But the bill is hobbling through the House, where it was stripped this month of the parts that would allow legalization. As of Friday, it contains only a cautious provision to allow home-growing and legalized possession of small amounts of marijuana — well short of the regulated market that Mr. Shumlin has called for.

Lawmakers’ largest concerns are those that have emerged in state after state as the legalization movement has taken off: use and abuse by young people, impaired driving and commercialization.

But the opiate crisis, in which heroin, fentanyl and other drugs have killed more than 2,000 people in New England in the last year, is a substantial stumbling block, complicating efforts throughout the region and figuring into anti-legalization political alliances.

“At a time when we are trying and working so desperately hard to get help to those who need it, telling young people to not do drugs, trying to eliminate some of the barriers to treatment and to promote recovery, this effort at legalization seems to be directly at odds with those efforts,” said Maura Healey, the attorney general in Massachusetts and a Democrat, who opposes an initiative that is expected to land on the ballot in November. It would allow adults to possess up to 10 ounces of marijuana at home, permit edibles and create a regulated market.

Advocates are using the heroin crisis as an argument in favor of legalization, saying that it would move the substance out of the hands of traffickers and that it “would reduce the amount of interaction with hard drug dealers, period,” said Matt Simon, the New England political director of the Marijuana Policy Project, a national organization working on legalization.