A D.C. Superior Court judge yesterday suppressed all evidence against cabdriver Charles Edward Allen III, who unwittingly chauffeured accused police killer Bruce Wazon Griffith to his death in a shootout with police last February and then was charged with illegal possession of a handgun and marijuana found in his cab after the incident.

Judge Shellie F. Bowers ruled police officers acted improperly by questioning Allen for several hours without formally arresting him and advising him of his right to remain silent.

Bowers' ruling, which came just before jury selection in the trial and reversed a position the judge had taken on Tuesday, blocked prosecutors from introducing a seven-page statement and oral confession Allen had made that the gun and marijuana were his.

On Tuesday, Bowers had ruled that police had detained Allen only as a witness to the Griffith shootout, not as a suspect in a crime and had no reason to arrest him until after the statements were made.

Defense attorney W. Edward Thompson argued that by detaining Allen for several hours, the police had effectively arrested him. Thompson also contended that police had coerced Allen's statement by threatening to charge him with accessory after the fact in the murder of the policeman that Griffith was accused of killing.

Yesterday, Bowers said he had changed his mind after finding a 1979 court case Dunaway v. New York , in which a man had been detained for a long period of time and had given a supposedly voluntary confession in a murder case but was not arrested and charged untl after the man had signed the confession.

Assistant U.S. Attorney Jerry Goren said yesterday the government has 10 days to decide whether to appeal Bowers' ruling ot drop the case. He acknowledged that Bowers' action virtually destroyed the government's case. If convicted of the charges, Allen could receive two years in jail and be fined $2,400.

Allen, whose cab was destroyed in the Northeast Washington shootout and who was downgraded in his D.C. public school job for being away from work on the day of the incident, said yesterday that Bowers' ruling was the first good news he had had since the incident. Allen drives another cab part time now, but said he doesn't work as often because the Griffith incident has left him "extremely nervous."

Allen's trouble began with a rambling joy ride Reb. 14 when Allen, trying to earn a few extra dollars hacking on his lunch hour from a Northwest D.C. school where he worked as an equipment engineer at the time, picked up Griffith at North Dakota Avenue and Blair Road NW.

Griffith, object of one of the city's most massive manhunts, appeared to be high on drugs and was in no hurry to go anywhere. He said he wanted to find a cocaine dealer and asked Allen to drive him around.

"I don't know this is a killer," Allen said later."We just hit it off right away." Allen said he saw an easy fare before he had to head back to work.

For the next 45 minutes, Allen's cab weaved in and out and around the side streets of Northeast D.C. near North Capitol Street and Seaton Place. They never did find the "cocaine man," Allen recounted.

With a radio blasting out a hit from the O'Jays, and Griffith trying to roll a joint in the front seat, the two men didn't notice a small brown car that had pulled in behind them. Two off-duty policemen in casual clothes were searching on their own time for Griffith and had spotted him in Allen's cab.

Moments later, a marked police car pulled alongside Allen and ordered him to pull over. Griffith told him to drive. Allen, not realizing what was happening, threw the car into park and jumped out as Griffith and the police exchanged a barrage of shots.