LOS ANGELES, Aug. 29 — The murder trial of Manson cultist Steve Grogan came to an abrupt end on Friday when the judge declared a mistrial because of a single prejudicial question posed by the prosecution.

Grogan 20, charged with participating in the slaying of movie stuntman Donald (Shorty) Shea in 1969, now faces the prospect of a new trial. Meantime, he will remain in jail without bond.

Trial Judge Joseph L. Call made his ruling to grant a defense mistrial motion following a daylong closed-door conference with attorneys.

The abrupt end — after six weeks of trial — surprised even some of the jurors. After they were dismissed, many told newsmen they couldn’t even recall the prejudicial question which led to the defense motion.

Judge Call, however, ruled that the question — which prosecutor Burton Katz posed to a defense witness on Thursday — was “so inflammatory” that it would prevent a fair and impartial trial for Grogan.

The decision came just one day after the proceedings were interrupted because of a reported death threat to defense attorney Charles Weedman. There was no official indication that the two developments were related.

Katz’s question hinted that Grogan may have planned to commit another murder.

Following Judge Call’s ruling, the case was sent back to the master calendar court where presumably a new trial will be scheduled. A hearing was set for Sept. 2 in Superior Court Dept. 100.

The prosecution contends that Grogan — along with clan leader Charles Manson and another follower, Bruce Davis — killed Shea in August 1969, although no body has been found.

Manson and Davis are being tried separately.

Shea 35, worked at the Spahn Ranch in Chatsworth which, at the time, was headquarters for the Manson “family.”

The question which caused the mistrial was posed by Katz late Thursday to defense witness Nancy Pitman 20, a longtime family member.

“Isn’t it true that you and Clem K (the name by which Grogan was known in the “family”) were talking about getting a gun to kill Frank Retz?” Katz asked.

Retz was the owner of an adjacent ranch.

At that point, Weedman jumped to his feet and objected and the judge called both Weedman and Katz into chambers.

They met behind closed doors briefly and then resumed the discussion Friday morning.

The flare-up over the question came after less than a day of defense testimony.

The prosecution rested Aug. 19, but the trial was recessed until Wednesday when Weedman began presenting his evidence.

The proceedings were delayed several hours Thursday morning when Judge Call summoned attorneys into his chambers to consider the telephone death threat against Weedman.

The defense attorney reported receiving the threat from an anonymous man who complained the attorney wasn’t “doing enough” for Grogan.

Miss Pitman was called to the stand in an effort to rebut testimony from the prosecution’s star witness

— Paul Watkins 21, a former “family” member.

Watkins said Grogan admitted to him that he had chopped off Shea’s head. He said that Miss Pittman, also known as Brenda McCann, was present during the conversation.

During direct examination by Weedman, Miss Pittman said she never heard Grogan say any such thing. She insisted that the conversation in September 1969 dealt only with Watkins’ upcoming draft physical.

Trying to counter her testimony, Katz asked her about possible involvement with Grogan in another murder scheme.

Weedman said he objected to the question because it dealt with an issue that had not been raised before in the trial.

“It was outside the scope of the cross-examination and highly prejudicial to my client,” said Weedman, who was appointed by the court to defend Grogan.

“It was implanted in the minds of the jury and was impossible for the defense to counteract.”

Katz declined to comment on Judge Call’s decision.

Newsmen talked with several jurors as they filed from the courtroom after being discussed by the judge. Many said they couldn’t recall the prejudicial question or were prepared to disregard it anyway.

“No, I was not inflamed by the question,” said a woman juror who declined use of her name.

“I had not formed an opinion,” said a man juror.

“I totally disregarded Brenda’s (Miss Pitman) answers anyway because I knew she would say anything to help Grogan,” remarked a man who served as an alternate juror.

Most of the members of the jury of seven men and five women said they were disappointed at the mistrial decision and would have preferred completing the case.