LOS ANGELES (AP) _ A convicted murderer told police he has slain as many as 13 people nationwide and that one of his victims was a Los Angeles woman whose death was among 17 assigned to a serial murder task force.

Daniel Lee Siebert, 32, who faces the death penalty for the murder of a woman Talladega, Ala., is awaiting trial in Alabama in the slayings of two other women and two children.

He is also believed by authorities to be the killer of another Los Angeles woman, a Nevada woman, and a New York woman whose body was found in Atlantic City, N.J., Sheriff Sherman Block said Friday.

An itinerant commercial painter who frequented the Hollywood area in late 1985, Siebert is believed to be the killer of Los Angeles area residents Gidget Castro, 28, and Nesia Gail McElrath, 23, Block said.

The South Side Serial Murder Task Force is investigating the deaths of 17 women, mostly black prostitutes, who were killed between 1983 and July 1986. Most of the bodies were found in or near south-central Los Angeles.

Detectives believe the slayings are a series of murders by several people rather than a serial killing by one person. More than $2.6 million has been spent and more than 4,000 clues researched in the investigation so far.

Siebert has admitted as many as 13 killings across the United States, Block said, but he is not a suspect in any of the 16 other slayings under investigation by the task force.

''He didn't admit to any others, and he wouldn't have any reason not to admit to them,'' Block said. ''We did not believe that all the murders on the task force list were committed by a single person.''

Four of the women believed to have been killed by Siebert in Alabama were black. None was a prostitutes, Block said.

All the slayings now attributed to Siebert were strangulations.

Block said Siebert revealed his participation in the Los Angeles killings to Los Angeles sheriff's investigators who traveled to Alabama in recent days.

''He did admit to both murders. He revealed information known only to the person involved,'' Block said.

Sheriff's investigators are still in Alabama questioning Siebert and are not expected to return until Monday, he said.

Ms. McElrath's body was discovered Dec. 19, 1985, in a rural area near Castaic, in northern Los Angeles County. Because of the distant location of her body, she was not listed officially as one of the South Side victims.

The body of Ms. Castro was found in an alley in the City of Commerce, which is south of Los Angeles, on Dec. 26, 1985.

Alabama authorities alerted Los Angeles investigators to Siebert's potential as a suspect, Block said.

Even though Siebert faces the death penalty for his Alabama murder conviction, Block said Los Angeles authorities eventually will attempt to get him returned to California.

''I'm certain there will be an effort to extradite him,'' Block said.