Alphonso (Monk) Harris, one of two persons acquitted of murder charges three months ago in the brutal slaying of Catherine Fuller, was in fair condition late yesterday after being shot by an assailant when he answered a knock at his front door, D.C. police said.

According to a preliminary police investigation, Harris, 23, was shot in the left shoulder about 10:30 a.m. when he answered the door of his apartment at 815 Maryland Ave. NE., where he lives with his brother Anthony.

Harris, who was admitted to the Washington Hospital Center's Medstar unit, was questioned throughout the afternoon by detectives, some of whom worked on the Fuller case.

Police said they had no motive and no suspect in the shooting. Lt. William White III, the police department spokesman, said, "For me to speculate on the connection of the shooting to the Fuller trial at this time would be inappropriate."

Harris was one of 10 young persons charged with the 1984 slaying of Fuller, a 48-year-old Northeast woman who was accosted while shopping, dragged into an alley and pummeled to death while a crowd watched.

Harris was identified as having participated in the murder by two men who later pleaded guilty to lesser charges and testified for the prosecution.

No other witnesses placed him at the scene. Harris testified that he did not know many of the other defendants and was elsewhere when Fuller was killed. He and a 17-year-old girl were found not guilty.

The shooting caused a small reunion of principals from the trial who came to visit Harris. Corinne Schultz, one of Harris' lawyers, comforted Harris' mother Helen Brooks.

Detective Donald Gossage, whom Harris once shot in the leg with a BB gun and who worked persistently on the year-long investigation of the case, strolled in. Assistant U.S. Attorney Jerry S. Goren, the prosecutor in the case, arrived in a car driven by Detective Patrick McGinnis, another homicide detective in the case.

"I just came to see if he is okay, if he is going to live," Goren said.

Harris' mother, Helen Brooks, who was at the hospital, said: "I've been afraid of something like this , but I wasn't living every day thinking someone was going to shoot him. He thought he was safe.

"If it's a situation where it's a retaliation . . . we can't resolve anything by exchanging altercations. I don't know what this is about."

She said that her son, who was living with her on 14th Place NE at the time of the trial, moved in with his brother after the trial ended in December and was "still working on cars."

Harris was rushed to the critical care unit of the Washington Hospital Center because it was thought at first that his wound was more serious than it was.