The trial of Gregory Benson, charged with the murder last year of Frank Flook on Capitol Hill, ended when D.C. Superior Court judge declared a mistrial yesterday afternoon after the jury in the case said it was unable to reach a verdict.

"Are you hopelessly deadlocked?" Chief Judge H. Carl Moultrie I asked the jury foreman.

"I believe we are," the foreman replied. "I do not believe any further deliberation will do any good."

Benson, 27, of 1523 A St. NE, had denied in testimony that he had been involved in the slaying last December of Flook, his next-door neighbor.

Marilyn Flook, the victim's wife, had identified Benson as one of two men who stood outside her front door just before her husband was slain on Dec. 27. w

However, Benson said he was watching television and talking on the phone in his home at about the time of the fatal shooting at 1521 A St.

"I haven't any business being down here," Benson said yesterday after the jury said it was unable to decide the case, "I'm not that stupid to go out and shoot my next-door neighbor."

Marilyn Flook, who had testified emotionally for three hours last week, said that "I'll continue as long as it takes, but it's not going to bring my husband back, which is what I really want."

Benson's lawyer said a juror had told him the vote was 9-3 "not guilty." It was indicated in the courtroom that the earliest a new trial could be held would be next January.

The Flooks were the only white couple living in the block of row houses in their neighborhood. The shooting outraged friends and neighbors, black and white. Benson, a member of one of the most popular families on the street, was arrested last March.

However, a D.C. Superior Court judge dismissed a first-degree murder charge against him, asserting that police lacked sufficient evidence to arrest him.

Benson was later indicted in May on a felony murder charge.