Police experts here disagree whether a man who claimed to be the Hillside Stangler in a letter to Los Angeles Mayor Tom Bradley is the actual killer of 12 young women, a prankster or a memtally ill person with no connection to the crimes.

Assistant Police Chief Daryl Gates made public portions of a letter written by a person who said he was the killer.The letter writer said he was "very sick" and blamed his mother, whom he said he also had murdered.

"My mother told me to kill those bad and evil ladys," the letter said, in an evident reference to police identification of seven of the victims as prostitutes.

Police psychiatrists and psychologists who examined the hand-printed letter, which contained numerous misspellings, disagreed on its authenticity. But Gates said, "There are things in the letter that give it an air of urgency."

These things apparently include a threat by the strangler to strike again if there is no response to his letter. Gates said the writer gave a deadline that is now "within a week or two."

Gates said that another matter which "piqued the interest of myself and some very experienced investigators" was the mention of a certain item, which police have declined to identify. If the writer actually possesses the item, Gates said, it would demonstrate that he has knowledge of the crimes.

The last killings attributed to the Hillside Strangler occurred Dec. 14, when the nude body of Kimbely Diane Martin, 17, was found sprawled on a hillside in the Silver Lake area near Glendale. The other 11 murders occurred in the same area beginning Sept. 9.

Many of the victims lived or worked in an area of Hollywood and Glendale known for its rampant vice. Most prostitutes in this area have fled to other cities, either out of fear of the strangler or of the police crackdown on prostitution that the killings have produced.

Other than driving the prostitutes to cover, the 93-member Los Angeles police strangler task department's Hillside force has little to show for more than two months of intensive investigation.

This may be one of the reasons that the police have shown so much interest in the letter, somewhat to the surprise of Bradley, who left it lying unopened in his office after the returned from a Washington trip. The letter, dated Jan. 19, ultimately was opened Feb. 1 and turned over to police.