Investigators are making progress toward solving the murders of 20 black children in Atlanta and are checking "lines of coincidence" between those crimes and the New York state arrest of a former convict charged with kidnapping a 9-year-old black child, FBI Director William Webster said yesterday.

Webster said a lot of work remains to be done. "Sometimes we take one step forward and two steps backward," he remarked of the long effort to catch the killers of 20 black children in Atlanta.

Some new information has been unearthed as a result of improvement of laboratory work in Atlanta following the arrival there of the assistant director of the FBI's Laboratory Division, Webster said.

He declined to tell reporters the nature of the new information during brief remarks on the Atlanta case. He said that the improved forensic work resulted from better coordination among all the investigating agencies and better technical capabilities.

The director unequivocally agreed with other investigators who have said that more than one murderer is responsible for the 20 deaths in Altanta. Two children remain missing there as well.

He also was strongly critical of the vigilante groups that have moved into Atlanta. "It's too much of an invitation to violence from groups to come in and take the law into their own hands," Webster said. He added that he is in favor of the "watch groups" that simply undertake to protect citizens by keeping streets and parks under observation. "I'm not in favor of the ones with bats," he said of the vigilantes.

Asked about the arrest in East Fishkill, N.Y., of Frankie Albert Edmonds, who is accused of kidnapping a child and holding him in the back of a rented van, Webster indicated that the possibility of a connection to the Atlanta murders was being taken very seriously.

"I can't tell you whether he [Edmonds] has been named by us as a suspect," Webster said. "It's too early to tell the significance of the New York arrest."

The circumstances of the arrest of Edmonds, 32, were peculiar.

Edmonds, according to police, had at first reportedly abducted the child near a school playground in the town of Beacon, N.Y.

He then allegedly drove 20 miles to the neighboring town of East Fishkill, where he left the child in the van, and drew attention to himself going from door to door, claiming he was looking for his girlfriend. Townspeople, considering his behavior "suspicious," alerted the police. Edmonds, who is black, at first told police the boy was his brother, but during an interview at the stationhouse the child "calmed down and opened up" and said he had been abducted, according to Fishkill police. Edmonds was charged with unlawful imprisonment and endangering the welfare of a minor and held in Dutchess County Jail in lieu of $25,000 bail.

The alleged abduction, the fact that Edmonds had been driving a vehicle with Georgia plates, and the fact that he had also been found with a flyer promoting a march in honor of the slain Atlanta children prompted police to contact the FBI, who began questioning the suspect yesterday.

Spokesman at the FBI's local headquarters in New Rochelle refused any comment on the case. They declined to say whether Edmonds was considered a serious suspect in the Atlanta killings, or even if he had been in Atlanta at the time. (Spokesman for the Ryder Co., from which the van had been leased, did say that the fact that the van had Georgia plates was insignificant -- it might have been rented anywhere.)

But the arrests touched off a blaze of speculation. Neighbors of Edmonds in the New York City borough of Queens spent the day telling reporters that Edmonds had been a "weird and scary" guy who had been away from the home he shared with his family for at least three months. Edmonds' father, Hilbert Edmonds, however, insisted to reporters that his son "hasn't been in Georgia in his life."

"He was found with a kid, but he didn't abduct him," Hilbert Edmonds told the New York Post, adding his son "has mental problems" and "was in jail for a while." The man's distraught mother, reportedly weeping, said her son "is a stupid fool at times," but he ain't no Atlanta killer."

New York State Correctional Services spokesman, meanwhile, confirmed that Edmonds had served time in prison between 1976 and 1978 for weapons possession and in 1968 for the same charge.