An FBI agent, testifying today at the trial of Wayne Williams, said investigators were unable to verify Williams' account of his activities last May 22, the night he was stopped by a police stakeout near a Chattahoochee River bridge.

Williams, a self-styled talent scout on trial here for the slayings of two young black Atlantans, told the FBI investigator he was searching for the address of Cheryl Johnson, a young woman who had asked for an audition. He couldn't find it, he told police, and he tried to telephone Johnson.

But when FBI agents dialed Johnson's telephone number--the same number Williams said he tried--they reached Merle Norman Cosmetics, an FBI agent testified today.

Special agent William McGrath, an 11-year veteran coordinating some 40 agents investigating the murders of 28 young blacks here, asked Williams in an interview at his home "what he was doing on the Jackson Parkway bridge" above the Chattahoochee River moments before police heard a loud splash.

Two days later, the naked body of Nathaniel Cater, 27, was found snagged on a tree downstream, near the spot where the body of Jimmy Ray Payne had washed up a month earlier. Williams is accused of killing Cater and Payne and dumping their bodies in the river.

In an interview at Williams' home, McGrath said, Williams said he was trying to locate Johnson's apartment so he would know how to find it later that morning when he planned to discuss auditioning her for a TV commercial. McGrath said Williams told him he dialed her number and someone came on the line, telling him, "She ain't here."

A telephone company security investigator testified that no such number was in service at the time. When McGrath dialed it, he said he first got a recording saying the number had been changed. The new number reached the cosmetics firm. On cross-examination by defense attorney Alvin Binder, McGrath acknowledged Williams told him he might have gotten the last digit wrong.

Agents also said Williams told them he thought Johnson lived at the Spanish Trace apartments, but the apartment manager testified she had no record of any resident by that name. Williams also gave police an address for Johnson's apartment, but the manager of the only complex on that road testified she had no record of the woman.

Williams also told police he saw a small blue pickup truck or van he believed to be a Purolator courier on the bridge, but the courier service manager testified that all his trucks were across town at the time. Under cross-examination, the manager conceded that there are several courier services with blue-and-white trucks. Police have testified that no other vehicles were on the bridge when Williams drove across.

McGrath said he didn't arrest Williams after his interview because "there were other avenues to be explored. This was a sensitive investigation. We certainly didn't want to be premature in arresting somebody without fully checking out his story."

McGrath said Williams told him he had stopped Thursday night, hours before the bridge incident early Friday morning, to try to retrieve a tape recorder he had loaned to San Souci nightclub manager Wilbur Jordan, a partner in the talent business. But Bolton said Williams came by for the tape recorder the next evening. Under cross-examination, Binder tried to show that Williams could have tried to fetch his recorder Thursday night without anyone remembering him.

Williams also told police he played basketball on a Schlitz beer team, but a Schlitz official testified that there was no official company team. Binder suggested that a team could play basketball in "Schlitz" jerseys, however.