The Florida man who confessed last week to abducting and decapitating 6-year-old Adam Walsh, the subject of a recent television drama, is one of a pair of homicidal drifters who may turn out to be the worst mass murderers of modern times, according to law enforcement officials.

Ottis Elwood Toole, 36, now serving a 20-to-25-year term in Jacksonville, Fla., for arson, and Henry Lee Lucas, 47, who is jailed in Denton, Tex., awaiting a murder trial Nov. 7, have astounded authorities over the past four months with detailed accounts of the random and exceptionally grisly murders they claim to have committed all over the country.

Lucas alone says he has killed 165 people, most of them hitchhikers, stranded motorists or drifters like him. Toole has told authorities he participated in up to 50 of those murders in 1976-1982, when the two men traveled from coast to coast as homosexual lovers. He has also confessed to setting more than 50 fires.

Lucas began making the confessions after he was picked up in rural Montague County, Tex., in June on a weapons charge. His written accounts eventually prompted 85 law enforcement officers from 25 states to meet two weeks ago in Monroe, La., to exchange notes on his trail of crime.

The authorities concluded that they already have enough evidence to charge one or both men with 28 murders in eight states. They also say they may be able to develop charges against the pair for another 69 unsolved murders in a total of 13 states.

"We were able to eliminate some of the crimes as not having been possible for them to commit, but I'd still say they may have commited the biggest string of murders in history," said Sgt. Jay Via, of the Ouachita Parish sheriff's office in Louisiana, who helped to put the conference together.

Sgt. Via speculated that the two had managed to escape arrest for so long because "they traveled constantly and they had no clear m.o. [modus operandi]. They stabbed their victims, bludgeoned them, shot them. You name it, they did it."

Some of the killings were associated with robberies, but the vast majority were sexually motivated, Via said.

"Both men were necrophiliacs. They had sex with their victims after killing them, sometimes they had sex with their victims before killing them," Via said. Toole is homosexual, Lucas bisexual.

Lucas has told officers that he first killed when he was 13; his victim was a woman who spurned his sexual advances. He was first convicted of murder in 1960 for killing his 74-year-old mother, Viola. He spent six years at a state hospital for the criminally insane in Michigan, was returned to prison and paroled in 1970.

He was convicted in 1971 for the attempted kidnaping of a young girl, served his sentence and was released in 1975.

In 1976 he met Toole in a relief mission in Jacksonville, Fla., and the two spent the next six years traveling from coast to coast, living off crime and odd jobs. They split up in 1982, authorities said, with Toole returning to Florida and Lucas drifting from Texas to California.

His travels ended in June when he was picked up for questioning, and eventually charged with the murder of an 80-year-old Montague County, Tex., woman with whom he had lived as a boarder for a brief time.

Last month he pleaded guilty in that case and was sentenced to 75 years in prison. Lucas faces another murder trial Nov. 7 in Denton, Tex., and his court-appointed attorney, Thomas Whitlock, has already notified the court he will offer an insanity defense.

In that case, Lucas is charged with the 1982 slaying of his 15-year-old common-law wife, Frieda (Becky) Powell, who was Toole's niece.

According to a videotaped confession that has been ruled admissible as evidence, the killing was committed as the two were hitchhiking through Texas and arguing about whether to return to Florida. Lucas said he stabbed Powell, dismembered her body with a 10-inch kitchen knife and stuffed it into a pillowcase.

"I hope you find all of her," Lucas said in the confession. "I didn't do it because I didn't love her. It was because of the argument and the difficulty I have had in my life."