LOS ANGELES, Aug. 13 — The drug-dominated culture of the Charles Manson family was vividly described in court here Thursday by a witness who said he decided to quit the group when he realized that he would be expected to do some killing.

Paul A. Watkins, 21, his shoulder-length hair parted in the middle, gave his views as a prosecution witness under cross-examination at the trial of Steve “Clem” Grogan, 20, for the decapitation-murder of cowboy actor Donald J. “Shorty” Shea, in August, 1969.

The witness said that when the 20-odd members of the group took LSD Manson insisted that they all remain in one room because anyone leaving could be picked up by police and thus bring trouble to the rest.

Nevertheless, Watkins testified, on some occasions individuals managed to escape while under the drug’s influence, including one girl who “ran into the hills” carrying a knife and razor blades and threatening to kill herself. Manson himself, the witness recalled, once violated his own rules by leaving while, under the influence of LSD and was missing for a day and a half.

Watkins said that when he first joined the family in March, 1968, Manson preached that revolution would begin when oppressed blacks would kill families in rich white neighborhoods. The whites would then retaliate, Watkins quoted Manson as saying, and eventually all whites would be killed.

But Manson had a remedy for his group, Watkins continued, by providing that they would all be safe “in a hole in the desert” from which they would emerge 144,000 strong in 50 years. By then, Watkins said, Manson predicted that the blacks would be remorseful and would accept the role of servants to the whites.

“He said that he would pat the blacks on their fuzzy heads, kick their butts and tell them to go pick the cotton,” Watkins told the jury in Los Angeles Superior Court Judge Joseph L. Call’s court.

But Manson eventually decided that he would not wait for the revolution to start but would begin it himself, meanwhile kidnaping while babies to be raised by the family in the desert.

“I went for it wholeheartedly,” Watkins said. “We were all to wake up one morning and find nothing but peace on earth.”

But the witness recalled that when he found that he would be expected to do some of the killing himself, he “turned off.”

Watkins also remembered that even after he no longer lived with the family he paid visits at the Spahn movie ranch in Chatsworth, Calif., and various other places the nomadic family occupied.

Watkins said he returned to what remained of the family even after Manson and others had been arrested for the Tate-LaBianca murders. During part of this time, Watkins said he shared living quarters with Grogan.