

Maxine Welsh, who lives directly across the street from Lanius, said proudly that her son was the one who called the fire department when he saw the fire in Lanius' basement window.

Nine-year-old Lawrence Welsh recalled that he and a friend were playing in a parking lot behind the old Shaw Junior High School, now a senior citizens' residence.

"I saw the white light in the basement," he said. "The flames were coming out the window. I saw someone run down the alley the other way and I ran home to tell my father. He told me to call the fire department. I did just what my teacher said to do. I called 911 and said, 'Please connect me to the fire department' . . . .I was kind of nervous. It was the second fire I ever saw but the first time I called the fire department."

Wednesday night, Lanius, Lawler and 12 other neighbors gathered at the home of a neighbor, Russ Blumer, to meet with police officials.

The officials suggested that they meet with the police regularly, leave City Council member John A. Wilson (D-Ward 2) out of the picture and form a neighborhood watch group. Blumer, 28, dismissed the advice.

"We formed a neighborhood watch program a month ago. I am the block captain," he said. "We have already petitioned Wilson to help us close up a house where drug dealers congregate. They are just offering us an eyewash, trying to soothe us.

"We need to uninvolve ourselves from the city," he went on. "We are going to have to do this ourselves. We are going to apply economic pressure and buy that house ourselves.

"Whoever started those fires did nothing but help us. We have been coming together slowly for the past two years. Now we have come together so fast and so tight that we have bonded. They have only made us stronger."