Fibers taken from the body of a day laborer pulled from a river here last month show "no significant microscopic difference" from fibers found in the bedroom of Wayne B. Williams, the freelance TV cameraman and music promoter under arrest for murdering the black man.

After three hours of such testimony in a courtroom jammed with reporters and curious people off Peachtree Street, a state judge ordered Williams brought before a grand jury to face possible indictment for the murder of Nathaniel Cater, 27. Cater is the latest victim in the string of 28 murders of young blacks here.

Fulton County District Attorney Lewis Slaton said he will present his case against Williams within 30 days.

Williams was arrested Sunday and charged with the murder of Cater, whose nude body was pulled from the muddy Chattahoochee River May 24, two days after police staking out a bridge over the river heard a loud splash and spotted Williams driving across the bridge.

Cater had been strangled, like 17 other victims who have died from various forms of asphyxiation. He was the sixth to be pulled from the Chattahoochee. f

Prosecutors aren't charging Williams with any other killings, but Slaton has said he believes the Cater murder is probably linked to the 13 most recent slayings of young blacks that have baffled authorities for the last two years.

The testimony on the fibers, the first official glimpse at the state's case against Williams, came from a state crime lab microanalyst who compared several fibers from Cater's body with those retrieved from Williams' bedroom in the modest red brick home he shares with his parents, both retired teachers. i

The lab technician, Larry Peterson, said he found "no significant microscopic differences," between a violet fiber from Williams' bedspread and one he took from Cater's head with a pair of tweezers May 24. Among about a dozen fibers he found on the body, one closely matched the green carpet in the bedroom, he said.

He also said three or four dog hairs found on Cater also were "consistent microscopically" with hairs taken from Williams' German shepherd.

"Is there anything else that connects Mr. Williams with the death of Mr. Cater?" asked an assistant defense attorney, Tony Axam.

"Not at this time," Peterson said.

Axam then characterized the case against his client as based on "speculation and surmise of the type seen in a newspaper," and asked the judge to dismiss it. The motion was denied.

Also called to testify was Freddie Jacobs, an Atlanta police rookie who was part of Chattahoochee River stakeout team early May 22 when Williams was stopped by police after traveling over the bridge. Jacobs testified that at about 3 a.m. another rookie cop below the bridge said over the radio, "Freddie, is there anyone up on the bridge? I just heard a loud splash down here."

Jacbos radioed back immediately, "Yes, I see a car up here." The car drove slowly "like it was coming from a parked position," he testified. It cruised across the bridge, turned around in a liquor store parking lot, then "shot back over the bridge," he said.

Moments later, police pulled Williams' white station wagon over near an interstate ramp and saw two large bags of clothing in the car, along with a pair of dirty gloves and a flashlight, Jacobs testified. He identified the driver as Williams. Two days later Cater's body was found several hundred yards from the bridge, near the spot where another victim, Jimmy Ray Payne, 13, had been found earlier.

Williams was immediately put under surveillance, but soon discovered that police planes and cars were following him. When officials realized that Williams had spotted the surveillance they invited him on June 3 to local FBI headquarters for questioning. Twelve hours later he was released, and Public Safety Commissioner Lee Brown said there was insufficient evidence to make an arrest.

For the last 2 1/2 weeks there has been mounting political and law enforcement pressure on Slaton to try Williams for Cater's murder. And it was disclosed today that Gov. George Busbee and Atlant Mayor Maynard Jackson agreed last week that if he did not act to prosecute Williams they would consider appointing a special prosecutor.

Slaton refused to say whether he had any more evidence than before, when he hesitated to bring Williams to trial based on circumstantial evidence that largely revolves around the fibers and the bridge incident.

But he did say in a courthouse interview today that he was moved to favor arresting Williams after Williams began leading police on highspeed drives past the house of the mayor and the public safety commissioner.

He also said there was speculation about Williams' leaving town. Slayton said that in recent days investigators had "talked to more people" in the Williams case, but he declined to say how strongly those interviews bolstered his case.

Some of today's evidence was gathered during a search of Williams' home June 3, but authorities returned Monday afternoon for a more comprehensive search that lasted 10 1/2 hours.

At least seven large paper bags of material and a large piece of green carpeting were carried off in two vans. Officers searched a crawl space underneath the house, and scavenged through garbage cans and searched the yard. uOne officer said technicians inside were lifting fingerprints in an attempt to match them with any of the victims' fingerprints they have on file.

Fiber evidence is largely circumstantial by nature, experts say. No test can prove that one fiber is identical to another, just that the fibers could be the same.