Testimony ended today in the nine-week murder trial of Wayne B. Williams with his mother's plea to the jury that "Wayne's character has been drug through the mud."

"They continue to lie and lie," said Faye Williams, a retired teacher, "but they have not produced any evidence that my son is a killer."

That is the question the jury of eight black and four white persons could begin pondering as soon as Friday afternoon. Closing arguments are scheduled to begin at 9 a.m. in a roller-coaster murder trial that has produced a mountain of circumstantial evidence against Williams but no "smoking gun."

Jurors will be asked to weigh crucial scientific fiber evidence tying Williams to the victims and police accounts of his behavior against the credibility of the defendant, his parents and defense experts.

No one has testified that he saw Williams kill Nathaniel Cater, 27, or Jimmy Ray Payne, 21, the two young black men Williams has been charged with killing, or any of the other 10 victims about which prosecuters have been allowed to introduce material to show a "pattern, scheme or bent of mind" in the cases.

Yet prosecutors have brought in an army of damaging witnesses in an attempt to paint him as a homosexual "Jekyll and Hyde" who hated poor black youngsters, sexually propositioned them, then murdered them because he wanted to purify his race.

Testimony has suggested that their inability to hustle their way out of the ghetto mirrored his failure as a self-styled music promoter.

Perhaps most damaging to his case was Williams' performance on the stand Wednesday, when at one point he called Jack Mallard, the assistant Fulton County district attorney, a "fool."

In other comments he displayed a volcanic temper and a contempt for police.

It was dramatic counterpoint to his stony demeanor on the stand the previous two days, and his portrayal by the defense as a polite, all-American altar boy and grade-school electronics whiz with, at worst, poor grades in college and a penchant for hype.

Before Mallard was finished, Williams had called FBI agents who questioned him "goons" and police who contradicted his account of events the night Cater disappeared "liars." By the time he sat down he was crying.

Rebuttal testimony today capped an attempt by prosecutors to cement a connection between Williams and the victims through more than 700 microscopic fibers and dog hairs taken from their bodies. Fiber experts from the FBI and the Georgia Crime Laboratory testified earlier that it would have been virtually impossible for Williams and the victims not to have come into contact.

Fibers from the victims, they said, matched fibers from Williams' green bedroom carpet, a blue bathmat, green carpet squares in a workroom, carpeting in his car, glove lining, threads from his bedspread and a yellow blanket that disappeared after a June 3 FBI search of his home.

Moreover, two bloodstains in the back seat of his station wagon matched blood types on two victims, prosecution witnesses testified.

Witnesses placed him with seven victims, including Cater and Payne. And one laborer testified that he saw Williams holding hands with Cater downtown on May 21, 1981, six hours before police say Williams dumped Cater's body in the river.

The murders of Cater and Payne were among a series of 28 killings of young blacks, mostly young men, that terrorized this city during a 22-month period beginning in July, 1979. There have been no similar deaths since Williams' arrest last June 23. Williams was first questioned by police about 2:50 a.m. May 22, shortly after officers on stakeout at the Jackson Parkway Bridge over the Chattahoochee River heard a splash in the water.

Police stopped Williams' car as he was driving across the bridge. Two days later Cater's nude body washed up downstream, near the spot where Payne was pulled from the river a month earlier.

Williams told officers that he was out hunting the address of an aspiring singer, Sheryl Johnson, who has never been located. But Mallard shot holes in the contradictory accounts of that evening's events Williams gave to police and the FBI and at a news conference June 4.

Prosecutors also produced witnesses who said Williams had muscles, boasted about karate and carried Mace, contradicting defense claims that the defendant was a pudgy weakling unable to hoist a body over a bridge railing.

Prosecutors have portrayed him as a police buff who bragged that he knew karate, ridiculed the FBI as "Keystone Kops" and displayed a violent temper. A parking lot attendant today said he had seen Williams attack Williams' father after the elder Williams refused to rent a car for his son's friend.

A member of Williams' singing group, Gemini, said Wednesday that he had watched Homer Williams threaten his son with a shotgun after Wayne beat and choked him for refusing to write a check for Wayne's music venture.

The defense has tried to portray Williams as the victim of a huge conspiracy to find a killer at all costs.

Defense experts pitched fiber analysis as more art than science, and attacked autopsy reports as insufficient to prove the deaths were homocides. Judge Clarence Cooper today denied a second defense motion for a directed verdict of acquittalbased on that claim