Tom Potter, the former police chief who served as Portland's mayor from 2004-08, so far has been quietly supporting Measure 74, the ballot initiative that aims to create a regulated system of medicinal marijuana dispensaries in Oregon.

Without much fuss, his name is appended to an argument in favor of the measure. It's among a list of arguments that supporters have paid hundreds of dollars to include in a state-produced guidebook mailed to voters.

Campaign sources, however, say that's about to change. Potter is scheduled tomorrow to record a radio advertisement in favor of the measure, part of a broader crunch-time effort by the campaign that also will include a public statement of support from the American Civil Liberties Union.

The ad is still being refined, but I'm told Potter is expected to tout his law-and-order credentials, play up his avuncular nature, and explain that the measure's attempts at regulation (which we suggest should be stronger) have helped sway him from his previous stance against medicinal marijuana.

I've got a message to see whether Potter or anyone who can speak for him has anything more to say.