DENVER — Whether bought from a downtown shop or cadged from a friend's basement greenhouse, legal marijuana is easy to find in Colorado. Places to smoke it, not so much.

Smoking in private homes and on front porches is allowed. But under a thicket of state, local and private regulations, marijuana use here, in a state at the forefront of legalization, is banned from parks and sidewalks, airport smoking areas, hotel rooms, gallery events, nightclubs and nearly every other corner of public life. Smoking in public is regularly ticketed, and this spring, the Denver police raided two private, marijuana-friendly clubs and handed out citations.

But in the latest battle over legalizing marijuana, advocates are seeking to allow legal pot use to tiptoe ever so slightly into public, into establishments like bars or clubs that cater to over-21 crowds. Supporters are calling it "limited social cannabis use."