Prosecutors rested their case against Wayne B. Williams today after their last witness testified the accused killer had told her he would confess if police gathered enough evidence against him.

" 'Wayne, if they get enough evidence on you, will you confess?' " Sharon Blakely, a one-time business associate, said she asked Williams after police stopped him for questioning near the Chattahoochee River May 22. "And Wayne Williams said, 'Yes.' "

Two days later, the body of Nathaniel Cater, 27, washed up downstream near the spot where the body of Jimmy Ray Payne, 21, was found a month earlier. Williams is charged with those murders and prosecutors have introduced evidence from 10 other killings to show a "pattern or bent of mind."

Blakely, a jeweler with a sideline music-promotion business, said she asked Williams to explain why he had been on the bridge at the height of the slayings of 28 young blacks that terrorized this city for two years. " 'Don't worry about it,' " she said Williams told her. " 'I'm going to sue the news media and get rich.' I said, 'Wayne, before you get hurt, will you confess? The game has got to stop somewhere.' "

Under cross-examination, she said that "Wayne had a split personality. I'm not saying he's a psycho. Wayne needs help. Before the evidence got to be too much, he said he'd come forward and confess."

"Do you think Wayne Williams killed somebody?" asked Assistant Fulton County District Attorney Jack Mallard. She stared directly at the defendant.

"Yes, I do," she said. "I really feel Wayne Williams killed somebody and I'm sorry."

Blakely was the final prosecution witness in a murder case built on a mountain of circumstantial evidence, including fibers linking the pudgy, 23-year-old freelance TV cameraman and self-styled talent scout to 11 slain blacks and eyewitness accounts placing him with six victims. Williams has denied knowing any of them. There is no murder weapon. Coroners' reports attribute most of the deaths to strangulation or asphyxiation.

Prosecutors suggested a motive today as witnesses portrayed Williams as a black man who hated poor black children and wanted to purify his race by eliminating them. Bobby Toland, an ambulance driver who knew Williams as a news photographer of grisly accidents, said he "seemed ashamed of and angry at lower class blacks. He asked me if I knew 'how many niggers could be eliminated by doing away with one nigger child.' " Williams then quoted him statistics, he said.

Williams even had a derogatory nickname for the street kids he despised: "street grunchins." Two black street teen-agers have testified Williams offered them money for sex, and he was spotted holding hands with Cater the day before Cater disappeared.

Defense attorneys have depicted Williams as being too small and weak to throw anyone off a bridge. But Toland, a six-foot, 292-pound man, said Williams held his own in wrestling matches with him at the ambulance office. "He was a pretty strong fella," he said. Williams once sprayed Mace at him when they were horsing around and threatened to use chloroform or karate on anyone who picked on him, he said.

Witnesses also said he had severe scratches on his arms last year. Coroners have detailed autopsies of at least two youths on the list of 28 victims who put up a fight with their killer. Several were strangled, and a medical examiner testified earlier in the six-week-old trial that any strangler would likely have marks on the hands and arms.

Kathy Andrews, owner of a music studio Williams used to audition and record prospective talent, said that at one time "He had severe scratches from his elbow to his wrist, crosswise and down." She said Williams told her he "fell down." Another witness who had noticed the scratches said Williams told him his German shepherd, Sheba, bit him.

One youth he recruited said Williams warned him not to get killed on a trip out of town. Dennis Bentley, 14, said he wasn't worried. Then, he testified, Williams told him, "The last person who said that, I went to their funeral."

After Williams became a suspect, Bentley went for a ride with him, he testified. Police were on his tail. When the radio broadcast news about the killings, Williams switched the channel, Bentley said. According to Bentley, Williams kept looking in the rear-view mirror at police and said, "They ain't going to catch me. I wrote the book."

After the prosecution rested, defense attorney Alvin Binder asked Judge Clarence Cooper to dismiss the charges because the cases were based on "innuendo and circumstantial evidence. There are no eyewitnesses to murder ," only two bodies whose cause of death is asphyxiation. Cooper denied the motion.