Authorities have more evidence against Wayne B. Williams than they presented in court Tuesday in the murder of the most recent of 28 young blacks slain here, police superintendent Lee Brown said today.

"There was not a full-blown presentation of all the evidence available," he said. "That will come out in trial."

Despite Brown's assurances, many Atlantans openly question whether police have the right man. They wonder why police waited three weeks to areest Williams, a pudgy free-lance TV cameraman-turned-record promoter, after first questioning him, and they want reassurances that the officers do have more solid evidence than officials have revealed so far.

The only evidence made public so far linking Williams and Nathaniel Cater, a day laborer whose body was taken from a river here last month, are two fibers found in the victim's hair that matched those taken from Williams' bedroom, three or four dog hairs taken from Carter that appear "microscopically consistent" with hair from Williams' dog, and a splash one policeman heard in the river as Williams' car was spotted driving across the river two days before the body was discovered.

"No one even saw his car stop on the bridge that night," his defense attorney, Mary Welcome, told a courthouse news conference Tuesday as her client was led back to his isolation cell in handcuffs.

She scoffed at the fiber evidence as "very, very weak." The only was Williams could have thrown a body off the bridge, she said, was as his car was moving, which she called a virtual impossibility: the body weighed as much as he did.

"Any one of you, under the circumstances, could have killed Carter," she said. "You all have fibers in your hair. My client is innocent, he did not kill anyone. No one even saw his car stop on the bridge that night."

As for the splash heard by the officer, who sources say was asleep in his pup tent at the time, she speculated that it could have been made by a beaver. An officer assigned to the bridge stakeout the night Williams was spotted conceded under cross-examination that one of his men had complained about beavers.

Questions are raised not only about the quality of the evidence by why authorities waited so long to arrest Williams.

Local newspaper accounts suggest that political pressure was applied from as far away as Vice President Bush's office to make an arrest, a version denied by a spokesman for Bush. Other sources say Williams' father had inquired about renting a plane, which police feared Williams might use to flee the city. Then there was the suspect's erratic, high-speed driving, which twice in recent weeks had shaken police tailing him for brief periods.

As recently as last week, the Fulton County district attorney, Lewis Slaton, denigrated the evidence he would have to relay on, evidence some sources say didn't change before the arrest Sunday.

Slayton declined to say in an interview today what changed his mind, but conceded that he would like to have more evidence.

"I don't have any cases where I wouldn't like to have more evidence," said Slaton, a respected prosecutor with a high conviction rate who is known for his cautious approach to cases.

He hinted that he had something more up his sleeve. "I put up just enough for the hearing, no more," he said.

"At a preliminary hearing, you put up as little as possible, just enough to get by," said a high-ranking source close to the investigation. "You don't want to give anything away. As long as he's in custody and in jail, it gives us more time to go about investigating him methodically."

After three hours of testimony by police officers and a microanalyst Tuesday, a state judge ordered Williams brought before a grand jury to face possible indictment for the murder of Cater.

Prosecutors are not 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.

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