LOS ANGELES, Aug. 28 – More than two months of a costly trial went for naught Friday when a mistrial was declared in the murder proceedings against Steve Grogan, a member of the Charles Manson “family.”

Superior Judge Joseph L. Call issued the order after a day of soul-searching, sometimes in heated debate with prosecution and defense attorneys.

At 3:23 p.m., after 14 jurors, including two alternates, had been locked up four hours in the windowless room adjoining the court chamber, the jurist announced his decision.

Grogan, 20, is accused of the decapitation murder of cowboy actor Donald J. (Shorty) Shea, 35, in the last days of August, 1969.

The prosecution contends that the Manson group killed him because he had married a black woman: they suspected him of being a police informer, and they thought he had been hired to evict them from the Spahn movie ranch in Chatsworth.

The turning point came Thursday while Dep. Dist. Atty. Burton S. Katz was cross-examining the third defense witness, Nancy Pitman, 20, a family member also known as Brenda McCann.

Katz asked her if she and Grogan had ever discussed killing Frank Retz, who owned an adjoining ranch and later bought the Spahn place. She denied there had ever been such a discussion.

But defense attorney Charles V. Weedman moved for mistrial, contending that the idea that Grogan might be guilty of another crime — with which he has not been charged — had been implanted in the minds of the jurors and they could no longer return a fair verdict.

Jurors, seven women and five men, and the alternates, a man and a woman, were excused for the day but Katz and Weedman were summoned into chambers. Katz bitterly opposed ordering a mistrial.

“I am highly disturbed about this,” the judge told them in reference to the mention of Retz. “I am seriously considering granting the mistrial motion.”

When the time came for the ruling the jurist said he believed the mention of Retz had been so “prejudicial and inflammatory” that the defendant could not have an impartial trial.

Grogan will be taken before Superior Judge Richard F. C. Hayden next Thursday for setting of a new trial date.

Ironically, none of the jurors gave much importance to the Retz remark. All agreed, in discussions after their discharge, that they had expected Miss Pitman to say nothing derogatory about Grogan.

“It was obvious to me that she intended her testimony to be as favorable as possible to the defense,” said alternate juror John Sweden Jr. “So the question and answer about Mr. Retz made no particular impression on me.”

Most of the jurors conceded that they had been impressed by the prosecution’s 37 witnesses, even though Shea’s body has never been found. But they said they would have retained an open mind about their verdict until they had heard all defense testimony.

Two jurors, however, expressed the belief that a guilty verdict would have been returned. John A. Brooks so indicated, and Carlos C. Sequeida said he was “leaning toward guilty.”

The trial cost the taxpayers $2,052 a day, based on the latest survey made under direction of Frank S. Zolin, the Superior Court’s executive officer. The trial began June 23.

Call’s ruling was made while the trials of Manson and another family member, Charles (Tex) Watson, were in recess. Manson is accused of the Shea murder and that of musician Gary Hinman.

Watson is being tried for the seven Tate-LaBianca killings for which Manson and three girl followers are already under sentence of death.

By RUDY VILLASENOR