Wayne B. Williams was convicted tonight of two murders in a string of 28 slayings of young blacks that terrorized this southern city for 22 months.

Williams, a self-styled music promoter, was sentenced immediately to two consecutive life terms. Under Georgia law, he can apply for parole review in seven years.

Judge Clarence Cooper asked Williams if he had anything to tell the court. A stoical Williams, standing between his attorneys and his father, said:

"I have maintained my innocence all through this trial, and I will still say so today. I just hope the person or persons who committed these crimes can be brought to justice. That comes from the bottom of my heart.

"I, more than anyone, wanted to see this terror ended, but I did not do it," he declared in a soft, earnest voice.

A jury of eight blacks and four whites deliberated for 12 hours over a two-day period before finding Williams guilty of murdering Nathaniel Cater, 27, a day laborer with a drinking problem, and Jimmy Ray Payne, 21, a convicted burglar who yearned to be a singer.

After the sentencing, Williams was led away in handcuffs. Mary Welcome, one of his attorneys, wept quietly. His father, Homer Williams, bit his lip and scowled.

The jury filed into the wood-paneled courtroom packed with 18 armed deputies and reporters at 7:07 p.m. Cooper asked the prosecutor to read the verdict.

Fulton County District Attorney Lewis Slaton walked to the jury box and took the verdict sheet from the foreman, Sandra Laney. "We the jury find the defendant, Wayne Bertram Williams, guilty on count No. 1," he said. "We the jury find the defendant . . . guilty on count No. 2."

Williams' father, a retired school teacher, said of the verdict: "I feel there is an error in justice.

"I don't see how anybody, anywhere, could find my son guilty of anything. Anyone who sat in this courtroom for the last nine weeks could see that no one has brought any evidence to show my son guilty of anything," he said. "It's very unfair."

The case will be appealed, said defense lawyer Alvin Binder of Jackson, Miss. He pinned the conviction on fiber evidence plucked from the victims that experts testified matched materials from Williams' home and car.

"It was the fibers," he said. "It sure wasn't the witnesses."

There were no witnesses to the murders. But the prosecution provided a mountain of circumstantial evidence.

Fiber experts for the prosecution connected Williams to Cater, Payne and 10 other victims the prosecution was allowed to introduce through more than 700 microscopic fibers and dog hairs.

The fibers taken from the bodies by medical examiners matched fibers from Williams' green bedroom carpet, a blue bath mat, 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, 1981, FBI search of his home.

Dog hairs were also found on the victims that matched hair from his German shepherd, Sheba.

In addition, prosecution witnesses testified that there were two bloodstains in the back seat of a station wagon that matched blood types on two victims.

Witnesses placed Williams with seven victims, including Cater and Payne. And one day laborer testified that he saw Williams holding hands with Cater downtown in May, 1981.

Slaton heralded the verdict as a victory for scientific fiber analysis, predicting that it would raise the forensic art to a science.

"When I had him locked up, I didn't expect any more of these killings and we didn't see any more," the prosecutor said. Since Williams became a suspect last May, there have been no similar killings of young black men. Slaton reminded the jury of that Friday, when he called Williams cool and cunning and compared him to Adolf Hitler.

At 4:30 p.m., the jury sent Cooper a note saying it had reached a verdict on one count. He ordered them to continue deliberating. They asked to extend their work day until 8 p.m., then sent word that they were ready.

The death penalty was ruled out in the case because the crimes did not fit special circumstances under Georgia law.

The Atlanta killings unfolded as a murder mystery that began on a hot day in July, 1979, when a woman scavenging for aluminum cans off Nisky Lake Road discovered the body of Edward Hope Smith, 14. He had been shot in the head. In the kudzu nearby was Alfred James Evans, 13. He had been strangled.

Evans was among the 10 victims prosecutors were allowed to introduce in the trial to show a pattern in the murders with which Williams was charged.

But no investigation was launched until one year later, after the toll of black children had climbed to five dead and three missing.

Police were skeptical at first, finding no statistical significance in the deaths of young ghetto blacks, and officials were accused of insensitivity toward the urban poor. In July, 1980, a year after the first two bodies were found, a small Atlanta police task force began studying the deaths in a basement cubbyhole at police headquarters.

Soon, the special task force on missing and murdered children ballooned to 125 federal, state and local police, and President Reagan made $1.5 million in federal funds available for the investigation.

In the meantime, the killings were taking a toll on the city, turning its southside ghettos into frightened, armed camps. Children carried knives and guns to school and fearful mothers kept them close to home. Children had nightmares of the "snatcher," as the elusive killer came to be called, and some were shipped away to live with relatives outside the city.

The City Council instituted a dawn-to-dusk curfew for children under 14 to keep them off the street. The victims got older.

Police hunted for a pattern but about all there was to connect the victims, most of them boys, was their impoverished backgrounds: they were poor and black and hustled for spending money doing odd jobs.

Authorities were baffled. Then came a turning point in the investigation: bodies began turning up in rivers after The Atlanta Constitution published an article that said police had discovered fibers on the bodies that connected several victims. The killer, investigators theorized, had started trying to wash his victims clean of incriminating evidence.

Police staked out bridges at night, trying to catch a killer. Then came the break, authorities thought.

Recruits on stakeout duty beneath a bridge at the Chattahoochee River heard a loud splash. It was about 2:50 a.m., May 22, when police stopped Wayne Williams for questioning after he crept across the Jackson Parkway Bridge in the family's white station wagon.

Two days later he became a suspect when Cater's nude body was plucked from the river downstream, near where Payne's body had been found a month earlier.