SEATTLE -- More than 150,000 denizens of the Northwest will gather this weekend in a waterfront park for Hempfest, billed as the largest promarijuana gathering in the country, to listen to speeches from the biggest names in the national drug-law reform movement between band sets and bong hits. But this year, attendees will hear an explicitly partisan message, too: Organizers are pushing pot smokers to help elect Senator John F. Kerry president. The size of Hempfest indicates the potential power of the pro-pot vote, particularly in the Northwest, reformers said.