SEATTLE  Washington State law prohibits the possession of marijuana except for certain medical purposes. Hempfest is not one of them. Yet each summer when the event draws thousands to the Seattle waterfront to call for decriminalizing marijuana, participants light up in clear view of police officers. And they rarely get arrested.

“Police officers patrolling are courteous and respectful,” said Alison Holcomb, drug policy director for the American Civil Liberties Union of Washington.

One reason for the officers’ approach, said Ms. Holcomb and others who follow law enforcement in Seattle, is the leadership of R. Gil Kerlikowske, the chief of the Seattle Police Department and, officials in the Obama administration say, the president’s choice to become the head of the Office of National Drug Control Policy, known as the drug czar.

The anticipated selection of Chief Kerlikowske has given hope to those who want national drug policy to shift from an emphasis on arrest and prosecution to methods more like those employed in Seattle: intervention, treatment and a reduction of problems drug use can cause, a tactic known as harm reduction. Chief Kerlikowske is not necessarily regarded as having forcefully led those efforts, but he has not gotten in the way of them.