Amid grim news of record deficits unveiled in the US budget, marijuana advocates are welcoming legislation in US states they say could blossom into billions of dollars in tax revenue.

San Francisco state lawmaker Tom Ammiano introduced a Bill last Monday projecting a 14-billion-dollar tax base for the full retail treatment - buying, selling and growing cannabis.

The leading legalisation advocacy group behind Mr Ammiano's Bill, Washington-based National Organisation for the Reform of Marijuana Laws (NORML), says recession is prompting otherwise sceptical state houses to revisit the ban on marijuana.

Over the last few months NORML has been drafted to work with state lawmakers - even in conservative locales like Texas - on budgetary analysis and review how legalisation may enable governments fill yawning deficits.

"Cannabis for adult recreation, cannabis for medical use, cannabis as an industrial crop, and (the drug's) related paraphernalia are extremely popular and should be taxed and properly regulated," NORML executive director Allen St Pierre told AFP. "It's just that simple."

Mr Ammiano's Bill used the most conservative estimates from NORML's analysis, he added.

On the west coast, no other cash crop comes close.

At the current consumption rate, California would likely "produce a tax base of up to 20 billion dollars per annum," according to Mr St Pierre.

Dispensaries in California - retail outlets throughout the state where medical marijuana patients buy weed - can take up to 50,000 dollars a day, he said. "This should make your eyes pop wide open if you're a financial commissioner."

But legalisation opponent Eric Voth is worried "the number of people who will start using or worsen their habit because of the lack of legal constraints is going to cost the system far more than what might be generated through taxation."

Mr Voth, chairman of the Institute on Global Drug Policy, contends marijuana advocates are "happy to lie to the public" about the gains of their proposals, with an end goal of cannabis legalisation "at any cost."

Long-time law enforcement lobbyist John Lovell, who represents the California Police Chiefs' Associations and the California Narcotic Officers Association, also raises questions. Mr Ammiano's Bill won't put the illicit marijuana market out of business, won't raise much money and will prompt an exponential growth in usage, he said.

"The last thing we need is yet another lawful product that impairs our ability to use our five senses," he contended, adding: "It makes no public policy sense."

Some 115 million Americans already live in the 13 states where marijuana is decriminalised to some degree.