Late last year, prosecutors in King County, which encompasses Seattle, became the first in the nation to stop charging people for possessing small amounts of drugs — heroin, meth and crack included — in virtually all cases. Many people who once would have been locked up are now immediately offered help through Law Enforcement Assisted Diversion (LEAD). It is a profound shift that builds on efforts launched here in recent years to divert low-level drug offenders into treatment and other programs to assist with recovery. The approach, which is being considered elsewhere, amounts to a bold experiment during a historic drug epidemic: Can a major American city beat drug abuse by treating it as a public health crisis rather than a crime?