SEATTLE — Surrounded by thousands of packages of marijuana, Seattle’s top prosecutor sought some advice: Which one should he buy?

A new day, indeed.

Twenty months after voters legalized recreational cannabis for adults over 21, Washington state’s first few licensed pot shops opened for business Tuesday, catering to hundreds of customers who lined up outside, thrilled to be part of the historic moment.

The pot being sold at four stores in Seattle, Bellingham, Prosser and Spokane was regulated, tested for impurities, heavily taxed and in short supply — such short supply that several other shops couldn’t open because they had nothing to sell.

Pete Holmes, Seattle’s elected city attorney and a main backer of the state’s recreational marijuana law, said he wanted to be one of the first customers to demonstrate there are alternatives to the nation’s failed drug war.