The state Office of Financial Management produced an estimate this week on the fiscal impact of the potential passage of Initiative 502, which will be on the November ballot.
However, the analysis notes that revenues would be "adversely impacted" if federal authorities cracked down on the state, as they threatened to do when California voters were considering legalizing the drug in 2010. Marijuana is illegal under federal law.
I-502 would create a system of state-licensed growers, processors and stores, and impose a 25 percent excise tax at each stage. People ages 21 and older could buy up to an ounce of dried marijuana, one pound of marijuana-infused product in solid form, such as brownies, or 72 ounces of marijuana-infused liquids.
The analysis anticipates 100 state-licensed growers supplying more than 300 marijuana stores that would sell 187,666 pounds to at least 363,000 customers. Those numbers are based on federal drug-use surveys.
The state also includes a second scenario, with 10 percent higher consumption, in which the total tax revenue would be $606 million. The tax revenue could reach near two-thirds of a billion dollars by fiscal year 2017, according to the report.
The state estimates are significantly higher than the $215 million that I-502's campaign estimated would be raised from the excise taxes.
"The campaign has always wanted to be conservative in the estimates on the revenue because we honestly don't know what a legal marijuana market will look like," said campaign director Alison Holcomb.
Even though the analysis was prepared by Gov. Chris Gregoire's budget staff, the governor is opposed to the initiative.
"This doesn't resolve the conflict with federal law," said her spokeswoman, Karina Shagren.
In addition to Gregoire, a group of medical-marijuana patients oppose I-502, saying the initiative's proposed driving-under-the-influence provisions would make it impossible for many patients to legally drive. That group, No on 502, had raised no money as of late February. I-502 has raised $1.2 million since last May but spent much of it on paid signature gathering to qualify for the ballot, according to public disclosure reports.