POLICE Chief Daryl Gates has told two of his staunchest City Council allies that he wants a search for his successor to begin and that he will retire when one is named, the council members said Saturday.Chief Gates indicated he would outline his retirement plans in a letter to the City Council, council president John Ferraro said. "He did tell me he was looking into the possibility of writing a letter. How soon I don't know," Mr. Ferraro said in a telephone interview. "I believe that between his age, length of service, and simply the incredible pressure that he's under these days, it would seem that it's time to pull out," said Councilwoman Joy Picus, a strong supporter of the embattled chief. Gates had remained defiant under increasing pressure to step down in light of the Rodney King beating incident. Four of his officers face felony charges in the beating of the unarmed motorist that was captured on a nearby resident's videotape camera. The pressure had mounted with the release of the report by the Christopher Commission which cited an undercurrent of racism and brutality in the police department and recommended that reform begin with a transition to a new chief.